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Sample records for colloid stabilization mechanism

  1. Increasing entropy for colloidal stabilization

    Science.gov (United States)

    Mo, Songping; Shao, Xuefeng; Chen, Ying; Cheng, Zhengdong

    2016-11-01

    Stability is of paramount importance in colloidal applications. Attraction between colloidal particles is believed to lead to particle aggregation and phase separation; hence, stability improvement can be achieved through either increasing repulsion or reducing attraction by modifying the fluid medium or by using additives. Two traditional mechanisms for colloidal stability are electrostatic stabilization and steric stabilization. However, stability improvement by mixing attractive and unstable particles has rarely been considered. Here, we emphasize the function of mixing entropy in colloidal stabilization. Dispersion stability improvement is demonstrated by mixing suspensions of attractive nanosized titania spheres and platelets. A three-dimensional phase diagram is proposed to illustrate the collaborative effects of particle mixing and particle attraction on colloidal stability. This discovery provides a novel method for enhancing colloidal stability and opens a novel opportunity for engineering applications.

  2. Enhanced colloidal stability of hydroxyapatite

    Science.gov (United States)

    Borum, La Rhonda Terese

    stabilized the HAp particles in aqueous solutions via electrostatic interactions. Heterocoagulation was proposed as the predominant coating mechanism at this loading. The last technique investigated was the adsorption of the cationic polymer, polyethylene imine (PEI). PEI improved the colloidal stability of HAp in aqueous systems through electrosteric interactions.

  3. Mechanical Failure in Colloidal Gels

    Science.gov (United States)

    Kodger, Thomas Edward

    When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form

  4. Proteolytic stability in colloidal systems.

    NARCIS (Netherlands)

    Maste, M.C.L.

    1996-01-01

    Proteolytic enzymes in liquid detergents suffer from lack of stability in the sense that activity diminishes with time. Although the phenomenon could be attributed to several factors, the influence of colloidal surfaces on the enzymatic stability was investigated. Besides the types of surfaces that

  5. The prepatation and stability of homodisperse colloidal haematite (alpha-Fe2-O3)

    NARCIS (Netherlands)

    Penners, N.H.G.

    1985-01-01

    Since the foundation of colloid chemistry as a branch of science, much attention has been paid to the subject of colloid stability, i.e. the stability of colloid systems against aggregation. Gradually, our knowledge of the mechanisms involved has improved and models were developed, comprised in the

  6. Manipulating semiconductor colloidal stability through doping.

    Science.gov (United States)

    Fleharty, Mark E; van Swol, Frank; Petsev, Dimiter N

    2014-10-10

    The interface between a doped semiconductor material and electrolyte solution is of considerable fundamental interest, and is relevant to systems of practical importance. Both adjacent domains contain mobile charges, which respond to potential variations. This is exploited to design electronic and optoelectronic sensors, and other enabling semiconductor colloidal materials. We show that the charge mobility in both phases leads to a new type of interaction between semiconductor colloids suspended in aqueous electrolyte solutions. This interaction is due to the electrostatic response of the semiconductor interior to disturbances in the external field upon the approach of two particles. The electrostatic repulsion between two charged colloids is reduced from the one governed by the charged groups present at the particles surfaces. This type of interaction is unique to semiconductor particles and may have a substantial effect on the suspension dynamics and stability.

  7. Stabilization of Colloidal Silica Using Small Polyols

    Energy Technology Data Exchange (ETDEWEB)

    GULLEY, GERALD L.; MARTIN, JAMES E.

    1999-09-07

    We have discovered that small polyols are reasonably effective at stabilizing colloidal silica against aggregation, even under the conditions of high pH and salt concentration. Both quasielastic and elastic light scattering were used to show that these polyols dramatically decrease the aggregation rate of the suspension, changing the growth kinetics from diffusion-limited cluster-cluster aggregation to reaction-limited cluster-cluster aggregation. These polyols maybe useful in the treatment of tank wastes at the Hanford site.

  8. Sustainable steric stabilization of colloidal titania nanoparticles

    Science.gov (United States)

    Elbasuney, Sherif

    2017-07-01

    A route to produce a stable colloidal suspension is essential if mono-dispersed particles are to be successfully synthesized, isolated, and used in subsequent nanocomposite manufacture. Dispersing nanoparticles in fluids was found to be an important approach for avoiding poor dispersion characteristics. However, there is still a great tendency for colloidal nanoparticles to flocculate over time. Steric stabilization can prevent coagulation by introducing a thick adsorbed organic layer which constitutes a significant steric barrier that can prevent the particle surfaces from coming into direct contact. One of the main features of hydrothermal synthesis technique is that it offers novel approaches for sustainable nanoparticle surface modification. This manuscript reports on the sustainable steric stabilization of titanium dioxide nanoparticles. Nanoparticle surface modification was performed via two main approaches including post-synthesis and in situ surface modification. The tuneable hydrothermal conditions (i.e. temperature, pressure, flow rates, and surfactant addition) were optimized to enable controlled steric stabilization in a continuous fashion. Effective post synthesis surface modification with organic ligand (dodecenyl succinic anhydride (DDSA)) was achieved; the optimum surface coating temperature was reported to be 180-240 °C to ensure DDSA ring opening and binding to titania nanoparticles. Organic-modified titania demonstrated complete change in surface properties from hydrophilic to hydrophobic and exhibited phase transfer from the aqueous phase to the organic phase. Exclusive surface modification in the reactor was found to be an effective approach; it demonstrated surfactant loading level 2.2 times that of post synthesis surface modification. Titania was also stabilized in aqueous media using poly acrylic acid (PAA) as polar polymeric dispersant. PAA-titania nanoparticles demonstrated a durable amorphous polymeric layer of 2 nm thickness. This

  9. Bonding assembled colloids without loss of colloidal stability

    NARCIS (Netherlands)

    Vutukuri, H.R.; Stiefelhagen, J.C.P.; Vissers, T; Imhof, A.; van Blaaderen, A.

    2012-01-01

    In recent years the diversity of self-assembled colloidal structures has strongly increased, as it is fueled by a wide range of applications in materials science and also in soft condensed-matter physics.[1–4] Some potential applications include photonic bandgap (PBG) crystals, materials for plasmon

  10. Preparation of colloidal Sb2O5 and its stability

    Institute of Scientific and Technical Information of China (English)

    陈文汩; 张利; 龚竹青

    2004-01-01

    Colloidal antimony pentoxide was prepared by oxidation of antimony trioxide with hydrogen peroxide as oxidant and phosphoric acid as stabilizer. Effects of stabilizer, oxidant amount and reaction temperature on the diameter of colloidal particles and their size distribution were discussed. And static electricity effects on colloidal stability were studied by measurement of Zeta potential. Results show that Zeta potential of colloidal Sb2 O5 moves from -30mV to -56.8 mV with the addition of H3 PO4 as the stabilizer, zero point of charge of colloidal H3 PO4-Sb2 O5 moves from pH= 1.85 to more acidic regions, and colloidal H3 PO4-Sb2 O5 is stable in wider pH range. The stable time of colloidal H3 PO4-Sb2 O5 particles without coagulation is more than six months. The size of colloidal particles is smaller and their distribution is narrower by adding H3 PO4 as the stabilizer and decreasing reaction temperature, and the average diameter of H3 PO4-Sb2 O5 particles prepared is 30 nm.

  11. The Colloidal Stability of Magnetic Nanoparticles in Ionic Liquids

    Science.gov (United States)

    2015-08-03

    Final 3. DATES COVERED (From - To) 14 May 2014 – 13 May 2015 4. TITLE AND SUBTITLE The Colloidal Stability of Magnetic Nanoparticles in...Rev. 8-98) Prescribed by ANSI Std Z39-18 Final Report for AOARD Grant 144062 “The Colloidal Stability of Magnetic Nanoparticles in Ionic Liquids...sterically stabilized magnetic nanoparticles : Magnetic nanoparticles with an average core diameter of 25 nm used in this work were obtained from

  12. Sodium meta-autunite colloids: Synthesis, characterization,stability

    Energy Technology Data Exchange (ETDEWEB)

    zzuoping@lbl.gov

    2004-04-10

    Waste forms of U such as those in the United States Department of Energy's Hanford Site often contain high concentrations of Na and P. Low solubility sodium uranyl phosphates such as sodium meta-autunite have the potential to form mobile colloids that can facilitate transport of this radionuclide. In order to understand the geochemical behavior of uranyl phosphate colloids, we synthesized sodiummeta-autunite colloids, and characterized their morphology, chemical composition, structure, dehydration, and surface charge. The stability of these synthetic plate-shaped colloids was tested with respect to time and pH. The highest aggregation rate was observed at pH 3, and the rate decreases as pH increases, indicating that higher stability of colloid dispersion under neutral and alkaline pH conditions. The synthetic colloids are all negatively charged and no isoelectric points were found over a pH range of 3 to 9. The zeta-potentials of the colloids in the phosphate solution show a strong pH-dependence in the more acidic range over time, but are relatively constant in the neutral and alkaline pH range. The geochemical behavior of the synthetic colloids can be interpreted using DLVO theory. The results suggest that formation of mobile sodium meta-autunite colloids can enhance the transport of U in some contaminated sediments.

  13. Aqueous Colloidal Stability of Graphene Oxide and Chemically Converted Graphene

    Directory of Open Access Journals (Sweden)

    Swarnima Kashyap

    2014-01-01

    Full Text Available Graphene oxide (GO was prepared by modified Hummer’s method, and chemically converted graphene (CCG was prepared by further reduction of the aqueous GO colloid. The effect of pH on particle size, particle charge, and light absorption of the aqueous colloids of GO and CCG was studied with titration against HCl or NaOH, to find the ideal characteristics for a stable dispersion. The GO colloid was stable in the pH range of 4–11, whereas the CCG colloid gained stability at a relatively narrower pH range of 7–10. Poor stability of the colloids was observed for both GO and CCG colloids at both extremes of the pH scale. Both of the colloids exhibited average size of ~1 micron in the low pH range, whereas for higher pH the size ranged between 300 and 500 nm. The UV-Vis spectra showed absorption peak at 230 nm for GO colloids that shifted to 260 nm for the CCG colloid. Such shift can be ascribed to restoring of electronic conjugation of the C=C bonds in CCG.

  14. Colloid suspension stability and transport through unsaturated porous media

    Energy Technology Data Exchange (ETDEWEB)

    McGraw, M.A.; Kaplan, D.I.

    1997-04-01

    Contaminant transport is traditionally modeled in a two-phase system: a mobile aqueous phase and an immobile solid phase. Over the last 15 years, there has been an increasing awareness of a third, mobile solid phase. This mobile solid phase, or mobile colloids, are organic or inorganic submicron-sized particles that move with groundwater flow. When colloids are present, the net effect on radionuclide transport is that radionuclides can move faster through the system. It is not known whether mobile colloids exist in the subsurface environment of the Hanford Site. Furthermore, it is not known if mobile colloids would likely exist in a plume emanating from a Low Level Waste (LLW) disposal site. No attempt was made in this study to ascertain whether colloids would form. Instead, experiments and calculations were conducted to evaluate the likelihood that colloids, if formed, would remain in suspension and move through saturated and unsaturated sediments. The objectives of this study were to evaluate three aspects of colloid-facilitated transport of radionuclides as they specifically relate to the LLW Performance Assessment. These objectives were: (1) determine if the chemical conditions likely to exist in the near and far field of the proposed disposal site are prone to induce flocculation (settling of colloids from suspension) or dispersion of naturally occurring Hanford colloids, (2) identify the important mechanisms likely involved in the removal of colloids from a Hanford sediment, and (3) determine if colloids can move through unsaturated porous media.

  15. Maximizing exosome colloidal stability following electroporation.

    Science.gov (United States)

    Hood, Joshua L; Scott, Michael J; Wickline, Samuel A

    2014-03-01

    Development of exosome-based semisynthetic nanovesicles for diagnostic and therapeutic purposes requires novel approaches to load exosomes with cargo. Electroporation has previously been used to load exosomes with RNA. However, investigations into exosome colloidal stability following electroporation have not been considered. Herein, we report the development of a unique trehalose pulse media (TPM) that minimizes exosome aggregation following electroporation. Dynamic light scattering (DLS) and RNA absorbance were employed to determine the extent of exosome aggregation and electroextraction post electroporation in TPM compared to common PBS pulse media or sucrose pulse media (SPM). Use of TPM to disaggregate melanoma exosomes post electroporation was dependent on both exosome concentration and electric field strength. TPM maximized exosome dispersal post electroporation for both homogenous B16 melanoma and heterogeneous human serum-derived populations of exosomes. Moreover, TPM enabled heavy cargo loading of melanoma exosomes with 5nm superparamagnetic iron oxide nanoparticles (SPION5) while maintaining original exosome size and minimizing exosome aggregation as evidenced by transmission electron microscopy. Loading exosomes with SPION5 increased exosome density on sucrose gradients. This provides a simple, label-free means of enriching exogenously modified exosomes and introduces the potential for MRI-driven theranostic exosome investigations in vivo.

  16. Colloid aspects of chemical-mechanical planarization.

    Science.gov (United States)

    Matijević, E; Babu, S V

    2008-04-01

    The essential parts of interconnects for silicon based logic and memory devices consist of metal wiring (e.g. copper), a barrier metal (Ta, TaN), and of insulation (SiO2, low-k polymer). The deposition of the conducting metal cannot be confined to trenches, resulting in additional coverage of Cu and Ta/TaN on the surface of the dielectrics, yielding an electrically conducting continuous but an uneven surface. The surplus metal must be removed until a perfectly flat surface consisting of electrically isolated metal lines is achieved with no imperfections. This task is accomplished by the chemical-mechanical planarization (CMP) process, in which the wafer is polished with a slurry containing abrasives of finely dispersed particles in submicrometer to nanometer size. The slurries also contain dissolved chemicals to modify the surfaces to be planarized. Eventually the final product must be cleared of any adhered particles and debris left after polishing is completed. Obviously the entire process deals with materials and interactions which are the focal subjects of colloid and surface science, such as the natures of abrasive particles and their stability in the slurry, the properties of various surfaces and their modifications, adhesion and detachment of the particles and different methods for the characterization of constituents, as well as elucidation of the relevant interfacial phenomena. This review endeavors to describe the colloid approach to optimize the materials and processes in order to achieve desirable polish rates and final surfaces with no imperfections. Specifically, the effects of the composition, size, shape, and charge of abrasive particles on the polish process and the quality of planarized wafers is described in detail. Furthermore, the interactions of metal surfaces with oxidizing, chelating, and other species which affect the dissolution and surface modification of metal (copper) surfaces are illustrated and related to the planarization process

  17. Colloid Aspects of Chemical-Mechanical Planarization

    Directory of Open Access Journals (Sweden)

    Matijević, E.

    2010-09-01

    Full Text Available The essential parts of interconnects for silicon based logic and memory devices consist of metal wiring (e.g. copper, a barrier metal (Ta, TaN, and of insulation (SiO2 , low-k polymer. The deposition of the conducting metal cannot be confined to trenches, resulting in additional coverage of Cu and Ta/TaN on the surface of the dielectrics, yielding an electrically conducting continuous but an uneven surface. The surplus metal must be removed until a perfectly flat surface consisting of electrically isolated metal lines is achieved with no imperfections. This task is accomplished by the chemical-mechanical planarization (CMP process, in which the wafer is polished with a slurry containing abrasives of finely dispersed particles in submicrometer to nanometer size. The slurries also contain dissolved chemicals to modify the surfaces to be planarized. Eventually the final product must be cleared of any adhered particles and debris left after polishing is completed. Obviously the entire process deals with materials and interactions which are the focal subjects of colloid and surface science, such as the natures of abrasive particles and their stability in the slurry, the properties of various surfaces and their modifications, adhesion and detachment of the particles and different methods for the characterization of constituents, as well as elucidation of the relevant interfacial phenomena. This review endeavors to describe the colloid approach to optimize the materials and processes in order to achieve desirable polish rates and final surfaces with no imperfections. Specifically, the effects of the composition, size, shape, and charge of abrasive particles on the polish process and the quality of planarized wafers is described in detail. Furthermore, the interactions of metal surfaces with oxidizing, chelating, and other species which affect the dissolution and surface modification of metal (copper surfaces are illustrated and related to the

  18. Assessing colloidal stability of long term MWCNT based nanofluids.

    Science.gov (United States)

    Lamas, Bruno; Abreu, Bruno; Fonseca, Alexandra; Martins, Nelson; Oliveira, Mónica

    2012-09-01

    This report presents an assessment on colloidal stability of functionalized multiwalled carbon nanotubes based nanofluids. To this end, an innovative technique that allows for measurement of settling velocity during centrifugation is applied. This method also enables measurements without dilution, inferring further accuracy to the experimental study. The results suggest that functionalization techniques enable the production of highly stable nanofluids. It is also found, that the colloidal stabilities of these nanofluids are characterized by hindered settling. The settling velocity decreases when the nanoparticles volume fraction rises from 0.25% to 1.50% due to the increase of interparticle interaction. Furthermore, a high aspect ratio of nanoparticles directly contributed to an increase in colloidal stability. It is expected that these results may significantly contribute to proper tailor of nanofluids engineering, ensuring a long term stable dispersion enhancing industrial application suitability.

  19. Formation and stability of aluminosilicate colloids by coprecipitation

    Energy Technology Data Exchange (ETDEWEB)

    Putri, Kirana Yuniati

    2011-02-15

    Colloids are ubiquitous in natural waters. Colloid-facilitated migration is of importance in safety assessment of a nuclear waste disposal. Aluminosilicate colloids are considered to be the kernel of aquatic colloids. Their stability is affected by a number of geochemical parameters. This work aims to study qualitatively and quantitatively the stability of aluminosilicate colloids formed by coprecipitation under various geochemical conditions, i.e. pH, concentration of Al and Si metal ions, ionic strength, and omnipresent cations (Na{sup +}, Ca{sup 2+}, and Mg{sup 2+}). The work is performed by colorimetric method and laser-induced breakdown detection (LIBD). Two consecutive phase separations at 450 nm and 1 kDa are applied to separate the precipitates and colloids from the ionic species. By means of colorimetry, Si and Al can be detected down to 5.8 x10{sup -8} M and 7.4x10{sup -7} M, respectively. On the other hand, LIBD is able to quantify the colloidal size and its number density down to several ppt. Depending on the concentration of Al and Si metal ions, the formation trend of aluminosilicate colloid changes following its solubility curve. The lower the concentration, the higher the pH range in which the colloids start to emerge. Furthermore, the colloids are stable at higher Al and Si concentration and at low ionic strength. In the low pH range, cations provide different effects at low and high ionic strengths. At high ionic strength, the colloids are stable in the presence of a larger cation, while all cations exhibit similar effects at low ionic strength. However, in the high pH range, valence seems to have a stronger effect than ionic radius; colloids are more stable in the presence of monovalent cations than divalent ones. Meanwhile, XRD shows non- and/or poor crystalline structure of the aluminosilicate species. Nevertheless, results from XPS may suggest that the chemical composition (Si/Al ∼ 0.6) of the aluminosilicate precipitates is sillimanite or

  20. Formation mechanisms of metal colloids

    Science.gov (United States)

    Halaciuga, Ionel

    Highly dispersed uniform metallic particles are widely used in various areas of technology and medicine and are likely to be incorporated into many other applications in the future. It is commonly accepted that size, shape and composition of the particles represent critical factors in most applications. Thus, understanding the mechanisms of formation of metal particles and the ways to control the physical (e.g. shape, size) and chemical (e.g. composition) properties is of great importance. In the current research, the formation of uniform silver spheres is investigated experimentally. The parameters that influence the formation of silver particles when concentrated iso-ascorbic acid and silver-polyamine complex solutions are rapidly mixed were studied in the absence of dispersants. We found that by varying the nature of the amine, temperature, concentration of reactants, silver/amine molar ratio, and the nature of the silver salt, the size of the resulting silver particles can be varied in a wide range (0.08--1.5 microm). The silver particles were formed by aggregation of nanosize subunits as substantiated by both electron microscopy and X-ray diffraction techniques and by the vivid rapid color changes during the chemical precipitation process. From the practical standpoint, the goal of this research was to prepare well dispersed spherical silver particles having a relatively smooth surface and a diameter of about 1 microm to satisfy the demands of the current electronic materials market. A two stage particle growth model previously developed to explain the narrow size distribution occurring in synthesis of gold spheres was applied to the present experimental system, and the parameters that control the size distribution characteristics were identified. The kinetic parameter required to match the final particle size was found to be in agreement with the one used previously in modeling formation of gold spheres, suggesting that similar kinetics governs the

  1. Colloidal stability of polymeric nanoparticles in biological fluids

    Energy Technology Data Exchange (ETDEWEB)

    Lazzari, Stefano [ETH Zurich, Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering (Switzerland); Moscatelli, Davide, E-mail: davide.moscatelli@polimi.it [Materiali e Ingegneria Chimica ' Giulio Natta' , Politecnico di Milano, Dipartimento di Chimica (Italy); Codari, Fabio [ETH Zurich, Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering (Switzerland); Salmona, Mario [Istituto di Ricerche Farmacologiche ' Mario Negri' , Department of Molecular Biochemistry and Pharmacology (Italy); Morbidelli, Massimo [ETH Zurich, Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering (Switzerland); Diomede, Luisa [Istituto di Ricerche Farmacologiche ' Mario Negri' , Department of Molecular Biochemistry and Pharmacology (Italy)

    2012-06-15

    Estimating the colloidal stability of polymeric nanoparticles (NPs) in biological environments is critical for designing optimal preparations and to clarify the fate of these devices after administration. To characterize and quantify the physical stability of nanodevices suitable for biomedical applications, spherical NPs composed of poly-lactic acid (PLA) and poly-methyl-methacrylate (PMMA), in the range 100-200 nm, were prepared. Their stability in salt solutions, biological fluids, serum and tissue homogenates was analyzed by dynamic light scattering (DLS). The PMMA NPs remained stable in all fluids, while PLA NPs aggregated in gastric juice and spleen homogenate. The proposed stability test is therefore useful to see in advance whether NPs might aggregate when administered in vivo. To assess colloidal stability ex vivo as well, spectrophotofluorimetric analysis was employed, giving comparable results to DLS.

  2. Formation of gold colloids using thioether derivatives as stabilizing ligands

    NARCIS (Netherlands)

    Li, X.; de Jong, M.R.; Inoue, K.; Huskens, Jurriaan; Shinkai, Seiji; Reinhoudt, David

    2001-01-01

    Thioethers were used as adsorbates for preparing gold nanoparticles. Different thioether derivatives having from 1 to 4 thioether functionalities were synthesized. Colloids were prepared in a two-phase system, and characterized by 1H NMR and transmission electron microscopy (TEM). The stability of

  3. Stabilized super-thermite colloids: A new generation of advanced highly energetic materials

    Science.gov (United States)

    Elbasuney, Sherif; Gaber Zaky, M.; Radwan, Mostafa; Mostafa, Sherif F.

    2017-10-01

    One of the great impetus of nanotechnology on energetic materials is the achievement of nanothermites (metal-oxide/metal) which are characterized by massive heat output. Yet, full exploitation of super-thermites in highly energetic systems has not been achieved. This manuscript reports on the sustainable fabrication of colloidal Fe2O3 and CuO nanoparticles for thermite applications. TEM micrographs demonstrated mono-dispersed Fe2O3 and CuO with an average particle size of 3 and 15 nm respectively. XRD diffractograms demonstrated highly crystalline materials. SEM micrographs demonstrated a great tendency of the developed oxides to aggregate over drying process. The effective integration and dispersion of mono-dispersed colloidal thermite particles into energetic systems are vital for enhanced performance. Aluminum is of interest as highly energetic metal fuel. In this paper, synthesized Fe2O3 and CuO nanoparticles were re-dispersed in isopropyl alcohol (IPA) with aluminum nanoparticles using ultrasonic prope homogenizer. The colloidal thermite peraticles can be intgegrated into highly energetic system for subsequent nanocomposite development. Thanks to stabilization of colloidal CuO nanoparticles in IPA which could offer intimate mixing between oxidizer and metal fuel. The stabilization mechanism of CuO in IPA was correlated to steric stabilization with solvent molecules. This approach eliminated nanoparticle drying and the re-dispersion of dry aggregates into energetic materials. This manuscript shaded the light on the real development of colloidal thermite mixtures and their integration into highly energetic systems.

  4. Designing Whey Protein-Polysaccharide Particles for Colloidal Stability.

    Science.gov (United States)

    Wagoner, Ty; Vardhanabhuti, Bongkosh; Foegeding, E Allen

    2016-01-01

    Interactions between whey proteins and polysaccharides, in particular the formation of food-grade soluble complexes, are of interest because of potential functional and health benefits. A specific application that has not received much attention is the use of complexes for enhanced colloidal stability of protein sols, such as protein-containing beverages. In beverages, the primary goal is the formation of complexes that remain dispersed after thermal processing and extended storage. This review highlights recent progress in the area of forming whey protein-polysaccharide soluble complexes that would be appropriate for beverage applications. Research in this area indicates that soluble complexes can be formed and stabilized that are reasonably small in size and possess a large surface charge that would predict colloidal stability. Selection of specific proteins and polysaccharides can be tailored to desired conditions. The principal challenges involve overcoming restrictions on protein concentration and ensuring that protein remains bioavailable.

  5. A colloidal singularity reveals the crucial role of colloidal stability for nanomaterials in-vitro toxicity testing: nZVI-microalgae colloidal system as a case study.

    Directory of Open Access Journals (Sweden)

    Soledad Gonzalo

    Full Text Available Aggregation raises attention in Nanotoxicology due to its methodological implications. Aggregation is a physical symptom of a more general physicochemical condition of colloidal particles, namely, colloidal stability. Colloidal stability is a global indicator of the tendency of a system to reduce its net surface energy, which may be achieved by homo-aggregation or hetero-aggregation, including location at bio-interfaces. However, the role of colloidal stability as a driver of ENM bioactivity has received little consideration thus far. In the present work, which focuses on the toxicity of nanoscaled Fe° nanoparticles (nZVI towards a model microalga, we demonstrate that colloidal stability is a fundamental driver of ENM bioactivity, comprehensively accounting for otherwise inexplicable differential biological effects. The present work throws light on basic aspects of Nanotoxicology, and reveals a key factor which may reconcile contradictory results on the influence of aggregation in bioactivity of ENMs.

  6. Rheology of stabilized cerium-gadolinium oxide (CGO) colloidal system

    DEFF Research Database (Denmark)

    Marani, Debora; Hjelm, Johan; Wandel, Marie

    Achievement of stable dispersion with high solid loadings and low viscosity is crucial issue in ceramic films processing. In this work, systematic analysis of the rheological properties of CGO colloidal suspension was performed. The study aimed to define methods for evaluating fully stabilized...... conditions and critical parameters. The influences of dispersant and inorganic contents on suspensions properties were investigated. The optimization of dispersant content was achieved by studying flow behaviour of suspensions at different amounts of dispersant. Rotational and oscillatory tests were...

  7. Colloidal stability and chemical reactivity of complex colloids containing Fe³⁺.

    Science.gov (United States)

    van Leeuwen, Y M; Velikov, K P; Kegel, W K

    2014-07-15

    The reactivity of iron contained within insoluble colloidal metal-pyrophosphate salts was determined and compared to the reactivity of a soluble iron salt (FeCl3). As a model system for the reactivity of iron in food products, the formation of an iron-polyphenol complex was followed with spectrophotometry. Three types of systems were prepared and their colloidal stability and reactivity studied: Fe(3+) pyrophosphate, protein-coated Fe(3+) pyrophosphate and mixed-metal pyrophosphates containing Fe(3+) and a second cation M. The additional cation used was either monovalent (sodium) or divalent (M(2+)). It was found that: (i) incorporating iron in a colloidal salt reduced its reactivity compared to free Fe(3+) ions; (ii) coating the particles with a layer of hydrophobic protein (zein) increased stability and further decreased the reactivity. Finally, the most surprising result was that (iii) a mixed system containing more Fe(3+) than M actually increased the reactivity of the contained iron, while the reverse, a system containing excess M, inhibited the reactivity completely.

  8. Stability of orientationally disordered crystal structures of colloidal hard dumbbells.

    Science.gov (United States)

    Marechal, Matthieu; Dijkstra, Marjolein

    2008-06-01

    We study the stability of orientationally disordered crystal phases in a suspension of colloidal hard dumbbells using Monte Carlo simulations. For dumbbell bond length L/sigmafcc structure for a large part of the stable plastic crystal regime. In addition, we study the stability of an orientationally disordered aperiodic crystal structure in which the spheres of the dumbbells are on a random-hexagonal-close-packed lattice, and the dumbbells are formed by taking random pairs of neighboring spheres. Using free-energy calculations, we determine the fluid-aperiodic crystal and periodic-aperiodic crystal coexistence regions for L/sigma>0.88 .

  9. Addressing Colloidal Stability for Unambiguous Electroanalysis of Single Nanoparticle Impacts.

    Science.gov (United States)

    Robinson, Donald A; Kondajji, Aditya M; Castañeda, Alma D; Dasari, Radhika; Crooks, Richard M; Stevenson, Keith J

    2016-07-01

    Herein the problem of colloidal instability on electrochemically detected nanoparticle (NP) collisions with a Hg ultramicroelectrode (UME) by electrocatalytic amplification is addressed. NP tracking analysis (NTA) shows that rapid aggregation occurs in solution after diluting citrate-stabilized Pt NPs with hydrazine/phosphate buffers of net ionic strength greater than 70 mM. Colloidal stability improves by lowering the ionic strength, indicating that aggregation processes were strongly affected by charge screening of the NP double layer interactions at high cation concentrations. For the system of lowest ionic strength, the overwhelming majority of observed electrocatalytic current signals represent single NP/electrode impacts, as confirmed by NTA kinetic monitoring. NP diffusion coefficients determined by NTA and NP impact electroanalysis are in excellent agreement for the stable colloids, which signifies that the sticking probability of Pt NPs interacting with Hg is unity and that the observed NP impact rate agrees with the expected steady-state diffusive flux expression for the spherical cap Hg UME.

  10. Domain and droplet sizes in emulsions stabilized by colloidal particles

    Science.gov (United States)

    Frijters, Stefan; Günther, Florian; Harting, Jens

    2014-10-01

    Particle-stabilized emulsions are commonly used in various industrial applications. These emulsions can present in different forms, such as Pickering emulsions or bijels, which can be distinguished by their different topologies and rheology. We numerically investigate the effect of the volume fraction and the uniform wettability of the stabilizing spherical particles in mixtures of two fluids. For this, we use the well-established three-dimensional lattice Boltzmann method, extended to allow for the added colloidal particles with non-neutral wetting properties. We obtain data on the domain sizes in the emulsions by using both structure functions and the Hoshen-Kopelman (HK) algorithm, and we demonstrate that both methods have their own (dis)advantages. We confirm an inverse dependence between the concentration of particles and the average radius of the stabilized droplets. Furthermore, we demonstrate the effect of particles detaching from interfaces on the emulsion properties and domain-size measurements.

  11. Stability studies of colloidal silica dispersions in binary solvent mixtures

    CERN Document Server

    Bean, K H

    1997-01-01

    A series of monodispersed colloidal silica dispersions, of varying radii, has been prepared. These particles are hydrophilic in nature due to the presence of surface silanol groups. Some of the particles have been rendered hydrophobic by terminally grafting n-alkyl (C sub 1 sub 8) chains to the surface. The stability of dispersions of these various particles has been studied in binary mixtures of liquids, namely (i) ethanol and cyclohexane, and (ii) benzene and n-heptane. The ethanol - cyclohexane systems have been studied using a variety of techniques. Adsorption excess isotherms have been established and electrophoretic mobility measurements have been made. The predicted stability of the dispersions from D.V.L.O. calculations is compared to the observed stability. The hydrophilic silica particles behave as predicted by the calculations, with the zeta potential decreasing and the van der Waals attraction increasing with increasing cyclohexane concentration. The hydrophobic particles behave differently than e...

  12. Multiple Colors Output on Voile through 3D Colloidal Crystals with Robust Mechanical Properties.

    Science.gov (United States)

    Meng, Yao; Tang, Bingtao; Ju, Benzhi; Wu, Suli; Zhang, Shufen

    2017-01-25

    Distinguished from the chromatic mechanism of dyes and pigments, structural color is derived from physical interactions of visible light with structures that are periodic at the scale of the wavelength of light. Using colloidal crystals with coloring functions for fabrics has resulted in significant improvements compared with chemical colors because the structural color from colloidal crystals bears many unique and fascinating optical properties, such as vivid iridescence and nonphotobleaching. However, the poor mechanical performance of the structural color films cannot meet actual requirements because of the weak point contact of colloidal crystal particles. Herein, we demonstrate in this study the patterning on voile fabrics with high mechanical strength on account of the periodic array lock effect of polymers, and multiple structural color output was simultaneously achieved by a simple two-phase self-assembly method for printing voile fabrics with 3D colloidal crystals. The colored voile fabrics exhibit high color saturation, good mechanical stability, and multiple-color patterns printable. In addition, colloidal crystals are promising potential substitutes for organic dyes and pigments because colloidal crystals are environmentally friendly.

  13. Pickering emulsions stabilized by oppositely charged colloids: Stability and pattern formation

    Science.gov (United States)

    Christdoss Pushpam, Sam David; Basavaraj, Madivala G.; Mani, Ethayaraja

    2015-11-01

    A binary mixture of oppositely charged colloids can be used to stabilize water-in-oil or oil-in-water emulsions. A Monte Carlo simulation study to address the effect of charge ratio of colloids on the stability of Pickering emulsions is presented. The colloidal particles at the interface are modeled as aligned dipolar hard spheres, with attractive interaction between unlike-charged and repulsive interaction between like-charged particles. The optimum composition (fraction of positively charged particles) required for the stabilization corresponds to a minimum in the interaction energy per particle. In addition, for each charge ratio, there is a range of compositions where emulsions can be stabilized. The structural arrangement of particles or the pattern formation at the emulsion interface is strongly influenced by the charge ratio. We find well-mixed isotropic, square, and hexagonal arrangements of particles on the emulsion surface for different compositions at a given charge ratio. The distribution of coordination numbers is calculated to characterize structural features. The simulation study is useful for the rational design of Pickering emulsifications wherein oppositely charged colloids are used, and for the control of pattern formation that can be useful for the synthesis of colloidosomes and porous shells derived thereof.

  14. Synthesis and performance of colloidal silica nano-abrasives with controllable size for chemical mechanical planarization.

    Science.gov (United States)

    Zhang, K L; Song, Z T; Wang, F; Wang, L Y; Feng, S L

    2009-02-01

    Under the analysis of particle growth mechanism, the monodisperse colloidal silica abrasives for chemical mechanical planarization (CMP) slurry were synthesized by the modified ion-exchanged and hydrothermal step-polymerization process. After the colloidal silica with controllable size was synthesized, its microstructure, stability and CMP performance was characterized and tested by SEM, HRTEM, Zeta potential Analyzer and CMP tester. Results show that the spherical, high stable (Zeta potential: -52.8 mV) colloidal silica with controllable size was achieved. About its CMP performance, the polishing rate for silicon double-side CMP is increased to be 317 nm/min and the polished surface roughness (RMS) was reduced to 0.32 nm.

  15. Dispersion stability and electrokinetic properties of intrinsic plutonium colloids: implications for subsurface transport.

    Science.gov (United States)

    Abdel-Fattah, Amr I; Zhou, Dongxu; Boukhalfa, Hakim; Tarimala, Sowmitri; Ware, S Doug; Keller, Arturo A

    2013-06-04

    Subsurface transport of plutonium (Pu) may be facilitated by the formation of intrinsic Pu colloids. While this colloid-facilitated transport is largely governed by the electrokinetic properties and dispersion stability (resistance to aggregation) of the colloids, reported experimental data is scarce. Here, we quantify the dependence of ζ-potential of intrinsic Pu(IV) colloids on pH and their aggregation rate on ionic strength. Results indicate an isoelectric point of pH 8.6 and a critical coagulation concentration of 0.1 M of 1:1 electrolyte at pH 11.4. The ζ-potential/pH dependence of the Pu(IV) colloids is similar to that of goethite and hematite colloids. Colloid interaction energy calculations using these values reveal an effective Hamaker constant of the intrinsic Pu(IV) colloids in water of 1.85 × 10(-19) J, corresponding to a relative permittivity of 6.21 and refractive index of 2.33, in agreement with first principles calculations. This relatively high Hamaker constant combined with the positive charge of Pu(IV) colloids under typical groundwater aquifer conditions led to two contradicting hypotheses: (a) the Pu(IV) colloids will exhibit significant aggregation and deposition, leading to a negligible subsurface transport or (b) the Pu(IV) colloids will associate with the relatively stable native groundwater colloids, leading to a considerable subsurface transport. Packed column transport experiments supported the second hypothesis.

  16. Sterically Stabilized Poly(3,4-ethylenedioxythiophene) Colloidal Dispersions Doped with Different Sulfonic Acids

    Institute of Scientific and Technical Information of China (English)

    Tie Jun WANG; Ping CHEN; Xiu Jie HU; Shu Yun ZHOU

    2006-01-01

    The preparation of sterically stabilized poly(3, 4-ethylenedioxythiophene)(PEDOT)colloidal dispersions doped with different sulfonic acids is described. Three different sulfonic acids, i.e., p-toluenesulfonic acid, β-naphthalenesuffonic acid and D-camphor-10-sulfonic acid are used, facilitating the preparation of sterically stable PEDOT colloidal particles. The influences of the dopants and concentration of polymeric stabilizer on the yields, morphologies and electrical properties of the resultant colloidal particles were investigated. The colloidal particles with the size ranging from 172 to 334 nm have been obtained in good yields. The compressed pellet conductivity was as high as 4.5 Scm-1.

  17. Gelation mechanism of cellulose nanofibre gels: A colloids and interfacial perspective.

    Science.gov (United States)

    Mendoza, Llyza; Batchelor, Warren; Tabor, Rico F; Garnier, Gil

    2017-09-01

    Nanocellulose gels form a new category of sustainable soft materials of industrial interest for a wide range of applications. There is a need to map the rheological properties and understand the mechanism which provides the colloidal stability and gelation of these nanofibre suspensions. TEMPO (2,2,6,6,-tetramethylpiperidine-1-oxyl)-oxidised cellulose nanofibre gels were investigated at different fibre concentrations, pH and ionic strength. Dynamic and cyclic rheological studies was performed to quantify gel behaviour and properties. Gels were produced at different pH and salt contents to map and understand colloidal stability of the nanocellulose gel. Rheology indicates gelation asa transitionary state starting at a fibre concentration of 0.1wt.%. The colloidal stability of the nanocellulose gel network is controlled by pH and salt, whereas fibre concentration mainly dictates the dynamic rheological properties. Decreasing pH and adding salt destabilises the gel network by eluting bound water which is correlated with the decrease in electrostatic repulsion between fibres. The gelation and colloidal stability of these nanocellulose gels is driven by electrostatic forces and the entanglement ability of the fibrous system to overlap. Crown Copyright © 2017. Published by Elsevier Inc. All rights reserved.

  18. CATALYTIC PROPERTIES OF POLYMER-STABILIZED COLLOIDAL METAL NANOPARTICLES SYNTHESIZED BY MICROWAVE IRRADIATION

    Institute of Scientific and Technical Information of China (English)

    Wei-xia Tu; Bao-lin He; Han-fan Liu; Xue-lan Luo; Xun Liang

    2005-01-01

    Catalytic properties of polymer-stabilized colloidal metal nanoparticles synthesized by microwave irradiation were studied in the selective hydrogenation of unsaturated aldehydes, o-chloronitrobenzene and the hydrogenation of alkenes. The results show that nanosized metal particles synthesized by microwave irradiation have similar catalytic performance in selective hydrogenation of unsaturated aldehydes, better selectivity to o-chloroaniline in hydrogenation of o-chloronitrobenzene and higher catalytic activities in hydrogenation of alkenes, compared with metal clusters prepared by conventional heating. The same apparent activation energy (Ea = 29 kJ mol-1) for hydrogenation of 1-heptene catalyzed with platinum nanoparticles prepared by both heating modes implied that the reaction followed the same mechanism.

  19. Stability of colloidal silver nanoparticles trapped in lipid bilayer: effect of lecithin concentration and applied temperature

    NARCIS (Netherlands)

    Barani, H.; Montazer, M.; Braun, H.G.; Dutschk, Victoria

    2014-01-01

    The use of silver nanoparticle on various substrates has been widespread because of its good antibacterial properties that directly depend on the stability of the silver nanoparticles in a colloidal suspension. In this study, the colloidal solutions of the silver nanoparticles were synthesised by a

  20. Stability of colloidal silver nanoparticles trapped in lipid bilayer: effect of lecithin concentration and applied temperature

    NARCIS (Netherlands)

    Barani, H.; Montazer, M.; Braun, H.G.; Dutschk, V.

    2014-01-01

    The use of silver nanoparticle on various substrates has been widespread because of its good antibacterial properties that directly depend on the stability of the silver nanoparticles in a colloidal suspension. In this study, the colloidal solutions of the silver nanoparticles were synthesised by a

  1. Colloidal Stability of Graphene Oxide Nanosheets in Aqueous Solutions

    Science.gov (United States)

    Guikema, Janice; Wang, Yung-Li; Chen, Kai

    2013-03-01

    Carbon-based nanomaterials are increasingly used in commercial products as well as in research and industrial applications. Due to its extraordinary properties, graphene has attracted intense research interest and has been demonstrated in many potential applications including solar cells, conductive ink, and transistors. Graphene oxide has also been studied extensively and has been used to produce biocompatible antibacterial paper. Chemical reduction of graphene oxide is commonly used to produce inexpensive graphene in large quantities. With the increasing use of graphene and graphene oxide in consumer products, these nanomaterials may inevitably be released to aqueous systems, resulting in potential risk to environmental ecosystems and human health. The fate and mobility of graphene and its oxides in aquatic systems is dependent on their colloidal stability. We will discuss our study of the early-stage aggregation kinetics of graphene oxide in aqueous solutions. We prepared a suspension of single-layer graphene oxide nanosheets in water and used time-resolved dynamic light scattering to study the influence of electrolytes and pH on the aggregation kinetics of the nanosheets. Atomic force microscopy was employed to further examine the graphene oxide nanosheets.

  2. Effect of Gd3+ on the colloidal stability of liposomes.

    Science.gov (United States)

    Sabín, Juan; Prieto, Gerardo; Sennato, Simona; Ruso, Juan M; Angelini, Roberta; Bordi, Federico; Sarmiento, Félix

    2006-09-01

    Lanthanide ions such as La3+ and Gd3+ are well known to have large effects on the structure of phospholipid membranes. Unilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) were prepared by sonication method and confirmed by transmission electron microscopy. The effects of concentration of gadolinium ions Gd3+ on DPPC unilamellar vesicles in aqueous media were studied by different techniques. As physical techniques, photon correlation spectroscopy, electrophoretic mobility, and differential scanning calorimetry were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersities values were observed as Gd3+ concentration increases, suggesting that this cation induces the aggregation of vesicles. Electrophoretic mobility measurements on unilamellar vesicles as a function of Gd3+ ion concentration show that the vesicles adsorb Gd3+ ions. Above Gd3+ concentrations of 0.1 mol dm-3, the zeta potential and light scattering measurements indicate the beginning of aggregation process. For comparison with similar phospholipids, the zeta potential of phosphatidylcholine interacting with Gd3+ was measured, showing an analogous behavior. Differential scanning calorimetry has been used to determine the effect of Gd3+ on the transition temperature (Tc) and on the enthalpy (DeltaHc) associated with the process.

  3. Protein-silver nanoparticle interactions to colloidal stability in acidic environments.

    Science.gov (United States)

    Tai, Jui-Ting; Lai, Chao-Shun; Ho, Hsin-Chia; Yeh, Yu-Shan; Wang, Hsiao-Fang; Ho, Rong-Ming; Tsai, De-Hao

    2014-11-04

    We report a kinetic study of Ag nanoparticles (AgNPs) under acidic environments (i.e., pH 2.3 to pH ≈7) and systematically investigate the impact of protein interactions [i.e., bovine serum albumin (BSA) as representative] to the colloidal stability of AgNPs. Electrospray-differential mobility analysis (ES-DMA) was used to characterize the particle size distributions and the number concentrations of AgNPs. Transmission electron microscopy was employed orthogonally to provide visualization of AgNPs. For unconjugated AgNPs, the extent of aggregation, or the average particle size, was shown to be increased significantly with an increase of acidity, where a partial coalescence was found between the primary particles of unconjugated AgNP clusters. Aggregation rate constant, kD, was also shown to be proportional to acidity, following a correlation of log(kD) = -1.627(pH)-9.3715. Using ES-DMA, we observe BSA had a strong binding affinity (equilibrium binding constant, ≈ 1.1 × 10(6) L/mol) to the surface of AgNPs, with an estimated maximum molecular surface density of ≈0.012 nm(-2). BSA-functionalized AgNPs exhibited highly-improved colloidal stability compared to the unconjugated AgNPs under acidic environments, where both the acid-induced interfacial dissolution and the particle aggregation became negligible. Results confirm a complex mechanism of colloidal stability of AgNPs: the aggregation process was shown to be dominant, and the formation of BSA corona on AgNPs suppressed both particle aggregation and interfacial dissolution of AgNP samples under acidic environments.

  4. On the effect of Ca2+ and La3+ on the colloidal stability of liposomes.

    Science.gov (United States)

    Sabín, Juan; Prieto, Gerardo; Messina, Paula V; Ruso, Juan M; Hidalgo-Alvarez, Roque; Sarmiento, Félix

    2005-11-22

    This work deals with the effect of Ca2+ and La3+ on the colloidal stability of phosphatidylcholine (PC) liposomes in aqueous media. As physical techniques, nephelometry, photon correlation spectroscopy, electrophoretic mobility, and surface tension were used. The theoretical predictions of the colloidal stability of liposomes were followed using the Derjaguin-Landau-Verwey-Overbeek theory. Changes in the size of liposomes and high polydispersity values were observed as La3+ concentration increases, suggesting that this cation induces the aggregation of liposomes. However, changes in polydispersity were not observed with Ca2+, suggesting a coalescence mechanism or fusion of liposomes. The stability factor (W), calculated from the nephelometry measurements indicated that aggregation/fusion occurs at a critical concentration (c.c.) of 0.3 and 0.7 M for La3+ and Ca2+, respectively. To gain a better insight into the interaction mechanism between the liposomes and the studied ions, the interaction between PC monolayers and Ca2+ and La3+ was studied. Changes in the surface area per lipid molecule (A0) in the monolayer at the c.c. values were found for both ions, with a more pronounced effect in the case of Ca2+. This corresponds with a larger reduction of the steric repulsive interaction between the headgroups at the phospholipid membrane (pi(head)). The experimental result validates the hypothesis made on the liposome fusion in the presence of Ca2+ and liposome aggregation in the presence of La3+. These aggregation mechanisms have also been confirmed by transmission electron microscopy.

  5. Silver nanoparticle colloids with γ-cyclodextrin: enhanced stability and Gibbs–Marangoni flow

    Energy Technology Data Exchange (ETDEWEB)

    Amiri, Setareh; Duroux, Laurent; Larsen, Kim Lambertsen, E-mail: kll@bio.aau.dk [Aalborg University, Department of Chemistry and Bioscience (Denmark)

    2015-01-15

    Although cyclodextrins (CD) are effective stabilizers for metal nanoparticle colloids, differences between α-, β- and γ-CD in stabilizing such colloids have not been previously reported. In this study, silver nanoparticles (AgNP) were synthesized using NaBH{sub 4} as reducing agent and cyclodextrins as stabilizers. Long-term stability of AgNP colloids in equilibrium conditions showed no marked differences between CD types. Transmission electron microscopy and quantitative image analysis revealed only marginal differences in particle sizes for CD-AgNP, although statistically significant. CD-AgNP colloids showed dispersed particles with average diameters of 7.3 ± 2.2, 6.3 ± 2.9 and 4.9 ± 1.9 nm for α-, β- and γ-CD, respectively, and with similar ζ-potentials about −25 to −30 mV. AgNP without CD showed bigger and aggregated particles of 15.0 ± 2.0 nm with lower ζ-potentials of about −40 mV. When subjected to centrifugal forces, i.e. non-equilibrium conditions, γ-CD was markedly more efficient than α- and β-CD in stabilizing the colloids. Drying patterns of colloid droplets showed a typical self-pinned coffee ring for all but the colloid stabilized by γ-CD, which showed a pattern resulting from a dominant Gibbs–Marangoni flow inside the drying droplet. Calculations using the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory supported the stabilizing effect of CD in equilibrium conditions; it however did not provide clues for the superior stabilization by γ-CD in conditions of hydrodynamic stress.

  6. Colloidal stability and chemical reactivity of complex colloids containing Fe3+

    NARCIS (Netherlands)

    van Leeuwen, Y.M.|info:eu-repo/dai/nl/314850139; Velikov, K. P.; Kegel, W.K.|info:eu-repo/dai/nl/113729464

    2014-01-01

    The reactivity of iron contained within insoluble colloidal metal-pyrophosphate salts was determined and compared to the reactivity of a soluble iron salt (FeCl3). As a model system for the reactivity of iron in food products, the formation of an iron–polyphenol complex was followed with

  7. SYNTHESIS OF POLYMER-STABILIZED RUTHENIUM COLLOIDS BY LOW BOILING POINT ALCOHOL REDUCTION

    Institute of Scientific and Technical Information of China (English)

    Ya-li Su; Xiu-ru Li; Yue-jin Tong; Yue-sheng Li

    2003-01-01

    Stable and well-dispersed poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium colloidal clusters were prepared via the reduction of ruthenium(Ⅲ) chloride by refluxing with low boiling point alcohols. Investigation of the size of Ru colloids by transmission electron microscopy (TEM) indicated that the average diameters could be controlled in the range of 1.2-1.6 nm with relative standard deviations of less than 0.33 by changing the molar ratio of PVP to Ru. The X-ray photoelectron spectroscopy (XPS) characterization verified the formation of elemental ruthenium colloids.

  8. Control and formation mechanism of extended nanochannel geometry in colloidal mesoporous silica particles.

    Science.gov (United States)

    Sokolov, I; Kalaparthi, V; Volkov, D O; Palantavida, S; Mordvinova, N E; Lebedev, O I; Owens, J

    2017-01-04

    A large class of colloidal multi-micron mesoporous silica particles have well-defined cylindrical nanopores, nanochannels which self-assembled in the templated sol-gel process. These particles are of broad interest in photonics, for timed drug release, enzyme stabilization, separation and filtration technologies, catalysis, etc. Although the pore geometry and mechanism of pore formation of such particles has been widely investigated at the nanoscale, their pore geometry and its formation mechanism at a larger (extended) scale is still under debate. The extended geometry of nanochannels is paramount for all aforementioned applications because it defines accessibility of nanochannels, and subsequently, kinetics of interaction of the nanochannel content with the particle surrounding. Here we present both experimental and theoretical investigation of the extended geometry and its formation mechanism in colloidal multi-micron mesoporous silica particles. We demonstrate that disordered (and consequently, well accessible) nanochannels in the initially formed colloidal particles gradually align and form extended self-sealed channels. This knowledge allows to control the percentage of disordered versus self-sealed nanochannels, which defines accessibility of nanochannels in such particles. We further show that the observed aligning the channels is in agreement with theory; it is thermodynamically favored as it decreases the Gibbs free energy of the particles. Besides the practical use of the obtained results, developing a fundamental understanding of the mechanisms of morphogenesis of complex geometry of nanopores will open doors to efficient and controllable synthesis that will, in turn, further fuel the practical utilization of these particles.

  9. Electrophoresis in charge-stabilized colloidal cluster phases.

    Science.gov (United States)

    Groenewold, Jan; Zhang, Tianhui; Kegel, Willem K

    2011-06-09

    The reversible properties of cluster phases have been described by theories that invoke Coulomb interactions as a stabilizing mechanism. What is lacking so far is direct measurement of these charges. This contribution aims at predicting what to expect if electrophoresis measurements were to be performed on these systems. As a result, we get a picture that exhibits several interesting features: (1) The existence of monomers and clusters lead to distinctly different mobilities (zeta potentials) in a single sample. (2) Strong dependence of the mobilities on particle volume fraction. It is our aim that the theory outlined in this paper may serve as a guideline to interpret the expectedly "messy" electrophoretic measurements.

  10. Synthesis of Monodispersed Gold Nanoparticles with Exceptional Colloidal Stability with Grafted Polyethylene Glycol-g-polyvinyl Alcohol

    Directory of Open Access Journals (Sweden)

    Alaaldin M. Alkilany

    2015-01-01

    Full Text Available Herein, we report the synthesis of spherical gold nanoparticles with tunable core size (23–79 nm in the presence of polyethylene glycol-g-polyvinyl alcohol (PEG-g-PVA grafted copolymer as a reducing, capping, and stabilizing agent in a one-step protocol. The resulted PEG-g-PVA-capped gold nanoparticles are monodispersed with an exceptional colloidal stability against salt addition, repeated centrifugation, and extensive dialysis. The effect of various synthesis parameters and the kinetic/mechanism of the nanoparticle formation are discussed.

  11. Experimental and theoretical studies of the colloidal stability of nanoparticles-a general interpretation based on stability maps.

    Science.gov (United States)

    Segets, Doris; Marczak, Renata; Schäfer, Stefan; Paula, Carolin; Gnichwitz, Jan-Frederik; Hirsch, Andreas; Peukert, Wolfgang

    2011-06-28

    The current work addresses the understanding of the stabilization of nanoparticles in suspension. Specifically, we study ZnO in ethanol for which the influence of particle size and reactant ratio as well as surface coverage on colloidal stability in dependence of the purification progress was investigated. The results revealed that the well-known ζ-potential determines not only the colloidal stability but also the surface coverage of acetate groups bound to the particle surface. The acetate groups act as molecular spacers between the nanoparticles and prevent agglomeration. Next to DLVO calculations based on the theory of Derjaguin, Landau, Verwey and Overbeek using a core-shell model we find that the stability is better understood in terms of dimensionless numbers which represent attractive forces as well as electrostatic repulsion, steric effects, transport properties, and particle concentration. Evaluating the colloidal stability in dependence of time by means of UV-vis absorption measurements a stability map for ZnO is derived. From this map it becomes clear that the dimensionless steric contribution to colloidal stability scales with a stability parameter including dimensionless repulsion and attraction as well as particle concentration and diffusivity of the particles according to a power law with an exponent of -0.5. Finally, we show that our approach is valid for other stabilizing molecules like cationic dendrons and is generally applicable for a wide range of other material systems within the limitations of vanishing van der Waals forces in refractive index matched situations, vanishing ζ-potential and systems without a stabilizing shell around the particle surface.

  12. In vitro hyperthermia with improved colloidal stability and enhanced SAR of magnetic core/shell nanostructures.

    Science.gov (United States)

    Patil, R M; Thorat, N D; Shete, P B; Otari, S V; Tiwale, B M; Pawar, S H

    2016-02-01

    Magnetic core/shell nanostructures of Fe3O4 nanoparticles coated with oleic acid and betaine-HCl were studied for their possible use in magnetic fluid hyperthermia (MFH). Their colloidal stability and heat induction ability were studied in different media viz. phosphate buffer solution (PBS), saline solution and glucose solution with different physiological conditions and in human serum. The results showed enhanced colloidal stability in these media owing to their high zeta potential values. Heat induction studies showed that specific absorption rates (SAR) of core/shells were 82-94W/g at different pH of PBS and concentrations of NaCl and glucose. Interestingly, core/shells showed 78.45±3.90W/g SAR in human serum. The cytotoxicity of core/shells done on L929 and HeLa cell lines using 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide and trypan blue dye exclusion assays showed >89% and >80% cell viability for 24 and 48h respectively. Core/shell structures were also found to be very efficient for in vitro MFH on cancer cell line. About 95% cell death was occurred in 90min after hyperthermia treatment. The mechanism of cell death was found to be elevated ROS generation in cells after exposure to core/shells in external magnetic field. This study showed that these core/shells have a great potential to be used in in vivo MFH. Copyright © 2015 Elsevier B.V. All rights reserved.

  13. Degradation Mechanisms of Colloidal Organic Matter in Biofilm Reactors

    DEFF Research Database (Denmark)

    Larsen, Tove; Harremoës, Poul

    1994-01-01

    The degradation mechanisms of colloidal organic matter in biofilm reactors have been studied in an idealized laboratory reactor system with soluble starch as a model substrate. Batch tests and experiments with different reactor configurations have shown that for this specific substrate, bulk liquid......-diffusible organic matter in a biofilm reactor. DH depends on the combined volumetric and surface hydraulic loading rate, Q2/(AV). In full-scale wastewater treatment plants, the degradation mechanism presented in this paper can explain important differences between the performance of trickling filters and RBC...... hydrolysis is the mechanism for transforming non-diffusible organic matter into biofilm diffusible substrate. A simplified mathematical description has led to the identification of the degree of hydrolysis, DH, as the parameter expressing the major difference between degradation of diffusible and non...

  14. Using state diagrams for predicting colloidal stability of whey protein beverages.

    Science.gov (United States)

    Wagoner, Ty B; Ward, Loren; Foegeding, E Allen

    2015-05-06

    A method for evaluating aspects of colloidal stability of whey protein beverages after thermal treatment was established. Three state diagrams for beverages (pH 3-7) were developed representing protein solubility, turbidity, and macroscopic state after two ultrahigh-temperature (UHT) treatments. Key transitions of stability in the state diagrams were explored using electrophoresis and chromatography to determine aggregation propensities of β-lactoglobulin, α-lactalbumin, bovine serum albumin, and glycomacropeptide. The state diagrams present an overlapping view of high colloidal stability at pH 3 accompanied by high solubility of individual whey proteins. At pH 5, beverages were characterized by poor solubility, high turbidity, and aggregation/gelation of whey proteins with the exception of glycomacropeptide. Stability increased at pH 6, due to increased solubility of α-lactalbumin. The results indicate that combinations of state diagrams can be used to identify key regions of stability for whey protein containing beverages.

  15. Preparation of poly(N-vinylpyrrolidone-stabilized ZnO colloid nanoparticles

    Directory of Open Access Journals (Sweden)

    Tatyana Gutul

    2014-04-01

    Full Text Available We propose a method for the synthesis of a colloidal ZnO solution with poly(N-vinylpyrrolidone (PVP as stabilizer. Stable colloidal solutions with good luminescence properties are obtained by using PVP as stabilizer in the synthesis of ZnO nanoparticles by a sol–gel method assisted by ultrasound. Nanoparticles with sizes of 30–40 nm in a PVP matrix are produced as a solid product. The colloidal ZnO/PVP/methanol solution, apart from the most intense PL band at 356 nm coming from the PVP, exhibits a strong PL band at 376 nm (3.30 eV which corresponds to the emission of the free exciton recombination in ZnO nanoparticles.

  16. Adsorption of polyelectrolytes and charged block copolymers on oxides consequences for colloidal stability

    NARCIS (Netherlands)

    Hoogeveen, N.G.

    1996-01-01


    The aim of the study described in this thesis was to examine the adsorption properties of polyelectrolytes and charged block copolymers on oxides, and the effect of these polymers on the colloidal stability of oxidic dispersions. For this purpose the interaction of some well-characterised

  17. Spontaneous oil-in-water emulsification induced by charge-stabilized dispersions of various inorganic colloids

    NARCIS (Netherlands)

    Sacanna, S.|info:eu-repo/dai/nl/311471676; Kegel, W.K.|info:eu-repo/dai/nl/113729464; Philipse, A.P.|info:eu-repo/dai/nl/073532894

    2007-01-01

    Charge-stabilized dispersions of inorganic colloids are shown to induce spontaneous emulsification of hydrophobic (TPM) molecules to stable oil-in-water emulsions, with monodisperse, mesoscopic oil droplet diameters in the range of 30-150 nm, irrespective of the polydispersity of the starting

  18. Adsorption of polyelectrolytes and charged block copolymers on oxides. Consequences for colloidal stability.

    NARCIS (Netherlands)

    Hoogeveen, N.G.

    1996-01-01

    The aim of the study described in this thesis was to examine the adsorption properties of polyelectrolytes and charged block copolymers on oxides, and the effect of these polymers on the colloidal stability of oxidic dispersions. For this purpose the interaction of some well-characterised polyelectr

  19. Pickering emulsions: Wetting and colloidal stability of hairy particles - A self-consistent field theory

    NARCIS (Netherlands)

    Salari, J.W.O.; Leermakers, F.A.M.; Klumperman, B.

    2011-01-01

    The assembly of sterically stabilized colloids at liquid–liquid interfaces is studied with the self-consistent field (SCF) theory using the discretization scheme that was developed by Scheutjens, Fleer, and co-workers. The model is based on a poly(methyl methacrylate) (pMMA) particle with poly(isobu

  20. Statistical mechanics of DNA-mediated colloidal aggregation.

    Science.gov (United States)

    Licata, Nicholas A; Tkachenko, Alexei V

    2006-10-01

    We present a statistical mechanical model of aggregation in colloidal systems with DNA-mediated interactions. We obtain a general result for the two-particle binding energy in terms of the hybridization free energy DeltaG of DNA and two model-dependent properties: the average number of available DNA bridges and the effective DNA concentration c(eff). We calculate these parameters for a particular DNA bridging scheme. The fraction of all the n-mers, including the infinite aggregate, are shown to be universal functions of a single parameter directly related to the two-particle binding energy. We explicitly take into account the partial ergodicity of the problem resulting from the slow DNA binding-unbinding dynamics, and introduce the concept of angular localization of DNA linkers. In this way, we obtain a direct link between DNA thermodynamics and the global aggregation and melting properties in DNA-colloidal systems. The results of the theory are shown to be in quantitative agreement with two recent experiments with particles of micron and nanometer size.

  1. Colloidal stability of tannins: astringency, wine tasting and beyond

    Science.gov (United States)

    Zanchi, D.; Poulain, C.; Konarev, P.; Tribet, C.; Svergun, D. I.

    2008-12-01

    Tannin-tannin and tannin-protein interactions in water-ethanol solvent mixtures are studied in the context of red wine tasting. While tannin self-aggregation is relevant for the visual aspect of wine tasting (limpidity and related colloidal phenomena), tannin affinities for salivary proline-rich proteins is fundamental for a wide spectrum of organoleptic properties related to astringency. Tannin-tannin interactions are analyzed in water-ethanol wine-like solvents and the precipitation map is constructed for a typical grape tannin. The interaction between tannins and human salivary proline-rich proteins (PRP) are investigated in the framework of the shell model for micellization, known for describing tannin-induced aggregation of β-casein. Tannin-assisted micellization and compaction of proteins observed by SAXS are described quantitatively and discussed in the case of astringency.

  2. Colloidal stability of tannins: astringency, wine tasting and beyond

    Energy Technology Data Exchange (ETDEWEB)

    Zanchi, D; Poulain, C [Laboratoire de Physique Theorique et Hautes Energies, 4 Place Jussieu, BP 126, F-75252 Paris Cedex 05 (France); Konarev, P; Svergun, D I [European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, D-22603 Hamburg (Germany); Tribet, C [Physico-Chimie des Polymeres et Milieux Disperses, CNRS UMR 7615, ESPCI, 10 rue Vauquelin, F-75231 Paris Cedex 05 (France)], E-mail: drazen@lpthe.jussieu.fr

    2008-12-10

    Tannin-tannin and tannin-protein interactions in water-ethanol solvent mixtures are studied in the context of red wine tasting. While tannin self-aggregation is relevant for the visual aspect of wine tasting (limpidity and related colloidal phenomena), tannin affinities for salivary proline-rich proteins is fundamental for a wide spectrum of organoleptic properties related to astringency. Tannin-tannin interactions are analyzed in water-ethanol wine-like solvents and the precipitation map is constructed for a typical grape tannin. The interaction between tannins and human salivary proline-rich proteins (PRP) are investigated in the framework of the shell model for micellization, known for describing tannin-induced aggregation of {beta}-casein. Tannin-assisted micellization and compaction of proteins observed by SAXS are described quantitatively and discussed in the case of astringency.

  3. Colloidal Stability & Conformational Changes in β-Lactoglobulin: Unfolding to Self-Assembly

    Directory of Open Access Journals (Sweden)

    Steven Blake

    2015-08-01

    Full Text Available A detailed understanding of the mechanism of unfolding, aggregation, and associated rheological changes is developed in this study for β-Lactoglobulin at different pH values through concomitant measurements utilizing dynamic light scattering (DLS, optical microrheology, Raman spectroscopy, and differential scanning calorimetry (DSC. The diffusion interaction parameter kD emerges as an accurate predictor of colloidal stability for this protein consistent with observed aggregation trends and rheology. Drastic aggregation and gelation were observed at pH 5.5. Under this condition, the protein’s secondary and tertiary structures changed simultaneously. At higher pH (7.0 and 8.5, oligomerizaton with no gel formation occurred. For these solutions, tertiary structure and secondary structure transitions were sequential. The low frequency Raman data, which is a good indicator of hydrogen bonding and structuring in water, has been shown to exhibit a strong correlation with the rheological evolution with temperature. This study has, for the first time, demonstrated that this low frequency Raman data, in conjunction with the DSC endotherm, can be been utilized to deconvolve protein unfolding and aggregation/gelation. These findings can have important implications for the development of protein-based biotherapeutics, where the formulation viscosity, aggregation, and stability strongly affects efficacy or in foods where protein structuring is critical for functional and sensory performance.

  4. Influence of lysolecithin and Tween 80 on the colloidal stability of branched chain amino acids in a nanosuspension system.

    Science.gov (United States)

    Hong, Chi Rac; Lee, Gyu Whan; Paik, Hyun-Dong; Chang, Pahn-Shick; Choi, Seung Jun

    2017-04-15

    This study examined the influence of stabilizers on the solubility and colloidal stability of branched chain amino acids (BCAAs) nanosuspended through high pressure homogenization at 70°C. Although homogenization increased the initial BCAA solubility, irrespective of pH (pH 3 or 6), homogenization alone was not sufficient to increase their long-term solubility. The incorporation of stabilizers into nanosuspensions increased the saturation concentration of BCAAs but the effect of stabilizers on the increase in the saturation concentration of BCAAs was more pronounced at pH 6.0. At pH 6, Tween 80 dramatically increased the colloidal stability of the BCAA nanosuspensions, independent of the BCAA:stabilizer ratio but not at pH 3. However, the effect of lysolecithin on the colloidal stability of nanosuspended BCAAs varied depending on pH and BCAA:lysolecithin ratio. In lysolecithin-related nanosuspensions, there was no clear relationship between the colloidal stability and nanosuspension conditions including pH and BCAA:lysolecithin ratio. This study could provide a useful information on stabilizer selection for the development of liquid or colloidal products with improved solubility and colloidal stability of nanosuspended BCAAs.

  5. PREPARATION OF POLYMER MICROSPHERES WITH PYRIDYL GROUP AND THEIR STABILIZED GOLD METALLIC COLLOIDS

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Narrow disperse poly(ethyleneglycol dimethacrylate-co-4-vinylpyridine) (poly(EGDMA-co-4-VPy)) microspheres were prepared by distillation-precipitation copolymerization of ethyleneglycol dimethacrylate (EGDMA) and 4-vinylpyridine (4-VPy) with 2,2'-azobisisobutyronitrile (AIBN) as initiator in neat acetonitrile. The polymer microspheres containing pyridyl group were then utilized as stabilizer for gold metallic colloids with the diameter around 7 nm, which were prepared by the in situ reduction of gold chloride trihydrate with sodium borohydride through the coordination of the pyridyl group on the gel layer and surface of the microsphere with the gold metallic nano-particles. The catalytic properties of the pyridyl-functionalized microsphere-stabilized gold metallic colloids and the behavior of the stabilized-catalyst for the recycling were investigated with reduction of 4-nitrophenol to 4-aminophenol as a model reaction.

  6. UV and visible light active aqueous titanium dioxide colloids stabilized by surfactants.

    Science.gov (United States)

    Pacia, Michał; Warszyński, Piotr; Macyk, Wojciech

    2014-09-07

    Attempts to increase the stability of photocatalytically active nanodispersions of titanium dioxide over a wide range of pH (3-10) were undertaken. Polyethylene glycols (PEGs) with different molecular weights and polyoxyethylenesorbitan monooleate (Tween® 80) were tested as stabilizing agents of TiO2 nanoparticles. The results of DLS measurements proved the stabilizing effect of Tween® 80 while the systems involving PEGs, independently of the polymer concentration, showed a tendency to form aggregates in neutral solutions. The colloids stabilized with Tween® 80 were photosensitized with 2,3-naphthalenediol (nd) or 2-hydroxy-3-naphthoic acid (hn) or catechol (cat). The photocatalytic activity of such colloids has been assessed in an azure B degradation reaction using both UV and visible light. The nd@TiO2 + Tween colloid appeared particularly photoactive upon visible light irradiation. Moreover, the comparison of activities of nd@TiO2 + Tween and TiO2 + Tween revealed a significantly better performance of the former nanodispersion, independently of the irradiation conditions (UV or visible light). This effect has been explained by different structures of micelles formed in the case of TiO2 and nd@TiO2 stabilized with Tween® 80.

  7. Tunneling mechanism and contact mechanics of colloidal nanoparticle assemblies

    Science.gov (United States)

    Biaye, Moussa; Zbydniewska, Ewa; Mélin, Thierry; Deresmes, Dominique; Copie, Guillaume; Cleri, Fabrizio; Sangeetha, Neralagatta; Decorde, Nicolas; Viallet, Benoit; Grisolia, Jérémie; Ressier, Laurence; Diesinger, Heinrich

    2016-11-01

    Nanoparticle assemblies with thiol-terminated alkyl chains are studied by conducting atomic force microscopy (c-AFM) regarding their use as strain gauges for touch-sensitive panels. Current-force spectroscopy is used as a characterization tool complementary to the macroscopic setup since it allows a bias to be applied to a limited number of junctions, overcoming the Coulomb blockade energy and focusing on the contact electromechanics and the transport mechanism across the ligand. First, transition voltage spectroscopy is applied with varying force to target the underlying tunneling mechanism by observing whether the transition between the ohmic and exponential current-voltage behavior is force-dependent. Secondly, current-force spectroscopy in the ohmic range below the transition voltage is performed. The current-force behavior of the AFM probe in contact with a nanoparticle multilayer is associated with the spread of force and current within the nanoparticle lattice and at the level of adjacent particles by detailed contact mechanics treatment. The result is twofold: concerning the architecture of sensors, this work is a sample case of contact electromechanics at scales ranging from the device scale down to the individual ligand molecule. Regarding transport across the molecule, the vacuum tunneling mechanism is favored over the conduction by coherent molecular states, which is a decision-making aid for the choice of ligand in applications.

  8. Colloidal stability of iron oxide nanocrystals coated with a PEG-based tetra-catechol surfactant

    Science.gov (United States)

    Mondini, Sara; Drago, Carmelo; Ferretti, Anna M.; Puglisi, Alessandra; Ponti, Alessandro

    2013-03-01

    Long-term colloidal stability of magnetic iron oxide nanoparticles (NPs) is an important goal that has not yet been fully achieved. To make an advance in our understanding of the colloidal stability of iron oxide NPs in aqueous media, we prepared NPs comprising a monodisperse (13 nm) iron oxide core coated with a PEG-based (PEG: polyethyleneglycol) surfactant. This consists of a methoxy-terminated PEG chain (MW = 5000 Da) bearing four catechol groups via a diethylenetriamine linker. The surfactant was grafted onto the nanocrystals by ligand exchange monitored by infrared spectroscopy. The colloidal stability of these nanoparticles was probed by monitoring the time evolution of the Z-average intensity-weighted radius Rh and volume-weighted size distribution Pv obtained from analysis of dynamic light scattering data. The nanoparticles showed no sign of aggregation for four months in deionized water at room temperature and also when subjected to thermal cycling between 25 and 75 °C. In 0.01 M PBS (phosphate buffered saline), aggregation (if any) is slow and partial; after 66 h, about 50% of NPs have not aggregated. Aggregation is more effective in 0.15 M NH4AcO buffer, where isolated particles are not observed after 66 h, and especially in acidic NH4AcO/AcOH buffer, where aggregation is complete within 1 h and precipitation is observed. The differing stability of the NPs in the above aqueous media is closely related to their ζ potential.

  9. Quantitative characterization of the colloidal stability of metallic nanoparticles using UV-vis absorbance spectroscopy.

    Science.gov (United States)

    Ray, Tyler R; Lettiere, Bethany; de Rutte, Joseph; Pennathur, Sumita

    2015-03-31

    Plasmonic nanoparticles are used in a wide variety of applications over a broad array of fields including medicine, energy, and environmental chemistry. The continued successful development of this material class requires the accurate characterization of nanoparticle stability for a variety of solution-based conditions. Although many characterization methods exists, there is an absence of a unified, quantitative means for assessing the colloidal stability of plasmonic nanoparticles. We present the particle instability parameter (PIP) as a robust, quantitative, and generalizable characterization technique based on UV-vis absorbance spectroscopy to characterize colloidal instability. We validate PIP performance with both traditional and alternative characterization methods by measuring gold nanorod instability in response to different salt (NaCl) concentrations. We further measure gold nanorod stability as a function of solution pH, salt, and buffer (type and concentration), nanoparticle concentration, and concentration of free surfactant. Finally, these results are contextualized within the literature on gold nanorod stability to establish a standardized methodology for colloidal instability assessment.

  10. Colloidal stability influenced by inhomogeneous surfactant assemblies in confined spaces

    NARCIS (Netherlands)

    Jodar-Reyes, A.B.; Leermakers, F.A.M.

    2009-01-01

    Recently, a molecular-level self-consistent field approach was used to show that some surfactants assemblies (with local cylindrical structure) can bridge between two surfaces that in turn are covered by surfactant bilayers. The stability of such a connection is related to a higher end-cap (free) en

  11. Copolymer adsorption and the effect on colloidal stability.

    NARCIS (Netherlands)

    Bijsterbosch, H.D.

    1998-01-01

    The main aim of the work described in this thesis is to study the effect of different types of copolymers on the stability of aqueous oxide dispersions. Such dispersions are a major component in water-borne paints. In order to obtain a better insight in steric stabilisation we first investigated the

  12. Interactions between laponite and microbial biofilms in porous media: implications for colloid transport and biofilm stability.

    Science.gov (United States)

    Leon-Morales, C Felipe; Leis, Andrew P; Strathmann, Martin; Flemming, Hans-Curt

    2004-09-01

    Quartz sand columns and sand-filled microscope flow cells were used to investigate the transport characteristics of the clay colloid laponite, and a biofilm-forming bacterium, Pseudomonas aeruginosa SG81. Separate experiments were performed with each particle to determine their individual transport characteristics in clean sand columns. In a second set of experiments, bacterial biofilms were formed prior to introduction of the clay colloids. In the independent transport experiments, bacteria and laponite each conformed to known physicochemical principles. A sodium chloride concentration of 7 x 10(-2) M caused complete retention of the laponite within the sand columns. P. aeruginosa SG81 was generally less influenced by ionic strength effects; it showed relatively low mobility at all ionic strengths tested and some (albeit reduced) mobility when introduced to the columns in 1M NaCl, the highest concentration tested, but nevertheless showed reproducible trends. Under conditions favourable to laponite retention and biofilm stability (7 x 10(-2) MNaCl), laponite suspensions were able to remobilise a portion of the attached bacterial biomass. At low ionic strength, the profile of laponite elution was also altered in the presence of a P. aeruginosa biofilm. These observations suggest that while a reduction in ionic strength has a dominant influence on the mobilisation of biological and inorganic colloids, the presence of laponite and biomass can have a distinct influence on the mobility of both types of colloids. Since these events are likely to occur in subsurface environments, our results suggest that colloid-biofilm interactions will have implications for colloid-bound contaminant transport and the remobilisation of pathogens.

  13. The study of the antimicrobial activity of colloidal solutions of silver nanoparticles prepared using food stabilizers.

    Science.gov (United States)

    Balandin, G V; Suvorov, O A; Shaburova, L N; Podkopaev, D O; Frolova, Yu V; Ermolaeva, G A

    2015-06-01

    The bactericidal effect of colloidal solutions of silver nanoparticles based on food stabilizers, gum arabic and chitosan, against bacterial cultures of microorganisms in food production is described. The antibacterial activity of nanotechnology products containing different amounts of stabilizing additives when applied to solid pH-neutral substrates is studied. For its evaluation a method making it possible to take into account the capability of nanoparticles to diffuse in solid media was applied. Minimal inhibitory concentrations of nanoparticles used against Erwinia herbicola, Pseudomonas fluorescens, Bacillus subtilis, Sarcina flava were found. A suggestion was made concerning the influence of the spatial structure of bacteria on the antibacterial activity of colloidal solutions of silver nanoparticles. The data concerning the antibacterial activity and minimal inhibiting concentrations of nanoparticles may be used for development of products suppressing activity of microorganisms hazardous for food production.

  14. Coadsorption of IgG and BSA onto sulfonated polystyrene latex: II. Colloidal stability and immunoreactivity.

    Science.gov (United States)

    Peula, J M; Hidalgo-Alvarez, R; de las Nieves, F J

    1995-01-01

    The present work deals with the study of the colloidal stability and immunoreactivity of sulfonated polystyrene latex particles covered by different amounts of m-BSA and IgG/a-CRP. These proteins have been previously adsorbed onto a sulfonated latex by sequential and competitive coadsorption experiments and it was possible to obtain latex-protein particles with different degrees of coverage by each protein. The latex particles, fully or partially covered by each protein (termed latex-protein complexes), were resuspended under several conditions (different pH and ionic strength values) and their colloidal stability, vs the addition of the electrolyte was studied using turbidity measurements. This stability appeared at a high degree of coverage by BSA and at a pH in which the BSA was negatively charged. At a high degree of coverage by IgG, the latex particles were unstable at all pHs. As a final part of this work, the immunoreactivity of several complexes was studied following the changes in the turbidity after the addition of CRP antigen. Only the complexes which were colloidally stable gave detectable reactivity. However, the complexes with a relatively low degree of coverage by IgG/a-CRP gave good immunoreactivity. Therefore, the latex-protein complex properties depended on the percentage of BSA or IgG adsorbed and on the electric state of the proteins at the redispersion pH. Under specific incubation conditions, sulfonated latex covered by significant IgG/BSA percentages was obtained, which showed a high colloidal stability and good immunoreactivity.

  15. Phase equilibria in stratified thin liquid films stabilized by colloidal particles

    OpenAIRE

    Blawzdziewicz, J.; Wajnryb, E.

    2005-01-01

    Phase equilibria between regions of different thickness in thin liquid films stabilized by colloidal particles are investigated using a quasi-two-dimensional thermodynamic formalism. Appropriate equilibrium conditions for the film tension, normal pressure, and chemical potential of the particles in the film are formulated, and it is shown that the relaxation of these parameters occurs consecutively on three distinct time scales. Film stratification is described quantitatively for a hard-spher...

  16. SYNTHESIS OF POLYMER-STABILIZED PLATINUM/RUTHENIUM BIMETALLIC COLLOIDS AND THEIR CATALYTIC PROPERTIES FOR SELECTIVE HYDROGENATION OF CROTONALDEHYDE

    Institute of Scientific and Technical Information of China (English)

    Wei-xia Tu; Han-fan Liu

    2005-01-01

    Polymer-stabilized platinum/ruthenium bimetallic colloids (Pt/Ru) were synthesized by polyol reduction with microwave irradiation and characterized by TEM and XPS. The colloidal nanoparticles have small and narrow size distributions. Catalytic performance of the Pt/Ru colloidal catalysts was investigated on the selective hydrogenation of crontonaldehyde (CRAL). A suitable amount of the added metal ions and base can improve the selectivity of CRAL to crotylalcohol (CROL) remarkably. The catalytic activity and the selectivity are dependent on the compositions of bimetallic colloids. Thereinto, PVP-stabilized 9Pt/1Ru colloid with a molar ratio of metals Pt:Ru = 9:1 shows the highest catalytic selectivity 77.3% to CROL at 333 K under 4.0 MPa of hydrogen.

  17. Effect of Grape Seed Proanthocyanidin-Gelatin Colloidal Complexes on Stability and in Vitro Digestion of Fish Oil Emulsions.

    Science.gov (United States)

    Su, Yu-Ru; Tsai, Yi-Chin; Hsu, Chun-Hua; Chao, An-Chong; Lin, Cheng-Wei; Tsai, Min-Lang; Mi, Fwu-Long

    2015-11-25

    The colloidal complexes composed of grape seed proanthocyanidin (GSP) and gelatin (GLT), as natural antioxidants to improve stability and inhibit lipid oxidation in menhaden fish oil emulsions, were evaluated. The interactions between GSP and GLT, and the chemical structures of GSP/GLT self-assembled colloidal complexes, were characterized by isothermal titration calorimetry (ITC), circular dichroism (CD), and Fourier transform infrared spectroscopic (FTIR) studies. Fish oil was emulsified with GLT to obtain an oil-in-water (o/w) emulsion. After formation of the emulsion, GLT was fixed by GSP to obtain the GSP/GLT colloidal complexes stabilized fish oil emulsion. Menhaden oil emulsified by GSP/GLT(0.4 wt %) colloidal complexes yielded an emulsion with smaller particles and higher emulsion stability as compared to its GLT emulsified counterpart. The GSP/GLT colloidal complexes inhibited the lipid oxidation in fish oil emulsions more effectively than free GLT because the emulsified fish oil was surrounded by the antioxidant GSP/GLT colloidal complexes. The digestion rate of the fish oil emulsified with the GSP/GLT colloidal complexes was reduced as compared to that emulsified with free GLT. The extent of free fatty acids released from the GSP/GLT complexes stabilized fish oil emulsions was 63.3% under simulated digestion condition, indicating that the fish oil emulsion was considerably hydrolyzed with lipase.

  18. Investigation on the Stability of Aluminosilicate Colloids by Various Analytical Tools

    Energy Technology Data Exchange (ETDEWEB)

    Putri, Kirana Y.; Lee, D. H.; Yun, J. I. [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2010-05-15

    Colloids are ubiquitous in natural aquatic systems. Aquatic colloids may play a significant carrier role for radionuclide migration in aquifer systems. Being omnipresent in natural aquatic systems, aluminosilicate colloids are considered as a kernel for various aquatic colloids. Characterization of aluminosilicate colloids formed under various geochemical conditions is of importance to understand their chemical behavior in natural aquatic systems. In this work, a preliminary study on the formation of aluminosilicate colloids with a help of colorimetry and other colloid detection techniques is presented

  19. Surface functionalized LSMO nanoparticles with improved colloidal stability for hyperthermia applications

    Science.gov (United States)

    Thorat, N. D.; Khot, V. M.; Salunkhe, A. B.; Prasad, A. I.; Ningthoujam, R. S.; Pawar, S. H.

    2013-03-01

    LSMO (La0.7Sr0.3MnO3) magnetic nanoparticles (MNPs) coated with double layer oleic acid (OA) surfactant are prepared to make a water based magnetic nanofluid for hyperthermia application. Various experimental techniques are used for bilayer coating analysis. The effect of the bilayer coating on magnetic properties is studied by superconducting quantum interface device (SQUID). Colloidal behaviour of coated MNPs in aqueous medium is studied by the zeta potential and dynamic light scattering. The effects of pH and ionic strength on the colloidal stability of the MNPs are studied in detail. For the bilayer-coated LSMO MNPs aggregation is not observed even in high ionic strength and at physiological pH (7.4). For making the nanofluid of the bilayer-coated MNPs the colloidal stability is studied in physiological media like phosphate buffer solution. Under induction heating experiment, hyperthermia temperature (42-43 °C) could be achieved by the bilayer-coated sample at a magnetic field of 168-335 Oe and frequency of 267 kHz. The bilayer OA coating can hinder the agglomeration of MNPs significantly and produce stable suspension with improved hyperthermia properties. The bilayer OA coating also improves the specific absorption rate (SAR) of LSMO MNPs from 25 to 40 W g-1.

  20. Stabilization through precipitation in a system of colloidal iron(III) pyrophosphate salts.

    Science.gov (United States)

    van Leeuwen, Y Mikal; Velikov, Krassimir P; Kegel, Willem K

    2012-09-01

    The ionic strength of a solution decreases during the precipitation of an insoluble salt, which can cause an initially unstable colloidal system to stabilize during its formation. We show this effect in the precipitation and aging of colloidal iron(III) pyrophosphate, where we observe two distinct stages in the aggregation process. The first stage is the formation of nanoparticles that immediately aggregate into clusters with sizes on the order of 200 nm. In the second stage these clusters slowly grow in size but remain in dispersion for days, even months for dialyzed systems. Eventually these clusters become macroscopically large and sediment out of dispersion. Noting the clear instability of the nanoparticles, it is interesting to find two stages in their aggregation even without the use of additives such as surface active molecules. This is explained by accounting for the rapid decrease of ionic strength during precipitation, rendering the nanoparticles relatively stable when precipitation is complete. Calculating the interaction potentials for this scenario we find good agreement with the experimental observations. These results indicate that coupling of ionic strength to aggregation state can be significant and should be taken into account when considering colloidal stability of insoluble salts.

  1. Mechanics and stability of vesicles and droplets in confined spaces

    Science.gov (United States)

    Benet, Eduard; Vernerey, Franck J.

    2016-12-01

    The permeation and trapping of soft colloidal particles in the confined space of porous media are of critical importance in cell migration studies, design of drug delivery vehicles, and colloid separation devices. Our current understanding of these processes is however limited by the lack of quantitative models that can relate how the elasticity, size, and adhesion properties of the vesicle-pore complex affect colloid transport. We address this shortcoming by introducing a semianalytical model that predicts the equilibrium shapes of a soft vesicle driven by pressure in a narrow pore. Using this approach, the problem is recast in terms of pressure and energy diagrams that characterize the vesicle stability and permeation pressures in different conditions. We particularly show that the critical permeation pressure for a vesicle arises from a compromise between the critical entry pressure and exit pressure, both of which are sensitive to geometrical features, mechanics, and adhesion. We further find that these results can be leveraged to rationally design microfluidic devices and diodes that can help characterize, select, and separate colloids based on physical properties.

  2. Statistical mechanics of a colloidal suspension in contact with a fluctuating membrane.

    Science.gov (United States)

    Bickel, T; Benhamou, M; Kaïdi, H

    2004-11-01

    Surface effects are generally prevailing in confined colloidal systems. Here we report on dispersed nanoparticles close to a fluid membrane. Exact results regarding the static organization are derived for a dilute solution of nonadhesive colloids. It is shown that thermal fluctuations of the membrane broaden the density profile, but on average colloids are neither accumulated nor depleted near the surface. The radial correlation function is also evaluated, from which we obtain the effective pair potential between colloids. This entropically driven interaction shares many similarities with the familiar depletion interaction. It is shown to be always attractive with range controlled by the membrane correlation length. The depth of the potential well is comparable to the thermal energy, but depends only indirectly upon membrane rigidity. Consequences for the stability of the suspension are also discussed.

  3. Stability of colloidal silver nanoparticles trapped in lipid bilayer: effect of lecithin concentration and applied temperature.

    Science.gov (United States)

    Barani, Hossein; Montazer, Majid; Braun, Hans-Georg; Dutschk, Victoria

    2014-12-01

    The use of silver nanoparticle on various substrates has been widespread because of its good antibacterial properties that directly depend on the stability of the silver nanoparticles in a colloidal suspension. In this study, the colloidal solutions of the silver nanoparticles were synthesised by a simple and safe method by using lecithin as a stabilising agent and their stability was examined at various temperatures. The effect of the lecithin concentrations on the stability of the synthesised silver nanoparticles was examined from 25 to 80°C at 5°C intervals, by recording the changes in the UV-vis absorption spectra, the hydrodynamic diameter and the light scattering intensity of the silver nanoparticles. In addition, the morphology of the synthesised silver nanoparticles was investigated with the low-voltage scanning electron microscopy and transmission electron microscopy. The results indicated that increasing temperature caused different changes in the size of the stabilised and the unstabilised silver nanoparticles. The size of the stabilised silver nanoparticles reduced from 38 to 36 nm during increasing temperature, which confirmed good stability.

  4. Amphiphilic comblike polymers enhance the colloidal stability of Fe(3)O(4) nanoparticles.

    Science.gov (United States)

    Kim, Myeongjin; Jung, Jaeyeon; Lee, Jonghwan; Na, Kyunga; Park, Subeom; Hyun, Jinho

    2010-03-01

    Stable colloidal dispersions of magnetite (Fe(3)O(4)) nanoparticles (MNPs) were obtained with the inclusion of an amphiphilic comblike polyethylene glycol derivative (CL-PEG) as an amphiphilic polymeric surfactant. Both the size and morphology of the resulting CL-PEG-modified MNPs could be controlled and were characterized by transmission electron microscopy (TEM). The interaction between MNPs and CL-PEG was confirmed by the presence of characteristic infrared absorption peaks, and the colloidal stability of the nanoparticle dispersion in water was evaluated by long-term observation of the dispersion using UV-visible spectroscopy. SQUID measurements confirmed the magnetization of CL-PEG-modified MNPs. The zeta potential of the CL-PEG-modified MNPs showed a dramatic conversion from positive to negative in response to the pH of the surrounding aqueous medium due to the presence of carboxyl groups at the surface. These carboxyl groups can be used to functionalize the MNPs with biomolecules for biotechnological applications. However, regardless of surface electrostatics, the flexible, hydrophilic side chains of CL-PEG-modified MNPs prevented the approach of adjacent nanoparticles, thereby resisting aggregation and resulting in a stable aqueous colloid. The cytotoxicity of MNPs and CL-PEG-modified MNPs was evaluated by a MTT assay.

  5. Effect of polyethylene glycol conjugation on conformational and colloidal stability of a monoclonal antibody antigen-binding fragment (Fab').

    Science.gov (United States)

    Roque, Cristopher; Sheung, Anthony; Rahman, Nausheen; Ausar, S Fernando

    2015-02-01

    We have investigated the effects of site specific "hinge" polyethylene glycol conjugation (PEGylation) on thermal, pH, and colloidal stability of a monoclonal antibody antigen-binding fragment (Fab') using a variety of biophysical techniques. The results obtained by circular dichroism (CD), ultraviolet (UV) absorbance, and fluorescence spectroscopy suggested that the physical stability of the Fab' is maximized at pH 6-7 with no apparent differences due to PEGylation. Temperature-induced aggregation experiments revealed that PEGylation was able to increase the transition temperature, as well as prevent the formation of visible and subvisible aggregates. Statistical comparison of the three-index empirical phase diagram (EPD) revealed significant differences in thermal and pH stability signatures between Fab' and PEG-Fab'. Upon mechanical stress, micro-flow imaging (MFI) and measurement of the optical density at 360 nm showed that the PEG-Fab' had significantly higher resistance to surface-induced aggregation compared to the Fab'. Analysis of the interaction parameter, kD, indicated repulsive intermolecular forces for PEG-Fab' and attractive forces for Fab'. In conclusion, PEGylation appears to protect Fab' against thermal and mechanical stress-induced aggregation, likely due to a steric hindrance mechanism.

  6. Effect of electrolytes on colloidal stability and swelling of hydroxypropyl cellulose microgels

    Science.gov (United States)

    Mithra, K.; Khandai, Santripti; Jena, Sidhartha S.

    2016-05-01

    Hydroxypropyl Cellulose (HPC) microgels were prepared by emulsion polymerization method. The volume phase transition temperature (VPTT) and swelling properties were investigated using Dynamic Light Scattering (DLS). The VPTT for the HPC microgels was found to be˜44°C. Microgel particles swelled˜'3' times of their original size on decreasing temperature from 50°C to 25 °C. In addition we have also studied the effect of salts, sodium nitrate and sodium bromide in the Hofmeister series on deswelling and colloidal stability of HPC microgels using DLS and turbidity measurements respectively. M icrogel particles swelled in presence of NaN03 when its concentration was increased from 10-4 to 0.5 M and deswelled beyond it. As oppose to this, swelling of microgels in presence of NaBr was seen only upto 10-3 M and beyond which deswelling of microgels was observed. The results obtained are consistent with Hofmeister series of anions. Turbidity results showed that the colloidal stability of HPC microgel dispersion was dependent on ionic strength and type of added salt. For both salts, stability of microgels was found to decrease with rise in salt concentration.

  7. Influence of the initial state of carbon nanotubes on their colloidal stability under natural conditions

    Energy Technology Data Exchange (ETDEWEB)

    Schwyzer, Irene [Empa - Swiss Federal Laboratories for Materials Science and Technology, CH-9014 St. Gallen (Switzerland); Eawag - Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Duebendorf (Switzerland); Kaegi, Ralf; Sigg, Laura [Eawag - Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Duebendorf (Switzerland); Magrez, Arnaud [EPFL - Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne (Switzerland); Nowack, Bernd, E-mail: nowack@empa.ch [Empa - Swiss Federal Laboratories for Materials Science and Technology, CH-9014 St. Gallen (Switzerland)

    2011-06-15

    The colloidal stability of dry and suspended carbon nanotubes (CNTs) in the presence of amphiphilic compounds (i.e. natural organic matter or surfactants) at environmentally realistic concentrations was investigated over several days. The suspensions were analyzed for CNT concentration (UV-vis spectroscopy), particle size (nanoparticle tracking analysis), and CNT length and dispersion quality (TEM). When added in dry form, around 1% of the added CNTs remained suspended. Pre-dispersion in organic solvent or anionic detergent stabilized up to 65% of the added CNTs after 20 days of mild shaking and 5 days of settling. The initial state of the CNTs (dry vs. suspended) and the medium composition hence are critical determinants for the partitioning of CNTs between sediment and the water column. TEM analysis revealed that single suspended CNTs were present in all suspensions and that shaking and settling resulted in a fractionation of the CNTs with shorter CNTs remaining predominantly in suspension. - Highlights: > Individually suspended CNTs are present under environment relevant conditions. > The number of suspended CNTs varies depending on the medium composition. > Surfactants at environmental concentrations have no suspending effect on dry CNTs. > Pre-dispersed CNTs are more stable in suspension than dry CNTs. - The colloidal stability of CNTs varies a lot depending on the initial state of the CNTs (dry vs. pre-dispersed), the applied dispersant for pre-suspension, and the composition of the medium.

  8. PEGylation of SPIONs by polycondensation reactions: a new strategy to improve colloidal stability in biological media

    Energy Technology Data Exchange (ETDEWEB)

    Viali, Wesley Renato; Silva Nunes, Eloiza da; Santos, Caio Carvalho dos [Universidade Estadual Paulista, Laboratorio de Materiais Magneticos e Coloides, Departamento de Fisico-quimica, Instituto de Quimica (Brazil); Silva, Sebastiao William da; Aragon, Fermin Herrera; Coaquira, Jose Antonio Huamani; Morais, Paulo Cesar [Universidade de Brasilia, Instituto de Fisica, Nucleo de Fisica Aplicada (Brazil); Jafelicci, Miguel, E-mail: jafeli@iq.unesp.br [Universidade Estadual Paulista, Laboratorio de Materiais Magneticos e Coloides, Departamento de Fisico-quimica, Instituto de Quimica (Brazil)

    2013-08-15

    In this study, we report on a new route of PEGylation of superparamagnetic iron oxide nanoparticles (SPIONs) by polycondensation reaction with carboxylate groups. Structural and magnetic characterizations were performed by X-ray diffractometry (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and vibrating sample magnetometry (VSM). The XRD confirmed the spinel structure with a crystallite average diameter in the range of 3.5-4.1 nm in good agreement with the average diameter obtained by TEM (4.60-4.97 nm). The TGA data indicate the presence of PEG attached onto the SPIONs' surface. The SPIONs were superparamagnetic at room temperature with saturation magnetization (M{sub S}) from 36.7 to 54.1 emu/g. The colloidal stability of citrate- and PEG-coated SPIONs was evaluated by means of dynamic light scattering measurements as a function of pH, ionic strength, and nature of dispersion media (phosphate buffer and cell culture media). Our findings demonstrated that the PEG polymer chain length plays a key role in the coagulation behavior of the Mag-PEG suspensions. The excellent colloidal stability under the extreme conditions we evaluated, such as high ionic strength, pH near the isoelectric point, and cell culture media, revealed that suspensions comprising PEG-coated SPION, with PEG of molecular weight 600 and above, present steric stabilization attributed to the polymer chains attached onto the surface of SPIONs.

  9. Colloidal particles as liquid dispersion stabilizer: Pickering emulsions and materials thereof

    Science.gov (United States)

    Schmitt, Véronique; Destribats, Mathieu; Backov, Rénal

    2014-10-01

    Solid stabilized emulsions, also referred to as Pickering emulsions, are very diverse owing to the large variety of available colloidal particles from naturally occurring to synthesized ones, from hard to very deformable ones and from spheres to more complex shaped particles. Here we illustrate this variety and, despite this huge diversity, we aim at highlighting the common features. We discuss next the remaining open questions that, in our point of view, should sustain special efforts in the future and we illustrate elaboration of original materials based on Pickering emulsions. xml:lang="fr"

  10. Stable colloids in molten inorganic salts.

    Science.gov (United States)

    Zhang, Hao; Dasbiswas, Kinjal; Ludwig, Nicholas B; Han, Gang; Lee, Byeongdu; Vaikuntanathan, Suri; Talapin, Dmitri V

    2017-02-15

    A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other. Electrostatic stabilization of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute-solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute-solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

  11. Stable colloids in molten inorganic salts

    Science.gov (United States)

    Zhang, Hao; Dasbiswas, Kinjal; Ludwig, Nicholas B.; Han, Gang; Lee, Byeongdu; Vaikuntanathan, Suri; Talapin, Dmitri V.

    2017-02-01

    A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other. Electrostatic stabilization of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute–solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute–solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

  12. Depletion induced encapsulation by dumbbell-shaped patchy colloids stabilize microspheres against aggregation.

    Science.gov (United States)

    Wolters, Joost Robert; Verweij, Joanne E; Avvisati, Guido; Dijkstra, Marjolein; Kegel, Willem K

    2017-03-08

    In this paper, we demonstrate the stabilization of polystyrene microspheres by encapsulating them with dumbbell-shaped colloids with a sticky and a non-sticky lobe. Upon adding a depletant, an effective short ranged attraction is induced between the microspheres and the smaller, smooth lobes of the dumbbells, making those specifically sticky, whereas the interaction with the larger lobes of the dumbbells is considerably less attractive due to their rough surface, which reduces the overlap volume and leaves them non-sticky. The encapsulation of the microspheres by these rough-smooth patchy dumbbells is investigated using a combination of experiments and computer simulations, both resulting in partial coverage of the template particles. For larger microspheres, the depletion attraction is stronger, resulting in a larger fraction of dumbbells that are attached with both lobes to the surface of microspheres. We thus find a template curvature dependent orientation of the dumbbells. In the Monte Carlo simulations, the introduction of such a small, curvature dependent attraction between the rough lobes of the dumbbells resulted in an increased coverage. However, kinetic constraints imposed by the dumbbell geometry seem to prevent optimal packing of the dumbbells on the template particles under all investigated conditions in experiments and simulations. Despite the incomplete coverage, the encapsulation by dumbbell particles does prevent aggregation of the microspheres, thus acting as a colloid-sized steric stabilizer.

  13. Facile synthesis and catalytic properties of silver colloidal nanoparticles stabilized by SDBS

    Indian Academy of Sciences (India)

    Wen Wang; Yinmin Song; Quansheng Liu; Keli Yang

    2014-06-01

    A facile method was explored to prepare stable silver colloidal nanoparticles (AgCNPs) in water. Sodium dodecyl benzene sulfonate (SDBS) was used as the stabilizing agent, without addition of any co-surfactant. The reaction was rapid and the product prepared at different conditions was measured by transmission electron microscopy (TEM) and UV-Vis spectroscopy. The results showed that AgCNPs stabilized by SDBS was stable in water with narrow size distribution (1-5 nm). The amount of surfactant has great influence on the products. When the molar ratio of Ag+ to SDBS increased to 1 : 4, AgCNPs can be obtained with high dispersion (2-3 nm), which has high catalytic activity on reduction of 4-nitrobenzoic acid to 4-aminobenzoic acid.

  14. Mechanism of action and clinical benefits of colloidal oatmeal for dermatologic practice.

    Science.gov (United States)

    Cerio, Rino; Dohil, Magdalene; Jeanine, Downie; Magina, Sofia; Mahé, Emmanuel; Stratigos, Alexander J

    2010-09-01

    Colloidal oatmeal has a long history of beneficial use in dermatology. It is a natural product that has an excellent safety record and has demonstrated efficacy for the treatment of atopic dermatitis, psoriasis, drug-induced rash and other conditions. In recent years, in vitro and in vivo studies have begun to elucidate the multiple mechanisms of action of naturally derived colloidal oatmeal. Evidence now describes its molecular mechanisms of anti-inflammatory and antihistaminic activity. The avenanthramides, a recently described component of whole oat grain, are responsible for many of these effects. Studies have demonstrated that avenanthramides can inhibit the activity of nuclear factor kappaB and the release of proinflammatory cytokines and histamine, well known key mechanisms in the pathophysiology of inflammatory dermatoses. Topical formulations of natural colloidal oatmeal should be considered an important component of therapy for atopic dermatitis and other conditions and may allow for reduced use of corticosteroids and calcineurin inhibitors.

  15. Superparamagnetic iron oxide/chitosan core/shells for hyperthermia application: Improved colloidal stability and biocompatibility

    Energy Technology Data Exchange (ETDEWEB)

    Patil, R.M.; Shete, P.B.; Thorat, N.D.; Otari, S.V. [Center for Interdisciplinary Research, D.Y. Patil University, Kolhapur 416006, MS (India); Barick, K.C.; Prasad, A.; Ningthoujam, R.S. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, MS (India); Tiwale, B.M. [Center for Interdisciplinary Research, D.Y. Patil University, Kolhapur 416006, MS (India); Pawar, S.H., E-mail: pawar_s_h@yahoo.com [Center for Interdisciplinary Research, D.Y. Patil University, Kolhapur 416006, MS (India)

    2014-04-15

    Superparamagnetic magnetite nanoparticles are of great interest due to their potential biomedical applications. In the present investigation, Fe{sub 3}O{sub 4} magnetic nanoparticles were prepared by alkaline precipitation using ferrous chloride as the sole source. An amphiphilic polyelectrolyte with the property of biocompatibility and functional carboxyl groups was used as a stabilizer to prepare a well-dispersed suspension of superparamagnetic Fe{sub 3}O{sub 4} nanoparticles. The final material composed of Fe{sub 3}O{sub 4} core and chitosan (CH) shell was produced. The amino groups of CH coated on Fe{sub 3}O{sub 4} nanoparticles were further cross linked using glutaraldehyde (GLD) for stable coating. FTIR spectra, XPS and TGA confirmed the coating of CH/GLD on the surface of Fe{sub 3}O{sub 4} nanoparticles. XRD patterns indicate the pure phase Fe{sub 3}O{sub 4} with a spinel structure. The nanoparticles were superparamagnetic at room temperature with saturation magnetization values for bare and coated nanoparticles which were 51.68 emu/g and 48.60 emu/g, respectively. Zeta potential values showed higher colloidal stability of coated nanoparticles than the bare one. Cytotoxicity study up to 2 mg mL{sup −1} concentration showed no drastic change in cell viability of nanoparticles after coating. Also, coated nanoparticles showed increased SAR value, making them suitable for hyperthermia therapy application. - Highlights: • Fe{sub 3}O{sub 4} nanoparticles were synthesized from FeCl{sub 2} as the sole source by alkaline precipitation. • Coating of Fe{sub 3}O{sub 4} nanoparticles was done with chitosan by simple ultrasonication. • Chitosan cross-linked with glutaraldehyde. • High colloidal stability was observed. • Increased SAR value and least cytotoxicity were observed.

  16. The Colloidal Stabilization of Quantum Dots: Towards Manufacturable, Efficient Solution-Processed Solar Cells

    Science.gov (United States)

    Rollny, Lisa

    Understanding colloidal stabilization can influence the design of optoelectronic devices and enable improvements to their performance and stability. For photovoltaics, important characteristics of the active layer material are high conductivity along with a minimum of recombination centers. In order to capitalize on the benefits of solution-processed materials, it is important to minimize the number of processing steps: ideally, to achieve a low-cost solution, materials would be deposited using a single process step compatible with roll-to-roll manufacturing. Prior to this work, the highest-performing colloidal quantum dots (CQD) solar cells have relied on several deposition steps that are repeated in a layer-by-layer (LBL) fashion. The purpose of these process steps has been to remove the long insulating ligands used in synthesis and replace them with short ligands that allow electrical conduction. The large number of steps combined, typically implemented via spin coating, leads to inefficient materials utilization and fails to show a path to a manufacturable solution. In this work, the first CQD solar cells were designed, built, and characterized combining state-of-art performance with scalable manufacture. Firstly, I report the first automated CQD synthesis to result in CQDs that form high-performance CQD solar cells. I analyze the CQD synthesis and by separating it into two phases---nucleation and growth phase---my insights are used to create higher-quality CQDs exhibiting enhanced monodispersity. I then proceed to develop a CQD ink: a CQD solution ready for direct deposition to form a semiconducting film exhibiting low trap state density. In early trials the CQD ink showed only limited power conversion efficiencies of 2%. I designed a new ink strategy, which I term cleavable hemiketal ligands. This novel two-component ligand strategy enables the combination of colloidal stabilization (via this longer two-component ligand) and cleavability (enabling excellent

  17. Stabilization of sputtered gold and silver nanoparticles in PEG colloid solutions

    Energy Technology Data Exchange (ETDEWEB)

    Slepička, P., E-mail: petr.slepicka@vscht.cz; Elashnikov, R. [University of Chemistry and Technology Prague, Department of Solid State Engineering (Czech Republic); Ulbrich, P. [University of Chemistry and Technology Prague, Department of Biochemistry and Microbiology (Czech Republic); Staszek, M. [University of Chemistry and Technology Prague, Department of Solid State Engineering (Czech Republic); Kolská, Z. [University of J. E. Purkyně, Faculty of Science (Czech Republic); Švorčík, V. [University of Chemistry and Technology Prague, Department of Solid State Engineering (Czech Republic)

    2015-01-15

    In this study, a simple technique for preparation of colloid solution of metal nanoparticles in polyethylene glycol (PEG)/H{sub 2}O is described. By this technique, stable colloidal metal solutions can be prepared ready for use without application of chemical reactions, stabilizers, or reducing agents. The nanoparticles are created by direct sputtering of metal into PEG. The influence of sputter conditions and the concentration of PEG/H{sub 2}O on the properties of nanoparticles was studied. The nanoparticles were characterized by transmission electron microscopy, atomic absorption spectrometry, dynamic light scattering, and UV–Vis spectroscopy. UV–Vis spectra of gold nanoparticle solution exhibit localized surface plasmon resonance characteristic peaks located in the region 513–560 nm (PEG/H{sub 2}O—1/1), 509–535 nm (PEG/H{sub 2}O—1/9), and for silver nanoparticles in the region from 401 to 421 nm. Silver nanoparticles have a broader size distribution compared with gold ones. An appropriate choice of concentration, mixing, and deposition conditions allows preparing the stable solution of gold or silver nanoparticles.

  18. Colloidal polypyrrole

    Science.gov (United States)

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized aromatic heterocyclic monomer, a stabilizing effective amount of a vinyl pyridine-containing polymer and dopant anions and a method of preparing such polymer compositions are disclosed.

  19. Role of electrostatic repulsion on colloidal stability of Bacillus halmapalus alpha-amylase

    DEFF Research Database (Denmark)

    Olsen, Søren Nymand; Andersen, Kim Bruno; Randolf, Theodor

    2009-01-01

    The colloidal stability of charged particles in suspension is often controlled by electrostatic repulsion, which can be rationalized in a semi-quantitative way by the DLVO theory. In the current study, we investigate this approach towards understanding irreversible protein aggregation, using Baci...

  20. Harnessing the advantages of hard and soft colloids by the use of core-shell particles as interfacial stabilizers

    NARCIS (Netherlands)

    Buchcic, C.; Tromp, R.H.; Meinders, M.B.J.; Cohen Stuart, M.A.

    2017-01-01

    The ability of colloidal particles to penetrate fluid interfaces is a crucial factor in the preparation of particle stabilized disperse systems such as foams and emulsions. For hard micron-sized particles the insertion into fluid interfaces requires substantial energy input, but soft particles

  1. Chemical mechanism of flocculation and deposition of clay colloids in coastal aquifers

    Science.gov (United States)

    Zhou, Jun; Qiu, Lixia; Lin, Guoqing; Yan, Xiaoyun; Chen, Xiaolan; Pang, Honglu

    2016-10-01

    Seawater intrusion has become one of serious environmental problems in coastal areas. During the replacement of saline water by fresh water in the aquifers, in-situ clay could be released, transport and deposit in the porous media due to the change of hydrodynamic and geochemical conditions, which resulted in the increasing of particle size, plugging of pores and reduction of the permeability. Batch experiments and sand column experiments were explored to study the relationships between the flocculation of in-situ clay and geochemical conditions, by changing ionic strength and ionic type of clay suspension. Column outflow was analyzed for suspended particles and electrical conductivity. The total percentage of colloid straining and interception distribution in porous media was calculated. The results indicate that porous media had an effect on the interception of clay colloid particles with about 10 percent clay colloids captured due to the rough surfaces and spatial structure of porous media. Ionic strength played a key role on the permeability reductions. The higher ionic strength is, the greater the amount of colloidal particles trapped. Ionic type also had a significant effect on the interception of clay colloid particles. Ripening was the main mechanism for the interception within porous media when the bulk solution was potassium chloride while blocking happened when the bulk solution was sodium chloride. The distribution of clay colloids in porous media was heterogeneous. The closer to the sand column inlet was the less interception of clay colloids was. The results can provide the scientific basis for preventing the water sensitivity during the process of salty aquifer restoration.

  2. Kinetics and cluster morphology evolution of shear-driven aggregation of well-stabilized colloids.

    Science.gov (United States)

    Meng, Xia; Wu, Hua; Morbidelli, Massimo

    2015-01-27

    We investigate the shear-driven aggregation of polystyrene colloids that are stabilized by both fixed and surfactant charges, using a microchannel device, in various particle volume fractions. The objective is to understand how the primary particles evolve to clusters with shearing time, how the cluster morphology develops along the aggregation with the effect of breakage and restructuring, and whether non-Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions are present, affecting the kinetics. The time evolution of the primary particle conversion to big clusters is characterized by an induction time, followed by an explosive increase when the cluster size reaches a certain critical value, which confirms the self-acceleration kinetics developed in the literature. The size of the critical clusters has been quantified for the first time, and its scaling with the shear rate follows the literature prediction well. Moreover, analysis of the shear-driven kinetics confirms the presence of substantial non-DLVO interactions in the given system.

  3. Solitary waves and their stability in colloidal media: semi-analytical solutions

    CERN Document Server

    Marchant, T R

    2012-01-01

    Spatial solitary waves in colloidal suspensions of spherical dielectric nanoparticles are considered. The interaction of the nanoparticles is modelled as a hard-sphere gas, with the Carnahan-Starling formula used for the gas compressibility. Semi-analytical solutions, for both one and two spatial dimensions, are derived using an averaged Lagrangian and suitable trial functions for the solitary waves. Power versus propagation constant curves and neutral stability curves are obtained for both cases, which illustrate that multiple solution branches occur for both the one and two dimensional geometries. For the one-dimensional case it is found that three solution branches (with a bistable regime) occur, while for the two-dimensional case two solution branches (with a single stable branch) occur in the limit of low background packing fractions. For high background packing fractions the power versus propagation constant curves are monotonic and the solitary waves stable for all parameter values. Comparisons are mad...

  4. Cobalt ferrite nanoparticles with improved aqueous colloidal stability and electrophoretic mobility

    Energy Technology Data Exchange (ETDEWEB)

    Munjal, Sandeep, E-mail: drsandeepmunjal@gmail.com; Khare, Neeraj, E-mail: nkhare@physics.iitd.ernet.in [Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016 (India)

    2016-04-13

    We have synthesized CoFe{sub 2}O{sub 4} (CFO) nanoparticles of size ∼ 12.2 nm by hydrothermal synthesis method. To control the size of these CFO nanoparticles, oleic acid was used as a surfactant. The inverse spinel phase of the synthesized nanoparticles was confirmed by X-ray diffraction method. As synthesized oleic acid coated CFO (OA@CFO) nanoparticles has very less electrophoretic mobility in the water and are not water dispersible. These OA@CFO nanoparticles were successfully turned into water soluble phase with a better colloidal aqueous stability, through a chemical treatment using citric acid. The modified citric acid coated CFO (CA@CFO) nanoparticles were dispersible in water and form a stable aqueous solution with high electrophoretic mobility.

  5. Poly(acrylic acid)-stabilized colloidal gold nanoparticles: synthesis and properties.

    Science.gov (United States)

    Jans, Hilde; Jans, Karolien; Lagae, Liesbet; Borghs, Gustaaf; Maes, Guido; Huo, Qun

    2010-11-12

    Combining the intriguing optical properties of gold nanoparticles with the inherent physical and dynamic properties of polymers can give rise to interesting hybrid nanomaterials. In this study, we report the synthesis of poly(acrylic acid) (PAA)-capped gold nanoparticles. The polyelectrolyte-wrapped gold nanoparticles were fully characterized and studied via a combination of techniques, i.e. UV-vis and infrared spectroscopy, dark field optical microscopy, SEM imaging, dynamic light scattering and zeta potential measurements. Although PAA-capped nanoparticles have been previously reported, this study revealed some interesting aspects of the colloidal stability and morphological change of the polymer coating on the nanoparticle surface in an electrolytic environment, at various pH values and at different temperatures.

  6. Quantification of Heteroaggregation between Citrate-Stabilized Gold Nanoparticles and Hematite Colloids.

    Science.gov (United States)

    Smith, Brian M; Pike, Daniel J; Kelly, Michael O; Nason, Jeffrey A

    2015-11-03

    Collisions with and attachment to natural colloids (heteroaggregation) is likely to influence significantly the fate, transport, and toxicity of engineered nanoparticles (ENPs). This study investigated heteroaggregation between hematite (α-Fe2O3) colloids and citrate-capped gold nanoparticles (Cit-AuNPs) using a novel approach involving time-resolved dynamic light scattering and parallel experiments designed to quantify nanoparticle attachment and heteroaggregate surface charge. Experiments were performed in low ionic strength synthetic water at environmentally relevant pH in the presence and absence of Suwannee River Natural Organic Matter (SRNOM). In the absence of SRNOM at pH values where Cit-AuNPs and hematite are oppositely charged, attachment efficiencies are high and Cit-AuNPs are capable of destabilizing hematite following an "electrostatic patch" mechanism. Furthermore, maximum observed surface coverages were far below those predicted by geometry alone, a fact predicted by the random sequential adsorption (RSA) model that has significant implications for the estimation of heteroaggregate attachment efficiencies. At pH values where both particles are negative or in the presence of small amounts of SRNOM, attachment was minimal. Calculated attachment efficiencies using the measured surface coverages corroborate these findings. The calculation of attachment efficiencies and the identification of mechanisms governing heteroaggregation represents an important step toward predicting the transport, fate, and toxicity of ENPs in the environment.

  7. Silver nanoparticles in complex biological media: assessment of colloidal stability and protein corona formation

    Science.gov (United States)

    Argentiere, Simona; Cella, Claudia; Cesaria, Maura; Milani, Paolo; Lenardi, Cristina

    2016-08-01

    Engineered silver nanoparticles (AgNPs) are among the most used nanomaterials in consumer products, therefore concerns are raised about their potential for adverse effects in humans and environment. Although an increasing number of studies in vitro and in vivo are being reported on the toxicity of AgNPs, most of them suffer from incomplete characterization of AgNPs in the tested biological media. As a consequence, the comparison of toxicological data is troublesome and the toxicity evaluation still remains an open critical issue. The development of a reliable protocol to evaluate interactions of AgNPs with surrounding proteins as well as to assess their colloidal stability is therefore required. In this regard, it is of importance not only to use multiple, easy-to-access and simple techniques but also to understand limitations of each characterization methods. In this work, the morphological and structural behaviour of AgNPs has been studied in two relevant biological media, namely 10 % FBS and MP. Three different techniques (Dynamic Light Scattering, Transmission Electron Microscopy, UV-Vis spectroscopy) were tested for their suitability in detecting AgNPs of three different sizes (10, 40 and 100 nm) coated with either citrate or polyvinylpyrrolidone. Results showed that UV-Vis spectroscopy is the most versatile and informative technique to gain information about interaction between AgNPs and surrounding proteins and to determine their colloidal stability in the tested biological media. These findings are expected to provide useful insights in characterizing AgNPs before performing any further in vitro/in vivo experiment.

  8. Gel formation in suspensions of oppositely charged colloids: mechanism and relation the equilibrium phase diagram

    NARCIS (Netherlands)

    Sanz, E.; Leunissen, M.E.; Fortini, A.; van Blaaderen, A.; Dijkstra, M.

    2008-01-01

    We study gel formation in a mixture of equally-sized oppositely charged colloids both experimentally and by means of computer simulations. Both the experiments and the simulations show that the mechanism by which a gel is formed from a dilute, homogeneous suspension is an interrupted gas-liquid phas

  9. Mechanisms of Fractal Formation in Colloidal Carbon-Bearing Natural System

    Directory of Open Access Journals (Sweden)

    A.P. Kuzmenko

    2013-12-01

    Full Text Available By using the advanced nano-approach processes and phenomena in self-organizing colloidal systems are studied. The conditions of appearance of self-organized phenomena are determined and also ranges of operation of diffusion, capillary, and fractalization mechanisms are found.

  10. Stabilization and Control of Rheological Properties of Fe2O3/Al(OH)(3)-rich Colloidal Slurries Under High Ionic Strength and pH

    Energy Technology Data Exchange (ETDEWEB)

    Chun, Jaehun; Poloski, Adam P.; Hansen, E. K.

    2010-08-01

    Controlling the stability and rheological properties of colloidal slurries has been an important but challenging issue for various applications such as cosmetics, ceramic processing, and nuclear waste treatment. For example, at the Department of Energy (DOE) Hanford and Savannah River sites, operation of the waste treatment facilities with increased solids loading affects waste processing rates but impacts the rheological properties. We investigated various rheological modifiers on a Fe2O3-rich nuclear waste simulant, characterized by high ionic strength and pH, in order to reduce rheological properties of the colloidal slurry. Rheological modifiers change particle interactions in colloidal slurries; they mainly alter the electrostatic and steric interactions between particles, leading to a change in rheological properties. Weak acid type rheological modifiers strengthen electrostatic repulsion whereas nonionic/polymer surfactant type rheological modifiers introduce a steric repulsion. Using rheological analysis, it was found that citric acid and polyacrylic acid are good rheological modifiers for the simulant tested, effectively reducing yield stresses by as much as 70%. Further analysis supports that addition of such rheological modifiers increases the stability of the slurry. Binding cations in bulk solution and adsorption on the surface of the particles are identified as a reasonable working mechanism for citric acid and polyacrylic acid.

  11. Effect of laundry surfactants on surface charge and colloidal stability of silver nanoparticles.

    Science.gov (United States)

    Skoglund, Sara; Lowe, Troy A; Hedberg, Jonas; Blomberg, Eva; Wallinder, Inger Odnevall; Wold, Susanna; Lundin, Maria

    2013-07-16

    The stability of silver nanoparticles (Ag NPs) potentially released from clothing during a laundry cycle and their interactions with laundry-relevant surfactants [anionic (LAS), cationic (DTAC), and nonionic (Berol)] have been investigated. Surface interactions between Ag NPs and surfactants influence their speciation and stability. In the absence of surfactants as well as in the presence of LAS, the negatively charged Ag NPs were stable in solution for more than 1 day. At low DTAC concentrations (≤1 mM), DTAC-Ag NP interactions resulted in charge neutralization and formation of agglomerates. The surface charge of the particles became positive at higher concentrations due to a bilayer type formation of DTAC that prevents from agglomeration due to repulsive electrostatic forces between the positively charged colloids. The adsorption of Berol was enhanced when above its critical micelle concentration (cmc). This resulted in a surface charge close to zero and subsequent agglomeration. Extended DLVO theory calculations were in compliance with observed findings. The stability of the Ag NPs was shown to depend on the charge and concentration of the adsorbed surfactants. Such knowledge is important as it may influence the subsequent transport of Ag NPs through different chemical transients and thus their potential bioavailability and toxicity.

  12. A Mechanism for the Self-Organization of Colloidal Gold Nanoparticles

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yong-Jun; HAN Guan-Qi; LI Wei; DAI Min; ZHANG Yu; HUANG Xin-Fan; CHEN Kun-Ji

    2004-01-01

    @@ We report a two-stage mechanism of formation of the two-dimensional surperlattices in colloidal gold nanoparticles. The first stage is the formation and growth of holes. When the film is thinner than the "pancake" thickness and because the solvent volatility holes nucleate and grow, the dry solid surface is exposed. The second stage corresponds to the reorganization of the colloids in the impacted areas between several holes, in which the particles gathering along the rims order due to the van der Waals-type attraction between colloids and the confinement by the length of dodecanethiol. Then at a compromised distance and perfect position giving the minimum free energy, ordering occurs in small domains along the boundary of the hole. When the ordered domains become closer because of the hole growth, they rotate at certain angles and the further ordering appears.

  13. MODIFICATION OF TRANSITION METAL CATIONS TO POLYMER- STABILIZED PLATINUM COLLOIDAL CLUSTERS IN ENANTIOSELECTIVE HYDROGENATION OF METHYL PYRUVATE

    Institute of Scientific and Technical Information of China (English)

    Xiao-ping Yan; Bao-lin He; Jie Zhang; Han-fan Liu

    2005-01-01

    Modification of transition metal cations to polymer-stabilized Pt colloidal clusters modified with cinchonidine was studied in enantioselective hydrogenation of methyl pyruvate. Compared to the enantiomeric excess (e.e.) value (71.4%)obtained without the presence of metal cations, obvious e.e. enhancement (up to 82.5%) was resulted from the addition of Zn2+ but with a certain decrease in activity. The reaction parameters in the presence of Zn2+ were also studied. It was found that the Pt colloidal catalysts in the presence of metal cations performed very differently from that in the absence of metal cations.

  14. Stability and structure of protein-lipoamino acid colloidal particles: toward nasal delivery of pharmaceutically active proteins.

    Science.gov (United States)

    Bijani, Christian; Arnarez, Clément; Brasselet, Sabrina; Degert, Corinne; Broussaud, Olivier; Elezgaray, Juan; Dufourc, Erick J

    2012-04-03

    To circumvent the painful intravenous injection of proteins in the treatment of children with growth deficiency, anemia, and calcium insufficiency, we investigated the stability and structure of protein-lipoamino acid complexes that could be nasally sprayed. Preparations that ensure a colloidal and structural stability of recombinant human growth hormone (rhGH), recombinant human erythropoietin (rhEPO), and salmon calcitonin (sCT) mixed with lauroyl proline (LP) were established. Protein structure was controlled by circular dichroism, and very small sizes of ca. 5 nm were determined by dynamic light scattering. The colloidal preparations could be sprayed with a droplet size of 20-30 μm. The molecular structure of aggregates was investigated by all-atom molecular dynamics. Whereas a lauroyl proline capping of globular proteins rhGH and rhEPO with preservation of their active structure was observed, a mixed micelle of sCT and lipoamino acids was formed. In the latter, aggregated LP constitutes the inner core and the surface is covered with calcitonins that acquire a marked α-helix character. Hydrophobic/philic interaction balance between proteins and LP drives the particles' stability. Passage through nasal cells grown at confluence was markedly increased by the colloidal preparations and could reach a 20 times increase in the case of EPO. Biological implications of such colloidal preparations are discussed in terms of furtiveness.

  15. Complex coacervation core micelles. Colloidal stability and aggregation mechanism

    NARCIS (Netherlands)

    Burgh, van der S.; Keizer, de A.; Cohen Stuart, M.A.

    2004-01-01

    Complex coacervation core micelles were prepared with various polyelectrolytes and oppositely charged diblock copolymers. The diblock copolymers consist of a charged block and a water-soluble neutral block. Our experimental technique was dynamic light scattering in combination with titrations. At

  16. Long term stability and reproducibility of magnetic colloids are key issues for steady values of Specific Power Absorption through time

    CERN Document Server

    Sanz, B; Cassinelli, N; Ibarra, M R; Goya, G F

    2016-01-01

    Virtually all clinical applications of magnetic nanoparticles (MNPs) require the formulation of biocompatible, water-based magnetic colloids. For magnetic hyperthermia, the requirements also include a high colloidal stability against precipitation and agglomeration of the constituent MNPs, in order to keep the heating efficiency of the ferrofluid in the long term. The specific power absorption (SPA) of single-domain MNPs depends critically on the average particle size and size distribution width, therefore first-rate reproducibility among different batches regarding these parameters are also needed. We have studied the evolution of the SPA of highly reproducible and stable water-based colloid composed of polymer coated $Fe_{3}O_{4}$ magnetic nanoparticles. By measuring the specific power absorption (SPA) values along one year as a function of field amplitude and frequencies ($H \\leq 24 kA/m$; $260 \\leq f \\leq 830 kHz$), we demonstrated that SPA in these samples can be made reproducible between successive synt...

  17. Superparamagnetic iron oxide/chitosan core/shells for hyperthermia application: Improved colloidal stability and biocompatibility

    Science.gov (United States)

    Patil, R. M.; Shete, P. B.; Thorat, N. D.; Otari, S. V.; Barick, K. C.; Prasad, A.; Ningthoujam, R. S.; Tiwale, B. M.; Pawar, S. H.

    2014-04-01

    Superparamagnetic magnetite nanoparticles are of great interest due to their potential biomedical applications. In the present investigation, Fe3O4 magnetic nanoparticles were prepared by alkaline precipitation using ferrous chloride as the sole source. An amphiphilic polyelectrolyte with the property of biocompatibility and functional carboxyl groups was used as a stabilizer to prepare a well-dispersed suspension of superparamagnetic Fe3O4 nanoparticles. The final material composed of Fe3O4 core and chitosan (CH) shell was produced. The amino groups of CH coated on Fe3O4 nanoparticles were further cross linked using glutaraldehyde (GLD) for stable coating. FTIR spectra, XPS and TGA confirmed the coating of CH/GLD on the surface of Fe3O4 nanoparticles. XRD patterns indicate the pure phase Fe3O4 with a spinel structure. The nanoparticles were superparamagnetic at room temperature with saturation magnetization values for bare and coated nanoparticles which were 51.68 emu/g and 48.60 emu/g, respectively. Zeta potential values showed higher colloidal stability of coated nanoparticles than the bare one. Cytotoxicity study up to 2 mg mL-1 concentration showed no drastic change in cell viability of nanoparticles after coating. Also, coated nanoparticles showed increased SAR value, making them suitable for hyperthermia therapy application.

  18. Silver colloidal nanoparticle stability: influence on Candida biofilms formed on denture acrylic.

    Science.gov (United States)

    Monteiro, Douglas Roberto; Takamiya, Aline Satie; Feresin, Leonardo Perina; Gorup, Luiz Fernando; de Camargo, Emerson Rodrigues; Delbem, Alberto Carlos Botazzo; Henriques, Mariana; Barbosa, Debora Barros

    2014-08-01

    Our aim in this study was to evaluate how the chemical stability of silver nanoparticles (SNs) influences their efficacy against Candida albicans and C. glabrata biofilms. Several parameters of SN stability were tested, namely, temperature (50ºC, 70ºC, and 100ºC), pH (5.0 and 9.0), and time of contact (5 h and 24 h) with biofilms. The control was defined as SNs without temperature treatment, pH 7, and 24 h of contact. These colloidal suspensions at 54 mg/L were used to treat mature Candida biofilms (48 h) formed on acrylic. Their efficacy was determined by total biomass and colony-forming unit quantification. Data were analyzed using analysis of variance and the Bonferroni post hoc test (α = 0.05). The temperature and pH variations of SNs did not affect their efficacy against the viable cells of Candida biofilms (P > 0.05). Moreover, the treatment periods were not decisive in terms of the susceptibility of Candida biofilms to SNs. These findings provide an important advantage of SNs that may be useful in the treatment of Candida-associated denture stomatitis.

  19. Transport and regulation mechanism of the colloidal gold liposomes in the brain microvascular endothelial cells

    Institute of Scientific and Technical Information of China (English)

    WANG Lipeng; CHANG Yanzhong

    2015-01-01

    Objective:Blood-brain barrier is the key barrier of brain in the innate immune. It can prevent the harmful substances from the blood into the brain. In order to keep the brain in a relatively stable environment and maintain the normal function of the nervous system, it can also pump harmful substances or excess substances outside the brain selectively. Among them, brain microvascular endothelial cell tissue is a key part in the blood-brain barrier's function. The number of the patients with central nervous system ( CNS) diseases increased year by year. The therapeutic drug is usually inhibited by the blood-brain barrier and is difficult to work. Therefore, how to modify the drug and to make it easier to cross the blood brain barrier is the key point to cure CNS. At present, more than 95% research focus only on how nano drugs can enter the cell, the way and efficiency to enter the cell and the research of effect of nano drug etc. For the process of drug carrier in endocytosis, intracellular transport and release and regulation of research are rarely reported. Clathrin and P-glycoprotein are related protein in endo-cytosis and exocytosis with nano drug. Clathrin is located on the plasma membrane. It participates in endocytosis of some nutrients, and maybe the entry into the cell of some drugs. P-glycoprotein is located in the membrane of cer-ebral capillary endothelial cells. It can efflux drugs relying on ATP. Although there is a certain understanding of the cell in the inner swallow and efflux. But the process of the liposome drug is not clear. To solve the above prob-lems, using colloidal gold liposome nano materials to trace liposome's transport and regulation mechanism in brain microvascular endothelial cells, and study endocytosis, release, distribution and regulation mechanism of nano lipo-somes in brain microvascular. The solution of this problem can guide to construct reasonable drug carrier, and look forward to clarifing the molecular basis and mechanism of

  20. Hard sphere colloidal dispersions: Mechanical relaxation pertaining to thermodynamic forces

    NARCIS (Netherlands)

    Mellema, J.; Kruif, de C.G.; Blom, C.; Vrij, A.

    1987-01-01

    The complex viscosity of sterically stabilized (hard) silica spheres in cyclohexane has been measured between 80 Hz and 170 kHz with torsion pendulums and a nickel tube resonator. The observed relaxation behaviour can be attributed to the interplay of hydrodynamic and thermodynamic forces. The valid

  1. Aggregation and stability of anisotropic charged clay colloids in aqueous medium in the presence of salt.

    Science.gov (United States)

    Ali, Samim; Bandyopadhyay, Ranjini

    2016-01-01

    Na-montmorillonite nanoclay is a colloid of layered mineral silicate. When dispersed in water, this mineral swells on absorption of water and exfoliates into platelets with electric double layers on their surfaces. Even at low particle concentration, the aqueous dispersion can exhibit a spontaneous ergodicity breaking phase transition from a free flowing liquid to nonequilibrium, kinetically arrested and disordered states such as gels and glasses. In an earlier publication [Applied Clay Science, 2015, 114, 8592], we showed that the stability of clay gels can be enhanced by adding a salt later to the clay dispersion prepared in deionized water, rather than by adding the clay mineral to a previously mixed salt solution. Here, we directly track the collapsing interface of sedimenting clay gels using an optical method and show that adding salt after dispersing the clay mineral does indeed result in more stable gels even in very dilute dispersions. These weak gels are seen to exhibit a transient collapse after a finite delay time, a phenomenon observed previously in depletion gels. The velocity of the collapse oscillates with the age of the sample. However, the average velocity of collapse increases with sample age up to a peak value before decreasing at higher ages. With increasing salt concentration, the delay time for transient collapse decreases, while the peak value of the collapsing velocity increases. Using ultrasound attenuation spectroscopy, rheometry and cryogenic scanning electron microscopy, we confirm that morphological changes of the gel network assembly, facilitated by thermal fluctuations, lead to the observed collapse phenomenon. Since clay minerals are used extensively in polymer nanocomposites, as rheological modifiers, stabilizers and gas absorbents, we believe that the results reported in this work are extremely useful for several practical applications and also for understanding geophysical phenomena such as the formation and stability of quicksand

  2. Evaluation of Colloidal Stability and Ecotoxicity of Metal-based Nanoparticles in the Aquatic and Terrestrial Systems

    Science.gov (United States)

    Pokhrel, Lok Raj

    Intrinsic to the many nano-enabled products are atomic-size multifunctional engineered nanomaterials, which upon release contaminate the environments, raising considerable health and safety concerns. This Ph.D. dissertation is designed to investigate (i) whether metals or oxide nanoparticles are more toxic than ions, and if MetPLATE(TM) bioassay is applicable as a rapid nanotoxicity screening tool; (ii) how variable water chemistry (dissolved organic carbon (DOC), pH, and hardness) and organic compounds (cysteine, humic acid, and trolox) modulate colloidal stability, ion release, and aquatic toxicity of silver nanoparticles (AgNP); and (iii) the developmental responses of crop plants exposed to Ag- or ZnO- (zinc oxide) nanoparticles. Results suggest that the MetPLATE can be considered a high-throughput screening tool for rapid nanotoxicity evaluation. Detectable changes in the colloidal diameter, surface charge, and plasmonic resonance revealed modulating effects of variable water chemistry and organic ligands on the particle stability, dissolution, and toxicity of AgNPs against Escherichia coli or Daphnia magna. Silver dissolution increased as a function of DOC concentrations but decreased with increasing hardness, pH, cysteine, or trolox levels. Notably, the dissociated Ag+ was inadequate to explain AgNP toxicity, and that the combined effect of AgNPs and dissolved Ag+ under each ligand treatment was lower than of AgNO 3. Significant attenuation by trolox signifies an oxidative stress-mediated AgNP toxicity; its inability to attenuate AgNO3 toxicity, however, negates oxidative stress as Ag+ toxicity mechanism, and that cysteine could effectively quench free Ag+ to alleviate AgNO 3 toxicity in D. magna. Surprisingly, DOC-AgNPs complex that apparently formed at higher DOC levels might have led daphnids filter-feed on aggregates, potentially elevating internal dose, and thus higher mortality. Maize root anatomy showed differential alterations upon exposure to Ag

  3. Charge inversion and colloidal stability of carbon black in battery electrolyte solutions

    NARCIS (Netherlands)

    Zhang, Y.; Narayanan, A.; Mugele, F.; Cohen Stuart, M.A.; Duits, M.H.G.

    2016-01-01

    Colloids and Surfaces A: Physicochemical and Engineering Aspects is an international journal devoted to the science of the fundamentals, engineering fundamentals, and applications of colloidal and interfacial phenomena and processes. The journal aims at publishing research papers of high quality and

  4. Thermal Stability and Anisotropic Sublimation of Two-Dimensional Colloidal Bi2Te3 and Bi2Se3 Nanocrystals

    CERN Document Server

    Buha, Joka; Castillo, Antonio Esau Del Rio; Bonaccorso, Francesco; Manna, Liberato

    2016-01-01

    The structural and compositional stabilities of two dimensional 2D Bi2Te3 and Bi2Se3 nanocrystals, produced by both colloidal synthesis and by liquid phase exfoliation, were studied by in situ transmission electron microscopy TEM during annealing at temperatures between 350 and 500 C. The sublimation process induced by annealing is structurally and chemically anisotropic and takes place through the preferential dismantling of the prismatic 011-0 type planes, and through the preferential sublimation of Te or Se.

  5. Impacts of select organic ligands on the colloidal stability, dissolution dynamics, and toxicity of silver nanoparticles.

    Science.gov (United States)

    Pokhrel, Lok R; Dubey, Brajesh; Scheuerman, Phillip R

    2013-11-19

    Key understanding of potential transformations that may occur on silver nanoparticle (AgNP) surface upon interaction with naturally ubiquitous organic ligands (e.g., -SH (thoil), humic acid, or -COO (carboxylate)) is limited. Herein we investigated how dissolved organic carbon (DOC), -SH (in cysteine, a well-known Ag(+) chelating agent), and -COO (in trolox, a well-known antioxidant) could alter the colloidal stability, dissolution rate, and toxicity of citrate-functionalized AgNPs (citrate-AgNPs) against a keystone crustacean Daphnia magna. Cysteine, DOC, or trolox amendment of citrate-AgNPs differentially modified particle size, surface properties (charge, plasmonic spectra), and ion release dynamics, thereby attenuating (with cysteine or trolox) or promoting (with DOC) AgNP toxicity. Except with DOC amendment, the combined toxicity of AgNPs and released Ag under cysteine or trolox amendment was lower than of AgNO3 alone. The results of this study show that citrate-AgNP toxicity can be associated with oxidative stress, ion release, and the organism biology. Our evidence suggests that specific organic ligands available in the receiving waters can differentially surface modify AgNPs and alter their environmental persistence (changing dissolution dynamics) and subsequently the toxicity; hence, we caveat to generalize that surface modified nanoparticles upon environmental release may not be toxic to receptor organisms.

  6. Effect of Extracellular Polymeric Substances on CuO Nanoparticle Dissolution and Colloidal Stability

    Science.gov (United States)

    Adeleye, A. S.; Keller, A. A.

    2013-12-01

    Extracellular polymeric substances (EPS) are high molecular weight polymers produced by microorganisms growing in natural as well as artificial environments. EPS may interact with engineered nanomaterials (ENMs) in aquatic systems via electrostatic and/or hydrophobic associations, therefore, influencing the fate and transport of ENMs. In this study the effect of soluble EPS isolated from Isochrysis galbana, a marine phytoplankton, on the dissolution kinetics and colloidal stability of CuO nanoparticles was investigated. EPS was characterized by measuring hydrodynamic diameter, total organic carbon, carbohydrate, and protein concentrations. CuO nanoparticles were more stable in the presence of EPS in aqueous media as indicated by hydrodynamic size and average count rate measurements. The effect of pH and ionic strength on dissolution was also studied. [Cu2+] and [Cu]total detected after a week were 5.70 mg L-1 and 7.08 mg L-1 respectively when 10 mg L-1 CuO nanoparticles was kept in 10 mM NaCl at pH 4. In the presence of 5 mg-C EPS L-1, [Cu2+] and [Cu]total were slightly lower at 5.0 mg L-1 and 5.53 mg L-1 respectively. Although observed [Cu2+] and [Cu]total were significantly lower at neutral and alkaline pH conditions, a similar pattern was observed.

  7. Colloid retention mechanisms in single, saturated, variable-aperture fractures.

    Science.gov (United States)

    Rodrigues, S N; Dickson, S E; Qu, J

    2013-01-01

    The characterization of fractured aquifers is commonly limited to the methodologies developed for unconsolidated porous media aquifers, which results in many uncertainties. Recent work indicates that fractured rocks remove more particulates than they are conventionally credited for. This research was designed to quantify the number of Escherichia coli RS2-GFP retained in single, saturated, variable-aperture fractures extracted from the natural environment. Conservative solute and E. coli RS2-GFP tracer experiments were used to elucidate the relationships between dominant retention mechanisms, aperture field characteristics, and flow rate. A non-destructive method of determining a surrogate measure of a coefficient of variation (COV(S)) for each fracture was used to better understand the transport behaviour of E. coli RS2-GFP. The results from this research all point to the importance of aperture field characterization in understanding the fate and transport of contaminants in fractured aquifers. The mean aperture was a very important characteristic in determining particulate recovery, so were matrix properties, COV(s), and flow rate. It was also determined that attachment is a much more significant retention mechanism than straining under the conditions employed in this research. Finally, it was demonstrated that the dominant retention mechanism in a fracture varies depending on the specific discharge. An improved understanding of the mechanisms that influence the fate and transport of contaminants through fractures will lead to the development of better tools and methodologies for the characterization of fractured aquifers, as well as the ability to manipulate the relevant mechanisms to increase or decrease retention, depending on the application.

  8. Mechanical properties of stabilized artificial organic soil

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In order to study the influence of organic matter on the mechanical properties of stabilized soil and the effect of XGL2005 on stabilizing organic soil,unconfined compressive strength tests were carried out.Test results indicated that the strength of stabilized soil decreased in the form of a logarithmic function as the organic matter content increased.In contrast,the strength increased in the form of a power function as the content of the stabilization agent increased.The strength of cement stabilized organic soil was reinforced greatly by adding the stabilizer XGL2005.Based on the law obtained from the test,a strength prediction model was established by regression analysis.The model included the influence of the curing time,the content of the cement,the organic matter content and the stabilization agent on the strength of stabilized soil.

  9. Functional PEG-PAMAM-tetraphosphonate capped NaLnF₄ nanoparticles and their colloidal stability in phosphate buffer.

    Science.gov (United States)

    Zhao, Guangyao; Tong, Lemuel; Cao, Pengpeng; Nitz, Mark; Winnik, Mitchell A

    2014-06-17

    Developing surface coatings for NaLnF4 nanoparticles (NPs) that provide long-term stability in solutions containing competitive ions such as phosphate remains challenging. An amine-functional polyamidoamine tetraphosphonate (NH2-PAMAM-4P) as a multidentate ligand for these NPs has been synthesized and characterized as a ligand for the surface of NaGdF4 and NaTbF4 nanoparticles. A two-step ligand exchange protocol was developed for introduction of the NH2-PAMAM-4P ligand on oleate-capped NaLnF4 NPs. The NPs were first treated with methoxy-poly(ethylene glycol)-monophosphoric acid (M(n) = 750) in tetrahydrofuran. The mPEG750-OPO3-capped NPs were stable colloidal solutions in water, where they could be ligand-exchanged with NH2-PAMAM-4P. The surface amine groups on the NPs were available for derivatization to attach methoxy-PEG (M(n) = 2000) and biotin-terminated PEG (M(n) = 2000) chains. The surface coverage of ligands on the NPs was examined by thermal gravimetric analysis, and by a HABA analysis for biotin-containing NPs. Colloidal stability of the NPs was examined by dynamic light scattering. NaGdF4 and NaTbF4 NPs capped with mPEG2000-PAMAM-4P showed colloidal stability in DI water and in phosphate buffer (10 mM, pH 7.4). A direct comparison with NaTbF4 NPs capped with a mPEG2000-lysine-based tetradentate ligand that we reported previously (Langmuir 2012, 28, 12861-12870) showed that both ligands provided long-term stability in phosphate buffer, but that the lysine-based ligand provided better stability in phosphate-buffered saline.

  10. On Stability of the Mechanical Lagrangian Systems

    Directory of Open Access Journals (Sweden)

    Valer Niminet

    2011-12-01

    Full Text Available

    We consider MLS (mechanical Lagrangian systems with
    external forces. We give some conditions of stability and dissipativity and show that the energy of the system decreases on the integral curves.


    Key words: LMS, stability, dissipative system.

  11. Stable colloids in molten inorganic salts

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hao; Dasbiswas, Kinjal; Ludwig, Nicholas B.; Han, Gang; Lee, Byeongdu; Vaikuntanathan, Suri; Talapin, Dimitri V.

    2017-02-16

    A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes1, 2, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other2. Electrostatic stabilization3, 4 of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains2, 5. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute–solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute–solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

  12. Test of the diffusing-diffusivity mechanism using near-wall colloidal dynamics

    CERN Document Server

    Matse, Mpumelelo

    2016-01-01

    The diffusing-diffusivity mechanism proposed by Chubynsky and Slater [PRL 113, 098302, 2014] predicts that, in environments where the diffusivity changes gradually, the displacement distribution becomes non-Gaussian, even though the mean-squared displacement (MSD) grows linearly with time. Here, we report single-particle tracking measurements of the diffusion of colloidal spheres near a planar wall. Because the local effective diffusivity is known, we have been able to carry out the first direct test of this mechanism for diffusion in inhomogeneous media.

  13. Superparamagnetic iron oxide nanoparticles incorporated into silica nanoparticles by inelastic collision via ultrasonic field: Role of colloidal stability

    Energy Technology Data Exchange (ETDEWEB)

    Sodipo, Bashiru Kayode; Azlan, Abdul Aziz [Nano-Optoelectronics Research and Technology (NOR) Lab, School of Physics, Universiti Sains Malaysia, 11800 Pulau Pinang, Malaysia Nano-Biotechnology Research (Malaysia); Innovation (NanoBRI), Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia, 11800, Pulau Pinang (Malaysia)

    2015-04-24

    Superparamagnetic iron oxide nanoparticles (SPION)/Silica composite nanoparticles were prepared by ultrasonically irradiating colloidal suspension of silica and SPION mixture. Both silica and SPION were synthesized independently via co-precipitation and sol-gel method, respectively. Their mixtures were sonicated at different pH between 3 and 5. Electrophoresis measurement and other physicochemical analyses of the products demonstrate that at lower pH SPION was found incorporated into the silica. However, at pH greater than 4, SPION was unstable and unable to withstand the turbulence flow and shock wave from the ultrasonic field. Results suggest that the formation of the SPION/silica composite nanoparticles is strongly related to the inelastic collision induced by ultrasonic irradiation. More so, the formation the composite nanoparticles via the ultrasonic field are dependent on the zeta potential and colloidal stability of the particles.

  14. Evaluation of effects of pH and ionic strength on colloidal stability of IgG solutions by PEG-induced liquid-liquid phase separation

    Science.gov (United States)

    Thompson, Ronald W.; Latypov, Ramil F.; Wang, Ying; Lomakin, Aleksey; Meyer, Julie A.; Vunnum, Suresh; Benedek, George B.

    2016-11-01

    Colloidal stability of IgG antibody solutions is important for pharmaceutical and medicinal applications. Solution pH and ionic strength are two key factors that affect the colloidal stability of protein solutions. In this work, we use a method based on the PEG-induced liquid-liquid phase separation to examine the effects of pH and ionic strength on the colloidal stability of IgG solutions. We found that at high ionic strength (≥0.25M), the colloidal stability of most of our IgGs is insensitive to pH, and at low ionic strength (≤0.15M), all IgG solutions are much more stable at pH 5 than at pH 7. In addition, the PEG-induced depletion force is less efficient in causing phase separation at pH 5 than at pH 7. In contrast to the native inter-protein interaction of IgGs, the effect of depletion force on phase separation of the antibody solutions is insensitive to ionic strength. Our results suggest that the long-range electrostatic inter-protein repulsion at low ionic strength stabilizes the IgG solutions at low pH. At high ionic strength, the short-range electrostatic interactions do not make a significant contribution to the colloidal stability for most IgGs with a few exceptions. The weaker effect of depletion force at lower pH indicates a reduction of protein concentration in the condensed phase. This work advances our basic understanding of the colloidal stability of IgG solutions and also introduces a practical approach to measuring protein colloidal stability under various solution conditions.

  15. Evaluation of effects of pH and ionic strength on colloidal stability of IgG solutions by PEG-induced liquid-liquid phase separation.

    Science.gov (United States)

    Thompson, Ronald W; Latypov, Ramil F; Wang, Ying; Lomakin, Aleksey; Meyer, Julie A; Vunnum, Suresh; Benedek, George B

    2016-11-14

    Colloidal stability of IgG antibody solutions is important for pharmaceutical and medicinal applications. Solution pH and ionic strength are two key factors that affect the colloidal stability of protein solutions. In this work, we use a method based on the PEG-induced liquid-liquid phase separation to examine the effects of pH and ionic strength on the colloidal stability of IgG solutions. We found that at high ionic strength (≥0.25M), the colloidal stability of most of our IgGs is insensitive to pH, and at low ionic strength (≤0.15M), all IgG solutions are much more stable at pH 5 than at pH 7. In addition, the PEG-induced depletion force is less efficient in causing phase separation at pH 5 than at pH 7. In contrast to the native inter-protein interaction of IgGs, the effect of depletion force on phase separation of the antibody solutions is insensitive to ionic strength. Our results suggest that the long-range electrostatic inter-protein repulsion at low ionic strength stabilizes the IgG solutions at low pH. At high ionic strength, the short-range electrostatic interactions do not make a significant contribution to the colloidal stability for most IgGs with a few exceptions. The weaker effect of depletion force at lower pH indicates a reduction of protein concentration in the condensed phase. This work advances our basic understanding of the colloidal stability of IgG solutions and also introduces a practical approach to measuring protein colloidal stability under various solution conditions.

  16. On the mechanisms of colloidal self-assembly during spin-coating.

    Science.gov (United States)

    Toolan, Daniel T W; Fujii, Syuji; Ebbens, Stephen J; Nakamura, Yoshinobu; Howse, Jonathan R

    2014-11-28

    Spin-coating offers a facile fabrication route for the production of high quality colloidal crystals, which have potential as photonic band-gap materials. This paper presents the results of direct observations of the self-assembly of latex colloids during spin-coating through the use of stroboscopic microscopy. We have been able to identify several mechanisms by which self-assembly occurs, depending upon the dispersion properties, such as particle weight fraction, solvent volatility and viscosity. Through the use of stroboscopic microscopy we have directly observed ordering occurring due to high concentrations of colloid particles (where volatility is relatively low), resulting in the formation of regular close packed ordered particle arrays. Conversely when the system in spun-cast from a much more volatile solvent, highly disordered non-equilibrium arrangements of particles form. When spin-coating a low concentration, low volatility dispersion, ordering is dominated by the occurrence of capillary drying fronts, which drag the particles into ordered arrangements. At a volatility intermediate to that of water and ethanol, ordering occurring predominantly via shear forces. Finally when the volatility is increased beyond the shear ordering regime, excessive shear leads to the occurrence of drying fronts within the system and so again, capillary forces induce a large degree of order within the final film.

  17. KAM Stability and Celestial Mechanics

    CERN Document Server

    Celletti, A

    2004-01-01

    KAM theory is a powerful tool apt to prove perpetual stability in Hamiltonian systems, which are a perturbation of integrable ones. The smallness requirements for its applicability are well known to be extremely stringent. A long standing problem, in this context, is the application of KAM theory to ``physical systems" for ``observable" values of the perturbation parameters. Here, we consider the Restricted, Circular, Planar, Three-Body Problem (RCPTBP),i.e., the problem of studying the planar motions of a small body subject to the gravitational attraction of two primary bodies revolving on circular Keplerian orbits (which are assumed not to be influenced by the small body). When the mass ratio of the two primary bodies is small the RCPTBP is described by a nearly-integrable Hamiltonian system with two degrees of freedom; in a region of phase space corresponding to nearly elliptical motions with non small eccentricities, the system is well described by Delaunay variables. The Sun-Jupiter observed motion is ne...

  18. Stability and minimum size of colloidal clusters on a liquid-air interface.

    Science.gov (United States)

    Pergamenshchik, V M

    2012-02-01

    A vertical force applied to each of two colloids, trapped at a liquid-air interface, induces their logarithmic pairwise attraction. I recently showed [Phys. Rev. E 79, 011407 (2009)] that in clusters of size R much larger than the capillary length λ, the attraction changes to that of a power law and is much stronger due to a many-body effect, and I derived two equations that describe the equilibrium coarse-grained meniscus profile and colloid density in such clusters. In this paper, this theory is shown also to describe small clusters with R≪ λ provided the number N of colloids therein is sufficiently large. An analytical solution for a small circular cluster with an arbitrary short-range power-law pairwise repulsion is found. The energy of a cluster is obtained as a function of its radius R and colloid number N. As in large clusters, the attraction force and energy universally scale with the distance L between colloids as L(-3) and L(-2), respectively, for any repulsion forces. The states of an equilibrium cluster, predicted by the theory, are shown to be stable with respect to small perturbations of the meniscus profile and colloid density. The minimum number of colloids in a circular cluster, which sustains the thermal motion, is estimated. For standard parameters, it can be very modest, e.g., in the range 20-200, which is in line with experimental findings on reversible clusterization on a liquid-air interface. © 2012 American Physical Society

  19. Lysozyme adsorption on the colloidal chromium(III) oxide surface: Its impact on the system stability

    Energy Technology Data Exchange (ETDEWEB)

    Szewczuk-Karpisz, Katarzyna, E-mail: k.szewczuk-karpisz@wp.pl; Wiśniewska, Małgorzata; Myśliwiec, Dawid

    2015-08-30

    Highlights: • Lysozyme adsorption mechanism on the chromium(III) oxide surface was determined. • Surface charge density as well as zeta potential of Cr{sub 2}O{sub 3} particles were measured. • Turbidimetric method was used to estimate the suspension stability. • Depending on the pH value, lysozyme increases or decreases the system stability. - Abstract: This paper describes the lysozyme (LSZ) presence effect on the chromium(III) oxide (Cr{sub 2}O{sub 3}) suspension stability. First, the electrokinetic properties of the examined system, i.e. surface charge density and zeta potential of solid particles in the absence and presence of LSZ, were determined. The lysozyme addition reduces the metal oxide surface charge, which may be related to the interaction of the LSZ protonated amino groups with the adsorbent surface moieties. The LSZ macromolecules undergo adsorption on the Cr{sub 2}O{sub 3} surface only under electrostatic attraction. At the LSZ concentrations above 50 ppm the macromolecules cover completely the particle surface, which is evidenced by the observed zeta potential values. The LSZ influence on the Cr{sub 2}O{sub 3} suspension stability depends on the solution pH value. At pH 3, 4.6 and 7.6, the LSZ addition improves the system stability. In turn, at pH 9 it is associated with the slight suspension destabilization.

  20. Mechanical stability of iron under hydrostatic stresses

    Science.gov (United States)

    Mishra, K. L.; Thakur, O. P.; Thakur, K. P.

    1991-09-01

    A comprehensive investigation of the mechanics of iron subjected to arbitrary fluid pressure has been carried out. Apart from the classical elastic moduli ( k, μ, and μ') and conventional elastic moduli (Green and stretch moduli) computations are carried out for a family of generalised moduli of which the conventional moduli are just specific members. With the generalised moduli the mechanical stability of iron is investigated through Born criteria. It is found that classical stability, Green stability and stretch stability are all represented uniquely by the present generalised scheme. The definition of effective classical moduli under stresses enabled the amalgamation of the Born criteria of lattice stability into the single classical criteria of lattice stability of cubic crystal under hydrostatic loading environment. Computations are also carried out to investigate the coordinate and stress dependence of Young's modulus of elasticity, Poisson's ratio, mean velocity of elastic wave, and Debye temperature. Surprisingly, it is found that all these properties of solids play an important role in representing the mechanical stability of the solid. The path of uniaxial loading of iron is also investigated along with its internal energy variation on this path. This indicated the existance of stress-free fcc phase of iron on the path of uniaxial deformation at cell length a=3.6444 Å giving enthalpy of transformation (bcc→fcc) of 1.1 kJ/mol in good agreement with experimental results.

  1. [Toxicological evaluation of colloidal nano-sized silver stabilized polyvinylpyrrolidone. III. Enzymological, biochemical markers, state of antioxidant defense system].

    Science.gov (United States)

    Gmoshinsky, I V; Shipelin, V A; Vorozhko, I V; Sentsova, T B; Soto, S Kh; Avren'eva, L I; Guseva, G V; Kravchenko, L V; Khotimchenko, S A; Tutelyan, V A

    2016-01-01

    Nanosized colloidal silver (NCS) with primary nanoparticles (NPs) size in the range of 10-80 nm in aqueous suspension was administered to rats with initial weight 80±10 gfor the first 30 day intragastrically and for lasting 62 days with the diet consumed in doses of 0.1; 1.0 and 10 mg/kg of body weight b.w) per day based on silver (Ag). The control animals received deionized water and carrier of NPs - aqueous solution of stabilizer polyvinylpyrrolidone. Activity (Vmax) was determined in liver of microsomal mixed function monooxygenase isoforms CYP 1A1, 1A2 and 2B1 against their specific substrates, the activity of liver conjugating enzymes (glutathione-S-transferase and UDP-glucuronosyltransferase) in the microsomal fraction and a cytosol, and the overall and non-sedimentable activities of lysosomal hydrolases. In blood plasma there were evaluated malonic dialdehyde, PUFA diene conjugates, in erythrocytes - the activity of antioxidant enzymes. A set of standard biochemical indicators of blood serum was also determined. The studies revealed changes in a number of molecular markers of toxic action. Among them - the increase in the activity of key enzymes I and II stages of detoxification of xenobiotics, indicating its functional overvoltage; reducing the activity of glutathione peroxidase (GP), the total arylsulfatase A and B, β-galactosidase (in the absence of changes in their non-sedimentable activity), levels of uric acid, increased alkaline phosphatase activity. These changes occurred mainly at the dose Ag of 10 mg/kg b.w., except for the GP to which the threshold dose was 1 mg/kg b.w. No significant changes in the studied markers in a dose Ag 0,1 mg/kg b.w. were identified. Possible mechanisms of the toxic action of silver NPs are discussed.

  2. Thermal Stability and Anisotropic Sublimation of Two-Dimensional Colloidal Bi2Te3 and Bi2Se3 Nanocrystals.

    Science.gov (United States)

    Buha, Joka; Gaspari, Roberto; Del Rio Castillo, Antonio Esau; Bonaccorso, Francesco; Manna, Liberato

    2016-07-13

    The structural and compositional stabilities of two-dimensional (2D) Bi2Te3 and Bi2Se3 nanocrystals, produced by both colloidal synthesis and by liquid phase exfoliation, were studied by in situ transmission electron microscopy (TEM) during annealing at temperatures between 350 and 500 °C. The sublimation process induced by annealing is structurally and chemically anisotropic and takes place through the preferential dismantling of the prismatic {011̅0} type planes, and through the preferential sublimation of Te (or Se). The observed anisotropic sublimation is independent of the method of nanocrystal's synthesis, their morphology, or the presence of surfactant molecules on the nanocrystals surface. A thickness-dependent depression in the sublimation point has been observed with nanocrystals thinner than about 15 nm. The Bi2Se3 nanocrystals were found to sublimate below 280 °C, while the Bi2Te3 ones sublimated at temperatures between 350 and 450 °C, depending on their thickness, under the vacuum conditions in the TEM column. Density functional theory calculations confirm that the sublimation of the prismatic {011̅0} facets is more energetically favorable. Within the level of modeling employed, the sublimation occurs at a rate about 700 times faster than the sublimation of the {0001} planes at the annealing temperatures used in this work. This supports the distinctly anisotropic mechanisms of both sublimation and growth of Bi2Te3 and Bi2Se3 nanocrystals, known to preferentially adopt a 2D morphology. The anisotropic sublimation behavior is in agreement with the intrinsic anisotropy in the surface free energy brought about by the crystal structure of Bi2Te3 or Bi2Se3.

  3. A Cosmological Mechanism for Stabilizing Moduli

    CERN Document Server

    Huey, G; Ovrut, B A; Waldram, D; Huey, Greg; Steinhardt, Paul J.; Ovrut, Burt A.; Waldram, Daniel

    2000-01-01

    In this paper, we show how the generic coupling of moduli to the kinetic energy of ordinary matter fields results in a cosmological mechanism that influences the evolution and stability of moduli. As an example, we reconsider the problem of stabilizing the dilaton in a non-perturbative potential induced by gaugino condensates. A well-known difficulty is that the potential is so steep that the dilaton field tends to overrun the correct minimum and to evolve to an observationally unacceptable vacuum. We show that the dilaton coupling to the thermal energy of matter fields produces a natural mechanism for gently relaxing the dilaton field into the correct minimum of the potential without fine-tuning of initial conditions. The same mechanism is potentially relevant for stabilizing other moduli fields.

  4. Stabilization of plutonium nano-colloids by epitaxial distortion on mineral surfaces.

    Science.gov (United States)

    Powell, Brian A; Dai, Zurong; Zavarin, Mavrik; Zhao, Pihong; Kersting, Annie B

    2011-04-01

    The subsurface migration of Pu may be enhanced by the presence of colloidal forms of Pu. Therefore, complete evaluation of the risk posed by subsurface Pu contamination needs to include a detailed physical/chemical understanding of Pu colloid formation and interactions of Pu colloids with environmentally relevant solid phases. Transmission electron microscopy (TEM) was used to characterize Pu nanocolloids and interactions of Pu nanocolloids with goethite and quartz. We report that intrinsic Pu nanocolloids generated in the absence of goethite or quartz were 2-5 nm in diameter, and both electron diffraction analysis and HRTEM confirm the expected Fm3m space group with the fcc, PuO2 structure. Plutonium nanocolloids formed on goethite have undergone a lattice distortion relative to the ideal fluorite-type structure, fcc, PuO2, resulting in the formation of a bcc, Pu4O7 structure. This structural distortion results from an epitaxial growth of the plutonium colloid on goethite, leading to stronger binding of plutonium to goethite compared with other minerals such as quartz, where the distortion was not observed. This finding provides new insight for understanding how molecular-scale behavior at the mineral-water interface may facilitate transport of plutonium at the field scale.

  5. Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

    Directory of Open Access Journals (Sweden)

    Riccardo Scarfiello

    2016-12-01

    , will be described, revisited and critically interpreted within the framework of the currently understood mechanisms of colloidal heteroepitaxy.

  6. A global approach of the mechanism involved in the biosynthesis of gold colloids using micro-algae

    Science.gov (United States)

    Dahoumane, Si Amar; Yéprémian, Claude; Djédiat, Chakib; Couté, Alain; Fiévet, Fernand; Coradin, Thibaud; Brayner, Roberta

    2014-10-01

    The use of micro-algae for the production of noble metal nanoparticles has drawn much attention recently. This paper aims to address some questions raised by our earlier publications and some recent reports from other groups, among which the biological pathways involved in the bioreduction of noble metal cations into nanoparticles and the design of stable colloids. TEM micrographs, taken at the early stage of contact between cells and salt solutions, show undoubtedly that the biomineralization process occurs within the thylakoidal membranes, which are the organelles responsible for photosynthesis. We strongly believe that the available enzymes and their cofactors (enzymatic machinery) are the key molecules that allow such reduction, promoting therefore the formation of nanoparticles. In addition, by comparing the characteristics of gold colloids made by polysaccharides-producing and non-producing micro-algae strains, we demonstrate that the stability of those colloids is ensured predominantly by those biopolymers. These macrobiomolecules control partly the size and the shape of NPs.

  7. Mechanical stability of bipolar spindle assembly

    CERN Document Server

    Malgaretti, Paolo

    2016-01-01

    Assembly and stability of mitotic spindle is governed by the interplay of various intra-cellular forces, e.g. the forces generated by motor proteins by sliding overlapping anti-parallel microtubules (MTs) polymerized from the opposite centrosomes, the interaction of kinetochores with MTs, and the interaction of MTs with the chromosomes arms. We study the mechanical behavior and stability of spindle assembly within the framework of a minimal model which includes all these effects. For this model, we derive a closed--form analytical expression for the force acting between the centrosomes as a function of their separation distance and we show that an effective potential can be associated with the interactions at play. We obtain the stability diagram of spindle formation in terms of parameters characterizing the strength of motor sliding, repulsive forces generated by polymerizing MTs, and the forces arising out of interaction of MTs with kinetochores. The stability diagram helps in quantifying the relative effec...

  8. Enhanced Colloidal Stability of CeO2 Nanoparticles by Ferrous Ions: Adsorption, Redox Reaction, and Surface Precipitation.

    Science.gov (United States)

    Liu, Xuyang; Ray, Jessica R; Neil, Chelsea W; Li, Qingyun; Jun, Young-Shin

    2015-05-05

    Due to the toxicity of cerium oxide (CeO2) nanoparticles (NPs), a better understanding of the redox reaction-induced surface property changes of CeO2 NPs and their transport in natural and engineered aqueous systems is needed. This study investigates the impact of redox reactions with ferrous ions (Fe2+) on the colloidal stability of CeO2 NPs. We demonstrated that under anaerobic conditions, suspended CeO2 NPs in a 3 mM FeCl2 solution at pH 4.8 were much more stable against sedimentation than those in the absence of Fe2+. Redox reactions between CeO2 NPs and Fe2+ lead to the formation of 6-line ferrihydrite on the CeO2 surfaces, which enhanced the colloidal stability by increasing the zeta potential and hydrophilicity of CeO2 NPs. These redox reactions can affect the toxicity of CeO2 NPs by increasing cerium dissolution, and by creating new Fe(III) (hydr)oxide reactive surface layers. Thus, these findings have significant implications for elucidating the phase transformation and transport of redox reactive NPs in the environment.

  9. Noncovalent Surface Locking of Mesoporous Silica Nanoparticles for Exceptionally High Hydrophobic Drug Loading and Enhanced Colloidal Stability.

    Science.gov (United States)

    Palanikumar, L; Kim, Ho Young; Oh, Joon Yong; Thomas, Ajesh P; Choi, Eun Seong; Jeena, M T; Joo, Sang Hoon; Ryu, Ja-Hyoung

    2015-09-14

    Advances in water-insoluble drug delivery systems are limited by selective delivery, loading capacity, and colloidal and encapsulation stability. We have developed a simple and robust hydrophobic-drug delivery platform with different types of hydrophobic chemotherapeutic agents using a noncovalent gatekeeper's technique with mesoporous silica nanoparticles (MSNs). The unmodified pores offer a large volume of drug loading capacity, and the loaded drug is stably encapsulated until it enters the cancer cells owing to the noncovalently bound polymer gatekeeper. In the presence of polymer gatekeepers, the drug-loaded mesoporous silica nanoparticles showed enhanced colloidal stability. The simplicity of drug encapsulation allows any combination of small chemotherapeutics to be coencapsulated and thus produce synergetic therapeutic effects. The disulfide moiety facilitates decoration of the nanoparticles with cysteine containing ligands through thiol-disulfide chemistry under mild conditions. To show the versatility of drug targeting to cancer cells, we decorated the surface of the shell-cross-linked nanoparticles with two types of peptide ligands, SP94 and RGD. The nanocarriers reported here can release encapsulated drugs inside the reducing microenvironment of cancer cells via degradation of the polymer shell, leading to cell death.

  10. Poly(ethylene imine)-modified graphene oxide with improved colloidal stability and its adsorption of methyl orange.

    Science.gov (United States)

    Liu, Hongxi; Wu, Ting; Wu, Zhimin; Zhang, Yong; Xuan, Keqin; Zhang, Jinglin; Tan, Shaozao

    2014-01-01

    Graphene oxide (GO) was chemically modified with poly(ethylene imine) (PEI) to improve its colloidal stability and was investigated as a potential adsorbent for the removal of methyl orange (MO). The synthesis of PEI-GO was verified with a Fourier transform infrared spectrometer and thermogravimetric analysis. A series of adsorption experiments were carried out to investigate the adsorption capacity of PEI-GO. Adsorption kinetics and thermodynamics studies were performed, and the thermodynamic parameters were calculated. The results showed that PEI could improve the colloidal stability of GO in aqueous solution, and the obtained PEI-GO showed a macroscopically homogeneous dispersion after more than three months. After standing for 90 days, the Brunauer-Emmett-Teller specific surface area of GO decreased from 353 to 214 m2·g(-1), while that of PEI-GO remained almost unchanged (from 432 to 413 m2·g(-1)). The PEI-GO exhibited significantly faster kinetic and higher adsorption capacity for MO than GO. Moreover, PEI-GO had a good adsorption capacity in the acidic range, and the highest adsorption of MO occurred at pH=6.0. The adsorption of MO on PEI-GO was an endothermic, spontaneous and physisorption process.

  11. Maceration enzymes and mannoproteins: a possible strategy to increase colloidal stability and color extraction in red wines.

    Science.gov (United States)

    Guadalupe, Zenaida; Palacios, Antonio; Ayestaran, Belén

    2007-06-13

    Different strategies were adopted to achieve increases in color stability in Tempranillo wines: (i) addition of maceration enzymes directly to the must, (ii) addition of commercial mannoproteins to the must, and (iii) inoculation of must with yeast overexpressed of mannoproteins. The addition of enzymes favored color extraction, and the wines obtained presented higher values of wine color, color intensity, bisulfite-stable color, and visually enhanced color intensity. The enzyme hydrolytic activity produced an increase in the acid polysaccharide content and polyphenol index and yielded to wines with more astringency, tannin, and length. Added mannoproteins had clearer effects on the analyzed parameters than yeast. Contrary to what may be thought, mannoproteins did not maintain the extracted polyphenols in colloidal dispersion and neither ensured color stability. These compounds clearly modified the gustative structure of the wines, enhancing the sweetness and roundness.

  12. Colloidal quantum-dot-based silica gel glass: two-photon absorption, emission, and quenching mechanism.

    Science.gov (United States)

    Li, Jingzhou; Dong, Hongxing; Zhang, Saifeng; Ma, Yunfei; Wang, Jun; Zhang, Long

    2016-09-28

    Two-photon (TP) three-dimensional solid matrices have potential applications in high density optical data reading and storage, infrared-pumped visible displays, lasers, etc. Such technologies will benefit greatly from the advantageous properties of TP materials including tunable emission wavelength, photostability, and simple chemical processing. Here, this ideal TP solid is made possible by using a facile sol-gel process to engineer colloid quantum dots into silica gel glass. Characterization using an open-aperture Z-scan technique shows that the solid matrices exhibited significant TP optical properties with a TP absorption coefficient of (9.41 ± 0.39) × 10(-2) cm GW(-1) and a third-order nonlinear figure of merit of (7.30 ± 0.30) × 10(-14) esu cm. In addition, the dependence of the TP properties on high-temperature thermal treatment is studied in detail to obtain a clear insight for practical applications. The results illustrate that the sample can maintain stable TP performance below the synthesis temperature of the CdTe/CdS colloidal quantum dots. Furthermore, the mechanisms for thermal quenching of photoluminescence under different temperature regimes are clarified as a function of the composition.

  13. Dynamical density functional theory for molecular and colloidal fluids: a microscopic approach to fluid mechanics.

    Science.gov (United States)

    Archer, A J

    2009-01-07

    In recent years, a number of dynamical density functional theories (DDFTs) have been developed for describing the dynamics of the one-body density of both colloidal and atomic fluids. In the colloidal case, the particles are assumed to have stochastic equations of motion and theories exist for both the case when the particle motion is overdamped and also in the regime where inertial effects are relevant. In this paper, we extend the theory and explore the connections between the microscopic DDFT and the equations of motion from continuum fluid mechanics. In particular, starting from the Kramers equation, which governs the dynamics of the phase space probability distribution function for the system, we show that one may obtain an approximate DDFT that is a generalization of the Euler equation. This DDFT is capable of describing the dynamics of the fluid density profile down to the scale of the individual particles. As with previous DDFTs, the dynamical equations require as input the Helmholtz free energy functional from equilibrium density functional theory (DFT). For an equilibrium system, the theory predicts the same fluid one-body density profile as one would obtain from DFT. Making further approximations, we show that the theory may be used to obtain the mode coupling theory that is widely used for describing the transition from a liquid to a glassy state.

  14. The breakup mechanism of biomolecular and colloidal aggregates in a shear flow

    Science.gov (United States)

    Ó Conchúir, Breanndán; Zaccone, Alessio

    2014-03-01

    The theory of self-assembly of colloidal particles in shear flow is incomplete. Previous analytical approaches have failed to capture the microscopic interplay between diffusion, shear and intermolecular interactions which controls the aggregates fate in shear. In this work we analytically solved the drift-diffusion equation for the breakup rate of a dimer in flow. Then applying rigidity percolation theory, we found that the lifetime of a generic cluster formed under shear is controlled by the typical lifetime of a single bond in its interior, which in turn depends on the efficiency of the stress transmitted from other bonds in the cluster. We showed that aggregate breakup is a thermally-activated process where the activation energy is controlled by the interplay between intermolecular forces and the shear drift, and where structural parameters determine whether cluster fragmentation or surface erosion prevails. In our latest work, we analyzed floppy modes and nonaffine deformations to derive a lower bound on the fractal dimension df below which aggregates are mechanically unstable, ie. for large aggregates df ~= 2.4. This theoretical framework is in quantitative agreement with experiments and can be used for population balance modeling of colloidal and protein aggregation.

  15. Studies on the antimicrobial properties of colloidal silver nanoparticles stabilized by bovine serum albumin.

    Science.gov (United States)

    Mathew, Thomas V; Kuriakose, Sunny

    2013-01-01

    Colloidal silver nanoparticles were synthesised using sol-gel method and these nanoparticles were stabilised by encapsulated into the scaffolds of bovine serum albumin. Silver nanoparticles and encapsulated products were characterised by FTIR, NMR, XRD, TG, SEM and TEM analyses. Silver nanoparticle encapsulated bovine serum albumin showed highly potent antibacterial activity towards the bacterial strains such as Staphylococcus aureus, Serratia marcescens, Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae.

  16. Pu Sorption, Desorption and Intrinsic Colloid Stability under Granitic Chemical Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Pihong [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Zavarin, Mavrik [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Dai, Zurong [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kersting, Annie B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2014-09-04

    This progress report (M4FT-14LL0807031) describes research conducted at LLNL as part of the Crystalline Repository effort within the UFD program. Part I describes the dissolution kinetics of intrinsic Pu colloids synthesized in an alkaline solution. Part II describes the morphology and dissolution characteristics of various forms of Pu oxides prepared over a range of solution and temperature conditions. Proposed FY15 activities are identified.

  17. 生物法制备纳米银溶胶的稳定性%Stability of Colloidal Silver Nanoparticles Prepared by Bioreduction

    Institute of Scientific and Technical Information of China (English)

    孙道华; 李清彪; 何宁; 黄加乐; 王惠璇

    2011-01-01

    利用生物还原法制备纳米银溶胶,借助于UV-Vis表征技术对其热稳定性和化学稳定性进行考察.结果表明:生物法制备的纳米银溶胶在100℃下加热6 h,UV-Vis谱图未发生明显变化;H+和具有高价阳离子的电解质对其稳定性的影响明显;OH-对银溶胶的稳定性影响相对较弱.生物法制备的纳米银溶胶在热稳定性、化学稳定性方面均略优于柠檬酸三钠法制得的银溶胶.%The thermal and chemical statoilities of the colloid silver nanoparticles prepared by bioreduction were investigated in virtue of UV-Vis spectrometer.The results indicate that UV-Vis spectra of silver colloid prepared by bioreduction have not significant change after heat treatment at 100 ℃ for 6 h.Hydrogen ion and the electrolyte with multivalent cation markedly influence stabilities of the silver colloid, while hydroxide anion has a weak influence on its stability.Thermal and chemical stabilities of the silver colloid prepared by bioreduction are superior to that of the silver colloid prepared by the sodium citrate reduction method.

  18. Mechanical feedback stabilizes budding yeast morphogenesis

    Science.gov (United States)

    Banavar, Samhita; Trogdon, Michael; Petzold, Linda; Campas, Otger

    Walled cells have the ability to remodel their shape while sustaining an internal turgor pressure that can reach values up to 10 atmospheres. This requires a tight and simultaneous regulation of cell wall assembly and mechanochemistry, but the underlying mechanisms by which this is achieved remain unclear. Using the growth of mating projections in budding yeast (S. cerevisiae) as a motivating example, we have developed a theoretical description that couples the mechanics of cell wall expansion and assembly via a mechanical feedback. In the absence of a mechanical feedback, cell morphogenesis is inherently unstable. The presence of a mechanical feedback stabilizes changes in cell shape and growth, and provides a mechanism to prevent cell lysis in a wide range of conditions. We solve for the dynamics of the system and obtain the different dynamical regimes. In particular, we show that several parameters affect the stability of growth, including the strength of mechanical feedback in the system. Finally, we compare our results to existing experimental data.

  19. Understanding the stabilization of liquid-phase-exfoliated graphene in polar solvents: molecular dynamics simulations and kinetic theory of colloid aggregation.

    Science.gov (United States)

    Shih, Chih-Jen; Lin, Shangchao; Strano, Michael S; Blankschtein, Daniel

    2010-10-20

    Understanding the solution-phase dispersion of pristine, unfunctionalized graphene is important for the production of conducting inks and top-down approaches to electronics. This process can also be used as a higher-quality alternative to chemical vapor deposition. We have developed a theoretical framework that utilizes molecular dynamics simulations and the kinetic theory of colloid aggregation to elucidate the mechanism of stabilization of liquid-phase-exfoliated graphene sheets in N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), and water. By calculating the potential of mean force between two solvated graphene sheets using molecular dynamics (MD) simulations, we have found that the dominant barrier hindering the aggregation of graphene is the last layer of confined solvent molecules between the graphene sheets, which results from the strong affinity of the solvent molecules for graphene. The origin of the energy barrier responsible for repelling the sheets is the steric repulsions between solvent molecules and graphene before the desorption of the confined single layer of solvent. We have formulated a kinetic theory of colloid aggregation to model the aggregation of graphene sheets in the liquid phase in order to predict the stability using the potential of mean force. With only one adjustable parameter, the average collision area, which can be estimated from experimental data, our theory can describe the experimentally observed degradation of the single-layer graphene fraction in NMP. We have used these results to rank the potential solvents according to their ability to disperse pristine, unfunctionalized graphene as follows: NMP ≈ DMSO > DMF > GBL > H(2)O. This is consistent with the widespread use of the first three solvents for this purpose.

  20. The application of biofluid mechanics boundary effects on phoretic motions of colloidal spheres

    CERN Document Server

    Chen, Po-Yuan

    2014-01-01

    "The Application of Biofluid Mechanics: Boundary Effects on Phoretic Motions of Colloidal Spheres" focuses on the phoretic motion behavior of various micron- to nanometer-size particles. The content of this book is divided into two parts: one on the concentration gradient-driven diffusiophoresis and osmophoresis, and one on thermocapillary motion and thermophoretic motion driven by temperature gradient. Diffusiophoresis and osmophoresis are mainly used in biomedical engineering applications, such as drug delivery, purification, and the description of the behavior of the immune system; thermocapillary motion and thermophoretic motion are applied in the field of semiconductors, as well as in suspended impurities removal. The book also provides a variety of computer programming source codes compiled using Fortran for researchers' future applications. This book is intended for chemical engineers, biomedical engineers and scientists, biophysicists, and fundamental chemotaxis researchers. Dr. Po-Yuan Chen is an Ass...

  1. ACTH Action on Messenger RNA Stability Mechanisms

    Science.gov (United States)

    Desroches-Castan, Agnès; Feige, Jean-Jacques; Cherradi, Nadia

    2017-01-01

    The regulation of mRNA stability has emerged as a critical control step in dynamic gene expression. This process occurs in response to modifications of the cellular environment, including hormonal variations, and regulates the expression of subsets of proteins whose levels need to be rapidly adjusted. Modulation of messenger RNA stability is usually mediated by stabilizing or destabilizing RNA-binding proteins (RNA-BP) that bind to the 3′-untranslated region regulatory motifs, such as AU-rich elements (AREs). Destabilizing ARE-binding proteins enhance the decay of their target transcripts by recruiting the mRNA decay machineries. Failure of such mechanisms, in particular misexpression of RNA-BP, has been linked to several human diseases. In the adrenal cortex, the expression and activity of mRNA stability regulatory proteins are still understudied. However, ACTH- or cAMP-elicited changes in the expression/phosphorylation status of the major mRNA-destabilizing protein TIS11b/BRF1 or in the subcellular localization of the stabilizing protein Human antigen R have been reported. They suggest that this level of regulation of gene expression is also important in endocrinology.

  2. Improvement of kinetics, yield, and colloidal stability of biogenic gold nanoparticles using living cells of Euglena gracilis microalga

    Science.gov (United States)

    Dahoumane, Si Amar; Yéprémian, Claude; Djédiat, Chakib; Couté, Alain; Fiévet, Fernand; Coradin, Thibaud; Brayner, Roberta

    2016-03-01

    Recent years have witnessed a boom in the biosynthesis of a large variety of nanomaterials using different biological resources among which algae-based entities have been gaining much more attention within the community of material scientists worldwide. In our previously published findings, we explored some factors that governed the biofabrication of gold nanoparticles using living cultures of microalgae, such as the utilized microalgal genera, the phylum they belong to, and the impact of tetrachloroauric acid concentrations on the ability of these strains to perform the biosynthesis of gold nanoparticles once in contact with these cations. As a follow-up, we present in this paper an improvement of the features of bioproduced gold colloids using living cells of Euglena gracilis microalga when this species is grown under either mixotrophic or autotrophic conditions, i.e., exposed to light and grown in an organic carbon-enriched culture medium versus under autotrophic conditions. As an outcome to this alteration, the growth rate of this photosynthetic microorganism is multiplied 7-8 times when grown under mixotrophic conditions compared to autotrophic ones. Therefore, the yield, the kinetics, and the colloidal stability of the biosynthesized gold nanoparticles are dramatically enhanced. Moreover, the shape and the size of the as-produced nano-objects via this biological method are affected. In addition to round-shaped gold nanoparticles, particular shapes, such as triangles and hexagons, appear. These findings add up to the amassed knowledge toward the design of photobioreactors for the scalable and sustainable production of interesting nanomaterials.

  3. Geared Topological Metamaterials with Tunable Mechanical Stability

    Science.gov (United States)

    Meeussen, Anne S.; Paulose, Jayson; Vitelli, Vincenzo

    2016-10-01

    The classification of materials into insulators and conductors has been shaken up by the discovery of topological insulators that conduct robustly at the edge but not in the bulk. In mechanics, designating a material as insulating or conducting amounts to asking if it is rigid or floppy. Although mechanical structures that display topological floppy modes have been proposed, they are all vulnerable to global collapse. Here, we design and build mechanical metamaterials that are stable and yet capable of harboring protected edge and bulk modes, analogous to those in electronic topological insulators and Weyl semimetals. To do so, we exploit gear assemblies that, unlike point masses connected by springs, incorporate both translational and rotational degrees of freedom. Global structural stability is achieved by eliminating geometrical frustration of collective gear rotations extending through the assembly. The topological robustness of the mechanical modes makes them appealing across scales from engineered macrostructures to networks of toothed microrotors of potential use in micromachines.

  4. Geared Topological Metamaterials with Tunable Mechanical Stability

    Directory of Open Access Journals (Sweden)

    Anne S. Meeussen

    2016-11-01

    Full Text Available The classification of materials into insulators and conductors has been shaken up by the discovery of topological insulators that conduct robustly at the edge but not in the bulk. In mechanics, designating a material as insulating or conducting amounts to asking if it is rigid or floppy. Although mechanical structures that display topological floppy modes have been proposed, they are all vulnerable to global collapse. Here, we design and build mechanical metamaterials that are stable and yet capable of harboring protected edge and bulk modes, analogous to those in electronic topological insulators and Weyl semimetals. To do so, we exploit gear assemblies that, unlike point masses connected by springs, incorporate both translational and rotational degrees of freedom. Global structural stability is achieved by eliminating geometrical frustration of collective gear rotations extending through the assembly. The topological robustness of the mechanical modes makes them appealing across scales from engineered macrostructures to networks of toothed microrotors of potential use in micromachines.

  5. Improved magnetic induction heating of nanoferrites for hyperthermia applications: Correlation with colloidal stability and magneto-structural properties

    Energy Technology Data Exchange (ETDEWEB)

    Khot, V.M., E-mail: wish_khot@yahoo.co.in [Center for Interdisciplinary Research, D. Y. Patil University, Kolhapur 416006 (India); Salunkhe, A.B. [Advanced Materials Laboratory, Department of Physics, Savitribai Phule University of Pune (India); Ruso, J.M. [Soft Matter and Molecular Biophysics Group, Applied Physics Department, University of Santiago de Compostela, Santiago de Compostela (Spain); Pawar, S.H. [Center for Interdisciplinary Research, D. Y. Patil University, Kolhapur 416006 (India)

    2015-06-15

    Nanoferrites with compositions Mn{sub 0.4}Zn{sub 0.6}Fe{sub 2}O{sub 4}, Co{sub 0.4}Zn{sub 0.6}Fe{sub 2}O{sub 4}, Ni{sub 0.4}Zn{sub 0.6}Fe{sub 2}O{sub 4} (MZF, CZF and NZF respectively) coated with polyethylene glycol (PEG) were prepared in a single step. These nanoparticles are highly water dispersible with zeta potential values between 14 and 21 mV. Magnetic induction heating characteristics of these NPs have been studied as a function of magnetic field amplitude from 6.7 to 26.7 kA m{sup −1} (at fixed frequency 265 kHz) and concentration of nanoparticles. Notable enhancement in specific absorption rate (334.5 W g{sup −1}) by CZF nanoparticles has been observed. This enhanced induction heating properties have been studied and correlated with colloidal stability and magnetostructural properties such as tuned magnetic anisotropy arising from zinc substitution. Cytotoxicity of synthesized mixed ferrites has been evaluated in vitro on HeLa cell lines using MTT assay to explore their use as heating agents in magnetic hyperthermia. - Highlights: • Magnetic nanoferrites (sizes 8–12 nm) with improved specific absorption rate (334.5 W g{sup −1}) at lowest particle concentration have been prepared • The results have been explained by correlating colloidal stability and magnetostructural properties such as magnetocrystalline anisotropy. • It has been shown that substitution of zinc tunes anisotropy of cobalt iron oxide within the value optimized previously in achieving high throughput in magnetic induction heating. • In vitro cytotoxicity proves nanoparticles are non-toxic suggesting their use as a potential heating agent in hyperthermia therapy.

  6. Electrophoresis and stability of nano-colloids: history, theory and experimental examples.

    Science.gov (United States)

    Felix, C; Yaroshchuk, A; Pasupathi, S; Pollet, B G; Bondarenko, M P; Kovalchuk, V I; Zholkovskiy, E K

    2014-09-01

    The paper contains an extended historical overview of research activities focused on determining interfacial potential and charge of dispersed particles from electrophoretic and coagulation dynamic measurements. Particular attention is paid to nano-suspensions for which application of Standard Electrokinetic Model (SEM) to analysis of experimental data encounters difficulties, especially, when the solutions contain more than two ions, the particle charge depends on the solution composition and zeta-potentials are high. Detailed statements of Standard Electrokinetic and DLVO Models are given in the forms that are capable of addressing electrophoresis and interaction of particles for arbitrary ratios of the particle to Debye radius, interfacial potentials and electrolyte compositions. The experimental part of the study consists of two groups of measurements conducted for Pt/C nano-suspensions, namely, the electrophoretic and coagulation dynamic studies, with various electrolyte compositions. The obtained experimental data are processed by using numerical algorithms based on the formulated models for obtaining interfacial potential and charge. While analyzing the dependencies of interfacial potential and charge on the electrolyte compositions, conclusions are made regarding the mechanisms of charge formation. It is established that the behavior of system stability is in a qualitative agreement with the results computed from the electrophoretic data. The verification of quantitative applicability of the employed models is conducted by calculating the Hamaker constant from experimental data. It is proposed how to explain the observed variations of predicted Hamaker constant and its unusually high value.

  7. The role of a microscopic colloidally stabilized phase in solubilizing oligoamine-condensed DNA complexes.

    Science.gov (United States)

    Trubetskoy, Vladimir S; Wolff, Jon A; Budker, Vladimir G

    2003-02-01

    DNA complexes of spermine and spermidine become resolubilized at very high concentrations of the oligoamine. It has been postulated that high oligoamine concentrations shift the DNA from the globule back to the coil phase. The present study indicates that DNA resolubilization at high concentrations of spermine and spermidine is explained by formation of small particles of condensed DNA that cannot be precipitated by centrifugation. The fact that DNA stays condensed during resolubilization was confirmed using a relatively new condensation assay and three independent microscopic techniques. A considerable portion of DNA was found to be in particles with diameter <100 nm. Formation of such small particles is likely to be caused by colloidal forces. The ability to form small, condensed DNA particles in solutions that contain high concentrations of oligocation should aid in the design of synthetic DNA vectors for gene transfer and gene therapy and in the handling of DNA for diagnostic studies.

  8. Colloid-Associated Radionuclide Concentration Limits: ANL

    Energy Technology Data Exchange (ETDEWEB)

    C. Mertz

    2000-12-21

    The purpose and scope of this report is to describe the analysis of available colloidal data from waste form corrosion tests at Argonne National Laboratory (ANL) to extract characteristics of these colloids that can be used in modeling their contribution to the source term for sparingly soluble radioelements (e.g., Pu). Specifically, the focus is on developing a useful description of the following waste form colloid characteristics: (1) composition, (2) size distribution, and (3) quantification of the rate of waste form colloid generation. The composition and size distribution information are intended to support analysis of the potential transport of the sparingly soluble radionuclides associated with the waste form colloids. The rate of colloid generation is intended to support analysis of the waste form colloid-associated radionuclide concentrations. In addressing the above characteristics, available data are interpreted to address mechanisms controlling colloid formation and stability. This report was developed in accordance with the ''Technical Work Plan for Waste Form Degradation Process Model Report for SR'' (CRWMS M&O 2000). Because the end objective is to support the source term modeling we have organized the conclusions into two categories: (1) data analysis conclusions and (2) recommendations for colloid source term modeling. The second category is included to facilitate use of the conclusions from the data analysis in the abstraction of a colloid source term model. The data analyses and conclusions that are presented in this report are based on small-scale laboratory tests conducted on a limited number of waste glass compositions and spent fuel types.

  9. PEG-stabilized core-shell nanoparticles: impact of linear versus dendritic polymer shell architecture on colloidal properties and the reversibility of temperature-induced aggregation.

    Science.gov (United States)

    Gillich, Torben; Acikgöz, Canet; Isa, Lucio; Schlüter, A Dieter; Spencer, Nicholas D; Textor, Marcus

    2013-01-22

    Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely used experimentally and also clinically tested in diverse areas of biology and medicine. Applications include magnetic resonance imaging, cell sorting, drug delivery, and hyperthermia. Physicochemical surface properties are particularly relevant in the context of achieving high colloidal nanoparticle (NP) stability and preventing agglomeration (particularly challenging in biological fluids), increasing blood circulation time, and possibly targeting specific cells or tissues through the presentation of bioligands. Traditionally, NP surfaces are sterically stabilized with hydrophilic polymeric matrices, such as dextran or linear poly(ethylene glycol) brushes. While dendrimers have found applications as drug carriers, dispersants with dendritic ("dendrons") or hyperbranched structures have been comparatively neglected despite their unique properties, such as a precisely defined molecular structure and the ability to present biofunctionalities at high density at the NP periphery. This work covers the synthesis of SPIONs and their stabilization based on poly(ethylene glycol) (PEG) and oligo(ethylene glycol) (OEG) chemistry and compares the physicochemical properties of NPs stabilized with linear and dendritic macromolecules of comparable molecular weight. The results highlight the impact of the polymeric interface architecture on solubility, colloidal stability, hydrodynamic radius, and thermoresponsive behavior. Dendron-stabilized NPs were found to provide excellent colloidal stability, despite a smaller hydrodynamic radius and lower degree of soft shell hydration compared to linear PEG analogues. Moreover, for the same grafting density and molecular weight of the stabilizers, OEG dendron-stabilized NPs show a reversible temperature-induced aggregation behavior, in contrast to the essentially irreversible aggregation and sedimentation observed for the linear PEG analogues. This new class of

  10. Transport coefficients and mechanical response in hard-disk colloidal suspensions

    Science.gov (United States)

    Zhang, Bo-Kai; Li, Jian; Chen, Kang; Tian, Wen-De; Ma, Yu-Qiang

    2016-11-01

    We investigate the transport properties and mechanical response of glassy hard disks using nonlinear Langevin equation theory. We derive expressions for the elastic shear modulus and viscosity in two dimensions on the basis of thermal-activated barrier-hopping dynamics and mechanically accelerated motion. Dense hard disks exhibit phenomena such as softening elasticity, shear-thinning of viscosity, and yielding upon deformation, which are qualitatively similar to dense hard-sphere colloidal suspensions in three dimensions. These phenomena can be ascribed to stress-induced “landscape tilting”. Quantitative comparisons of these phenomena between hard disks and hard spheres are presented. Interestingly, we find that the density dependence of yield stress in hard disks is much more significant than in hard spheres. Our work provides a foundation for further generalizing the nonlinear Langevin equation theory to address slow dynamics and rheological behavior in binary or polydisperse mixtures of hard or soft disks. Project supported by the National Basic Research Program of China (Grant No. 2012CB821500) and the National Natural Science Foundation of China (Grant Nos. 21374073 and, 21574096).

  11. Stabilization and synchronization of networked mechanical systems

    Science.gov (United States)

    Nair, Sujit S.

    The main theme of this thesis is coordination and stabilization of a network of mechanical systems or rigid bodies to achieve synchronized behaviour. The idea is to use controls derived from potentials to couple the systems such that the closed-loop system is also a mechanical system with a Lagrangian structure. This permits the closed-loop Hamiltonian to be used as a Lyapunov function for stability analysis. It is a big challenge to develop a provable, systematic methodology to control and coordinate a network of systems to perform a given task. The control law should be robust enough to handle environment uncertainties, avoid obstacles and collisions and keep the system formation going. The fact that these systems may even have unstable dynamics makes the problem even more interesting and exciting both from a theoretical and applied point of view. This work investigates the coordination problem when each individual system has its own (maybe unstable) dynamics; this distinguishes this work from many other recent works on coordination control where the individual system dynamics are assumed to be single/double integrators. We build coordination techniques for three kinds of systems. The first one consists of underactuated Lagrangian systems with Abelian symmetry groups lacking gyroscopic forces. Asymptotic stabilization is proved for two cases, one which yields convergence to synchronized motion restricted to a constant momentum surface and one in which the system converges asymptotically to a relative equilibrium. Next we consider rigid body systems where the configuration space of each individual body is the non Abelian Lie group SO(3) or SE(3). In the SO(3) case, the asymptotically stabilized solution corresponds to each rigid body rotating about its unstable middle axis and all the bodies synchronized and pointing in a particular direction in inertial space. In the SE(3) case, the asymptotically stabilized solution corresponds to each rigid body rotating about

  12. In situ growth of hollow gold-silver nanoshells within porous silica offers tunable plasmonic extinctions and enhanced colloidal stability.

    Science.gov (United States)

    Li, Chien-Hung; Jamison, Andrew C; Rittikulsittichai, Supparesk; Lee, Tai-Chou; Lee, T Randall

    2014-11-26

    Porous silica-coated hollow gold-silver nanoshells were successfully synthesized utilizing a procedure where the porous silica shell was produced prior to the transformation of the metallic core, providing enhanced control over the structure/composition of the bimetallic hollow core. By varying the reaction time and the precise amount of gold salt solution added to a porous silica-coated silver-core template solution, composite nanoparticles were tailored to reveal a readily tunable surface plasmon resonance that could be centered across the visible and near-IR spectral regions (∼445-800 nm). Characterization by X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy revealed that the synthetic methodology afforded particles having uniform composition, size, and shape. The optical properties were evaluated by absorption/extinction spectroscopy. The stability of colloidal solutions of our composite nanoparticles as a function of pH was also investigated, revealing that the nanoshells remain intact over a wide range of conditions (i.e., pH 2-10). The facile tunability, enhanced stability, and relatively small diameter of these composite particles (∼110 nm) makes them promising candidates for use in tumor ablation or as photothermal drug-delivery agents.

  13. Adsorption of polyelectrolyte on the surface of ZnO nanoparticles and the stability of colloidal dispersions

    Institute of Scientific and Technical Information of China (English)

    LIUFU Shengcong; XIAO Hanning; LI Yuping

    2005-01-01

    The present study focuses on the adsorption of a polyelectrolyte, the component of which is a polymer of maleic anhydride sodium salt, on the surface of nanometric zinc oxide particles and the colloidal stability of aqueous dispersions. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the polyelectrolyte-ZnO system. The adsorption isotherms showed the influences of polyelectrolyte concentration, pH and ionic strength on the adsorption. With the increase of pH the saturated adsorbed amount decreased, while the thickness of adsorption layer increased. The saturated adsorbed amount increased with increasing salt concentration, and decreased with further increasing salt concentration. It should be noted that in the presence of a CaCl2 solution the adsorbed amount and the adsorption layer thickness were greater than those in the NaCl solution of the same concentration. The change of the absorbance of zinc oxide dispersions showed that the absorbance decreased slowly at high pH. There was a maximum point for the absorbance of the zinc oxide dispersions in the presence of various polyelectrolyte concentrations. The change of dispersion stability resulted from the change of macromolecular chains conformation at the interface.

  14. Colloidal suspensions hydrodynamic retention mechanisms in model porous media; Mecanismes de retention hydrodynamique de suspensions colloidales en milieux poreux modeles

    Energy Technology Data Exchange (ETDEWEB)

    Salehi, N.

    1996-04-19

    This study deals with the retention mechanisms of colloidal particles in porous media flows, and the subsequent reduction in permeability in the case of stable and non adsorbing colloids. It combines experimental results and modelling. This study has been realised with stable dispersion of monodispersed carboxylate polystyrene latexes negatively charged injected through negatively charged polycarbonate membranes having mono-sized cylindrical pores. The mean particle diameter is smaller than the mean pore diameter. Both batch and flow experiments in Nuclepore membranes have been done. The results of batch experiments have proved no adsorption of the colloidal latex particles on the surface of the Nuclepore membranes without flow at low salinity. In flow experiments at low particle concentration, only deposition on the upstream side of the membrane have been induced by hydrodynamic forces even for non adsorbing particles without creating any permeability reduction. The retention levels are zero at low and high Peclet numbers with a maximum at intermediate values. Partial plugging was observed at higher colloid concentration even at low salinity without any upstream surface deposition. The modelling of plugging processes is achieved by considering the particle concentration, fluid rate and ratio between the mean pore diameter and the mean particle diameter. This study can be particularly useful in the fields of water treatment and of restoration of lands following radioactive contamination. (author). 96 refs., 99 figs., 29 tabs.

  15. Colloidal photonic glass for electro-optic display stabilized with potassium persulfate (KPS) in polar solvent

    Science.gov (United States)

    Lee, Hye-Young; Kim, Young-Seok; Yi, Gi-Ra

    2016-04-01

    We introduced carbon-shell with potassium persulfate structure to modify the repulsive force between particles and minimize scattered light. The reflected structural color varied from blue to red and showed high color purity with high cycle stability.

  16. The Structure-Function Relationship of Polymeric Sorbents for Colloid Stabilization of Beer

    OpenAIRE

    Basarova, Gabriela

    1990-01-01

    This review considers the research relating to the formation of non-biological haze in beer. The basic information regarding mutual interactions of haze-causing substances with precipitating, enzymatic, and adsorptive stabilizers of beer is discu ssed. The main haze-causing compounds in beer are polypeptides and polyphenols. To reduce the levels of these compounds in beer, adsorptive stabilizing agents are usually used during filt ration. Electron microscopy and methods measuring the surface ...

  17. Green synthesis of Au nanoparticles using potato extract: stability and growth mechanism

    Science.gov (United States)

    Castillo-López, D. N.; Pal, U.

    2014-08-01

    We report on the synthesis of spherical, well-dispersed colloidal gold nanoparticles of 17.5-23.5 nm average sizes in water using potato extract (PE) both as reducing and stabilizing agent. The effects of PE content and the pH value of the reaction mixture have been studied. Formation and growth dynamics of the Au nanoparticles in the colloids were studied using transmission electron microscopy and UV-Vis optical absorption spectroscopy techniques. While the reductor content and, hence, the nucleation and growth rates of the nanoparticles could be controlled by controlling the PE content in the reaction solution, the stability of the nanoparticles depended strongly on the pH of the reaction mixture. The mechanisms of Au ion reduction and stabilization of Au nanoparticles by potato starch have been discussed. The use of common natural solvent like water and biological reductor like PE in our synthesis process opens up the possibility of synthesizing Au nanoparticles in fully green (environmental friendly) way, and the Au nanoparticles produced in such way should have good biocompatibility.

  18. Structure, stability, and formation pathways of colloidal gels in systems with short-range attraction and long-range repulsion.

    Science.gov (United States)

    van Schooneveld, Matti M; de Villeneuve, Volkert W A; Dullens, Roel P A; Aarts, Dirk G A L; Leunissen, Mirjam E; Kegel, Willem K

    2009-04-09

    We study colloidal gels formed upon centrifugation of dilute suspensions of spherical colloids (radius 446 nm) that interact through a long-range electrostatic repulsion (Debye length approximately 850 nm) and a short-range depletion attraction (approximately 12.5 nm), by means of confocal scanning laser microscopy (CSLM). In these systems, at low colloid densities, colloidal clusters are stable. Upon increasing the density by centrifugation, at different stages of cluster formation, we show that colloidal gels are formed that significantly differ in structure. While significant single-particle displacements do not occur on the hour time scale, the different gels slowly evolve within several weeks to a similar structure that is at least stable for over a year. Furthermore, while reference systems without long-range repulsion collapse into dense glassy states, the repulsive colloidal gels are able to support external stress in the form of a centrifugal field of at least 9g.

  19. Chemical, colloidal and mechanical contributions to the state of water in wood cell walls

    Science.gov (United States)

    Bertinetti, L.; Fratzl, P.; Zemb, T.

    2016-08-01

    The properties of wood depend strongly on its water content, but the physicochemical basis for the interaction of water with cell wall components is poorly understood. Due to the importance of the problem both in the context of wood technology and the biological function of swelling and dehydration for growth stresses and seed dispersal, a wealth of descriptive data has been accumulated but a microscopic theory of water-biomolecular interactions is missing. We develop here, at a primitive level, a minimal parameter-free, coarse-grained, model of wood secondary cell walls to predict water absorption, in the form of an equation of state. It includes for the first time all three—mechanical, colloidal and chemical—contributions, taking into account the cell walls microstructure. The hydration force around the elongated cellulose crystals and entropy of mixing of the matrix polymers (hemicelluloses and lignin) are the dominant contributions driving the swelling. The elastic energy needed to swell the composite is the main term opposing water uptake. Hysteresis is not predicted but water uptake versus humidity, is reproduced in a large temperature range. Within this framework, the origin of wood dissolution and different effects of wood treatments on water sorption can be understood at the molecular level.

  20. Oral Toxicity and Intestinal Transport Mechanism of Colloidal Gold Nanoparticle-Treated Red Ginseng

    Science.gov (United States)

    Bae, Song-Hwa; Yu, Jin; Go, Mi-Ran; Kim, Hyun-Jin; Hwang, Yun-Gu; Choi, Soo-Jin

    2016-01-01

    (1) Background: Application of nanotechnology or nanomaterials in agricultural food crops has attracted increasing attention with regard to improving crop production, quality, and nutrient utilization. Gold nanoparticles (Au-NPs) have been reported to enhance seed yield, germination rate, and anti-oxidant potential in food crops, raising concerns about their toxicity potential. In this study, we evaluated the oral toxicity of red ginseng exposed to colloidal Au-NPs during cultivation (G-red ginseng) in rats and their intestinal transport mechanism. (2) Methods: 14-day repeated oral administration of G-red ginseng extract to rats was performed, and body weight, hematological, serum biochemical, and histopathological values were analyzed. An in vitro model of human intestinal follicle-associated epithelium (FAE) and an intestinal epithelial monolayer system were used for intestinal transport mechanistic study. (3) Results: No remarkable oral toxicity of G-red ginseng extract in rats was found, and Au-NPs did not accumulate in any organ, although Au-NP transfer to G-red ginseng and some increased saponin levels were confirmed. Au-NPs were transcytozed by microfold (M) cells, but not by a paracellular pathway in the intestinal epithelium. (4) Conclusion: These findings suggest great potential of Au-NPs for agricultural food crops at safe levels. Further study is required to elucidate the functional effects of Au-NPs on ginseng and long-term toxicity. PMID:28335336

  1. Hydrophobically Associating Polyethylenimine for Controlling Dissolved and Colloidal Substances of Alkaline Peroxide Mechanical Pulp

    Directory of Open Access Journals (Sweden)

    Guang-lei Zhao

    2014-01-01

    Full Text Available In a paper mill’s water circuit, normal runnability of the paper machine is often disturbed due to buildup of hydrophobic dissolved and colloidal substances (DCS, such as wood pitch, white pitch, and stickies. General cationic fixing agents such as hydrophilic polymers do not always work to minimize these problems. In the present study, two kinds of novel hydrophobically associating polyethylenimine (PEI coagulants grafted by acetic anhydride and 1,2-epoxydodecane, named PEI-Ac and PEI-Ed, respectively, were synthesized to remove hydrophobic DCS. The performances of the modified PEI samples were evaluated using a model suspension containing alkaline peroxide mechanical pulp (APMP and styrene-butadiene latex. The results showed that the modified PEI was more inclined to interact with hydrophobic substances than was non-modified PEI. The relationship between DCS removal and non-modified or modified PEI content was not linear, but there was a maximum. The turbidity and particle counts of model suspensions decreased 30% and 80%, respectively, when the dosage of PEI-Ed(a was 0.025%. Compared with the 72.8% decrease in the case of non-modified PEI, cationic demand decreased by 67.7% when the PEI-Ed(a concentration was 0.2%. It was also found that PEI-Ed had a better affinity for DCS than PEI-Ac, which may be because the PEI-Ed had a long hydrophobic chain.

  2. Enhancing the stability of colloidal silver nanoparticles using polyhydroxyalkanoates (PHA) from Bacillus circulans (MTCC 8167) isolated from crude oil contaminated soil.

    Science.gov (United States)

    Phukon, Pinkee; Saikia, Jyoti Prasad; Konwar, Bolin Kumar

    2011-09-01

    Polyhydroxyalkanoate (PHA) was produced by growing Bacillus circulans (MTCC 8167) in the specific detection medium. The identification of the polymer as PHA was confirmed by fluorescence microscopy. The PHA was purified and characterized using FT-IR. The silver nanoparticles (SNP) were synthesized from AgNO3 in the dispersed colloids of PHA (0.085%) using NaBH4 (sodium borohydrate as reducing agent). The stability was tested using wave length scanning with a UV-Vis spectrophotometer and finally with transmission electron microscopy. The PHA stabilized solution was found to be stable for 30 days as against the low stability of silver nanoparticles (SNP) solution alone.

  3. Preparation of Ce-doped colloidal SiO{sub 2} composite abrasives and their chemical mechanical polishing behavior on sapphire substrates

    Energy Technology Data Exchange (ETDEWEB)

    Lei, Hong, E-mail: hong_lei2005@aliyun.com [School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418 (China); Research Center of Nano-science and Nano-technology, Shanghai University, Shanghai 200444 (China); Tong, Kaiyu; Wang, Zhanyong [School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai 201418 (China)

    2016-04-01

    Chemical mechanical polishing (CMP) has become a widely accepted global planarization technology. Abrasive is one of key elements during CMP process. In order to enhance removal rate and improve surface quality of sapphire substrate, a series of novel Ce-doped colloidal SiO{sub 2} composite abrasives were prepared by chemical co-precipitation method. The CMP performances of the Ce-doped colloidal SiO{sub 2} composite abrasives on sapphire substrate were investigated by using UNIPOL-1502 polishing equipment. The analyses on the surface of polished sapphire substrate indicate that slurries containing the Ce-doped colloidal SiO{sub 2} composite abrasives exhibit lower surface roughness, higher material removal rate than that of pure colloidal SiO{sub 2} abrasive under the same testing conditions. Furthermore, the acting mechanism of the Ce-doped colloidal silica in sapphire CMP was investigated. X-ray photoelectron spectroscopy analysis shows that solid-state chemical reactions between Ce-doped silica abrasives and sapphire surface occur during CMP process, which can promote the chemical effect in CMP and lead to the improvement of material removing rate. - Highlights: • Novel Ce-doped colloidal SiO{sub 2} composite abrasives were prepared. • The chemical mechanical polishing (CMP) performances of the composite abrasives on sapphire substrate were investigated. • Novel composite abrasives show excellent polishing characteristics comparison with pure colloidal SiO{sub 2} abrasive. • We explore and report the acting mechanism of composite abrasives to sapphire CMP.

  4. LABORATORY STUDIES ON THE STABILITY AND TRANSPORT OF INORGANIC COLLOIDS THROUGH NATURAL AQUIFER MATERIAL

    Science.gov (United States)

    The stability and transport of radio-labeled Fe2O3 particles were studied using laboratory batch and column techniques. Core material collected from shallow sand and gravel aquifer was used as the immobile column matrix material. Variables in the study included flow rate, pH, i...

  5. Colloidal Properties and Stability of Graphene Oxide Nanomaterials in the Aquatic Environment

    Science.gov (United States)

    While graphene oxide (GO) has been found to be the most toxic graphene-based nanomaterial, its environmental fate is still unexplored. In this study, the aggregation kinetics and stability of GO were investigated using time-resolved dynamic light scattering over a wide range of a...

  6. Chemical mechanical polishing of steel substrate using colloidal silica-based slurries

    Science.gov (United States)

    Jiang, Liang; He, Yongyong; Luo, Jianbin

    2015-03-01

    AISI 52100 steel has been widely used in the mechanical industry due to its excellent mechanical properties and high availability. In some cases, an ultra-smooth surface of AISI 52100 steel is needed and is even indispensable for the satisfactory performance of devices. In this paper, chemical mechanical polishing technique was employed to prepare the ultra-smooth surface of AISI 52100 steel. Colloidal silica was used as the abrasive. The effects of pH, complexing agent such as glycine, H2O2 and benzotriazole (BTA) on the polishing performance were studied. It is revealed that, with the increase of pH, the static etching rate (SER) and the material removal rate (MRR) are both gradually reduced, and the post-CMP surface roughness Ra decreases. This is attributed to the fact that compact and passive iron oxides, especially Fe(III) oxides, gradually form on the top surface. At pH 4.00, in the presence of glycine, and with the increase of the H2O2 concentration, the SER is further suppressed, and the surface roughness Ra gradually decreases; the MRR initially dramatically increases due to the fact that, with the addition of small amount of H2O2, the porous iron oxide layer with relatively low mechanical strength can be rapidly formed on the surface. Moreover, glycine intensifies the chemical dissolution by chelating iron ions, especially Fe(II) ions, and thereby the mechanical strength of the oxide layer further weakens. Then, after reaching the peak value, the MRR gradually decreases when the H2O2 concentration further increases since the compactness of the oxide layer gradually increases. With the increase of the BTA concentration, the MRR is gradually suppressed and the surface roughness Ra decreases due to the formation of Fe-BTA passivating film on the top surface. Finally, a two-step polishing process was developed. The polishing results show that, within 20 min, a rough surface of AISI 52100 steel with the Ra value of 188 nm can be polished into an ultra

  7. Influence of Temperature on the Colloidal Stability of Polymer-Coated Gold Nanoparticles in Cell Culture Media.

    Science.gov (United States)

    Zyuzin, Mikhail V; Honold, Tobias; Carregal-Romero, Susana; Kantner, Karsten; Karg, Matthias; Parak, Wolfgang J

    2016-04-06

    The temperature-dependence of the hydrodynamic diameter and colloidal stability of gold-polymer core-shell particles with temperature-sensitive (poly(N-isopropylacrylamide)) and temperature-insensitive shells (polyallylaminine hydrochloride/polystyrensulfonate, poly(isobutylene-alt-maleic anhydride)-graft-dodecyl) are investigated in various aqueous media. The data demonstrate that for all nanoparticle agglomeration, i.e., increase in effective nanoparticle size, the presence of salts or proteins in the dispersion media has to be taken into account. Poly(N-isopropylacrylamide) coated nanoparticles show a reversible temperature-dependent increase in size above the volume phase transition of the polymer shell when they are dispersed in phosphate buffered saline or in media containing protein. In contrast, the nanoparticles coated with temperature-insensitive polymers show a time-dependent increase in size in phosphate buffered saline or in medium containing protein. This is due to time-dependent agglomeration, which is particularly strong in phosphate buffered saline, and induces a time-dependent, irreversible increase in the hydrodynamic diameter of the nanoparticles. This demonstrates that one has to distinguish between temperature- and time-induced agglomerations. Since the size of nanoparticles regulates their uptake by cells, temperature-dependent uptake of thermosensitive and non-thermosensitive nanoparticles by cells lines is compared. No temperature-specific difference between both types of nanoparticles could be observed.

  8. Colloidal Plasmas : Basic physics of colloidal plasmas

    Indian Academy of Sciences (India)

    C B Dwivedi

    2000-11-01

    Colloidal plasma is a distinct class of the impure plasmas with multispecies ionic composition. The distinction lies in the phase distribution of the impurity-ion species. The ability to tailor the electrostatic interactions between these colloidal particles provides a fertile ground for scientists to investigate the fundamental aspects of the Coulomb phase transition behavior. The present contribution will review the basic physics of the charging mechanism of the colloidal particles as well as the physics of the collective normal mode behavior of the general multi-ion species plasmas. Emphasis will be laid on the clarification of the prevailing confusing ideas about distinct qualities of the various acoustic modes, which are likely to exist in colloidal plasmas as well as in normal multi-ion species plasmas. Introductory ideas about the proposed physical models for the Coulomb phase transition in colloidal plasma will also be discussed.

  9. Experimental Studies to Evaluate the Role of Colloids on the Radionuclide Migration in a Crystalline Medium

    Energy Technology Data Exchange (ETDEWEB)

    Albarran, Nairoby; Missana, Tiziana; Alonso, Ursula; Garcia-Gutierrez, Miguel; Mingarro, Manuel; Lopez, Trinidad [CIEMAT, Departamento de Medioambiente, Avenida Complutense, 22 28040 Madrid (Spain)

    2008-07-01

    In a deep geological repository (DGR) of high level radioactive waste, all the possible phenomena affecting radionuclide migration have to be studied to assess its security over time. Colloids can play an important role for contaminant transport if the following conditions are fulfilled: colloids exist in a non negligible concentration, they are mobile and stable in the environment of interest, and they are able to adsorb radionuclides irreversibly. In this study, different transport experiments where performed to improve the knowledge on the main mechanisms affecting the radionuclide migration in the presence of colloids in a crystalline medium. Firstly, colloid stability was analysed and then transport experiments in an artificial granite longitudinal fracture were carried out. Synthetic colloids of different size and bentonite clay colloids were used to evaluate the effects of colloid size, charge, and water flow rate on their mobility. Results showed that both major importance of the water flow rate on the mobility of colloids and their recovery and a higher interaction of smaller particles with the surface. Finally, the migration behaviour of Sr, and Sr adsorbed onto bentonite colloids was compared. The elution curves of Sr adsorbed onto colloid were significantly different from the ones of Sr alone, pointing out that sorption/desorption mechanisms must be taken into account to understand the radionuclide migration in the fracture in the presence of colloids. (authors)

  10. Studies of colloids and their importance for repository performance assessment

    Energy Technology Data Exchange (ETDEWEB)

    Laaksoharju, M.; Skaarman, C. [GeoPoint AB, Sollentuna (Sweden); Degueldre, C. [Geneva Univ. (Switzerland)

    1995-12-01

    The processes, parameters and data used to evaluate the potential of nuclide transport by a colloid facilitated mechanism are reviewed and discussed in this report. Both steady-state (present situation) and possible future non-steady-state hydrogeochemistry in the geosphere are covered. In the steady-state scenario, the colloid (clay, silica, iron(III)hydroxide) concentration is around 20-45 micrograms/l which is considered to be a low value. The low colloid concentration is justified by the large attachment factor to the rock which reduces the stability of the colloids in the aquifer. Both reversible and irreversible sorption processes are reviewed. In the non-steady-state scenario, changes of hydrogeochemical properties may induce larger colloid concentrations. The increase of concentration is however limited and relaxation is always observed after any change. Emphasis is placed on the glaciation-deglaciation scenario. 53 refs, 12 figs, 3 tabs.

  11. Effect of temperature on high shear-induced gelation of charge-stabilized colloids without adding electrolytes.

    Science.gov (United States)

    Wu, Hua; Tsoutsoura, Aikaterini; Lattuada, Marco; Zaccone, Alessio; Morbidelli, Massimo

    2010-02-16

    We demonstrated previously (Wu, H.; Zaccone, A.; Tsoutsoura, A.; Lattuada, M.; Morbidelli, M. Langmuir 2009, 25, 4715) that, for a colloid stabilized by charges from both polymer chain-end groups and adsorbed sulfonate surfactants, when the surfactant surface density reaches a certain critical value, the shear-induced gelation becomes unachievable at room temperature, even at an extremely large Peclet number, Pe = 4.6 x 10(4). This is due to the presence of the short-range, repulsive hydration force generated by the adsorbed surfactant. In this work, we investigate how such hydration force affects the shear-induced gelation at higher temperatures, in the range between 303 and 338 K. It is found that a colloidal system, which does not gel at room temperature in a microchannel at a fixed Pe = 3.7 x 10(4), does gel when temperature increases to a certain value. The critical initial particle volume fraction for the gelation to occur decreases as temperature increases. These results indicate that the effect of the hydration force on the gelation decreases as temperature increases. Moreover, we have observed that at the criticality only part of the primary particles is converted to the gel network and the effective particle volume fraction forming the gel network does not change significantly with temperature. The effective particle volume fraction is also independent of the surfactant surface coverage. Since the effective particle volume fraction corresponds to space filling requirement of a standing gel network, which is mainly related to the clusters structure, this result indicates that at a given shear rate the cluster structure does not change significantly with the surfactant surface coverage. On the other hand, since the cluster morphology is a strong function of the shear rate, we have observed that when the Peclet number is lowered from Pe = 3.7 x 10(4) to 1.7 x 10(4), the effective particle volume fraction reduces from 0.19 to 0.12 at 313 K.

  12. UZ Colloid Transport Model

    Energy Technology Data Exchange (ETDEWEB)

    M. McGraw

    2000-04-13

    The UZ Colloid Transport model development plan states that the objective of this Analysis/Model Report (AMR) is to document the development of a model for simulating unsaturated colloid transport. This objective includes the following: (1) use of a process level model to evaluate the potential mechanisms for colloid transport at Yucca Mountain; (2) Provide ranges of parameters for significant colloid transport processes to Performance Assessment (PA) for the unsaturated zone (UZ); (3) Provide a basis for development of an abstracted model for use in PA calculations.

  13. Structures and Stabilization Mechanisms in Chemically Stabilized Ceramics

    Science.gov (United States)

    Gai-Boyes, Pratibha L.; Saltzberg, Michael A.; Vega, Alexander

    1993-09-01

    Structural complexities and disorder in chemically stabilized cristobalites (CSC), which are room temperature silica-based ceramics, prepared by a wet chemical route, are described. CSC displays many of the structural characteristics of the high temperature cristobalite, elucidated by HREM and X-ray diffraction. In-situ electron diffraction and NMR results suggest that the disorder is structural and is static.

  14. Electrostatic Stabilized InP Colloidal Quantum Dots with High Photoluminescence Efficiency.

    Science.gov (United States)

    Mnoyan, Anush N; Kirakosyan, Artavazd Gh; Kim, Hyunki; Jang, Ho Seong; Jeon, Duk Young

    2015-06-30

    Electrostatically stabilized InP quantum dots (QDs) showing a high luminescence yield of 16% without any long alkyl chain coordinating ligands on their surface are demonstrated. This is achieved by UV-etching the QDs in the presence of fluoric and sulfuric acids. Fluoric acid plays a critical role in selectively etching nonradiative sites during the ligand-exchange process and in relieving the acidity of the solution to prevent destruction of the QDs. Given that the InP QDs show high luminescence without any electrical barriers, such as long alkyl ligands or inorganic shells, this method can be applied for QD treatment for application to highly efficient QD-based optoelectronic devices.

  15. Dendronization-induced phase-transfer, stabilization and self-assembly of large colloidal Au nanoparticles

    Science.gov (United States)

    Malassis, Ludivine; Jishkariani, Davit; Murray, Christopher B.; Donnio, Bertrand

    2016-07-01

    The phase-transfer of CTAB-coated aqueous, spherical gold nanoparticles, with metallic core diameters ranging from ca. 27 to 54 nm, into organic solvents by exchanging the primitive polar bilayer with lipophilic, disulfide dendritic ligands is reported. The presence of such a thick nonpolar organic shell around these large nanoparticles enhances their stabilization against aggregation, in addition to enabling their transfer into a variety of solvents such as chloroform, toluene or tetrahydrofuran. Upon the slow evaporation of a chloroform suspension deposited on a solid support, the dendronized hybrids were found to self-assemble into ring structures of various diameters. Moreover, their self-assembly at the liquid-air interface affords the formation of fairly long-range ordered monolayers, over large areas, that can then be entirely transferred onto solid substrates.The phase-transfer of CTAB-coated aqueous, spherical gold nanoparticles, with metallic core diameters ranging from ca. 27 to 54 nm, into organic solvents by exchanging the primitive polar bilayer with lipophilic, disulfide dendritic ligands is reported. The presence of such a thick nonpolar organic shell around these large nanoparticles enhances their stabilization against aggregation, in addition to enabling their transfer into a variety of solvents such as chloroform, toluene or tetrahydrofuran. Upon the slow evaporation of a chloroform suspension deposited on a solid support, the dendronized hybrids were found to self-assemble into ring structures of various diameters. Moreover, their self-assembly at the liquid-air interface affords the formation of fairly long-range ordered monolayers, over large areas, that can then be entirely transferred onto solid substrates. Electronic supplementary information (ESI) available: TEM microscope images. See DOI: 10.1039/c6nr03404g

  16. Adsorption of water-soluble polymers onto barium titanate and its effects on colloidal stability

    NARCIS (Netherlands)

    Laat, de A.W.M.

    1995-01-01

    Ceramic products are usually made from powders which are processed into a green body, with a shape dictated by the final product. Organic binders are used to give the green product sufficient mechanical strength. A sintering process at high temperature converts the green body into the final ceramic

  17. Adsorption of water-soluble polymers onto barium titanate and its effect on colloidal stability.

    NARCIS (Netherlands)

    Laat, de A.W.M.

    1995-01-01

    Ceramic products are usually made from powders which are processed into a green body, with a shape dictated by the final product. Organic binders are used to give the green product sufficient mechanical strength. A sintering process at high temperature converts the green body into the final ceramic

  18. High-Resolution Transmission Electron Microscopy Observation of Colloidal Nanocrystal Growth Mechanisms using Graphene Liquid Cells

    Energy Technology Data Exchange (ETDEWEB)

    Yuk, Jong Min; Park, Jungwon; Ercius, Peter; Kim, Kwanpyo; Hellebusch, Danny J.; Crommie, Michael F.; Lee, Jeong Yong; Zettl, A.; Alivisatos, A. Paul

    2011-12-12

    We introduce a new type of liquid cell for in-situ electron microscopy based upon entrapment of a liquid film between layers of graphene. We employ this cell to achieve high-resolution imaging of colloidal platinum nanocrystal growth. The ability to directly image and resolve critical steps at atomic resolution provides new insights into nanocrystal coalescence and reshaping during growth.

  19. Colloidal organization

    CERN Document Server

    Okubo, Tsuneo

    2015-01-01

    Colloidal Organization presents a chemical and physical study on colloidal organization phenomena including equilibrium systems such as colloidal crystallization, drying patterns as an example of a dissipative system and similar sized aggregation. This book outlines the fundamental science behind colloid and surface chemistry and the findings from the author's own laboratory. The text goes on to discuss in-depth colloidal crystallization, gel crystallization, drying dissipative structures of solutions, suspensions and gels, and similar-sized aggregates from nanosized particles. Special emphas

  20. Colloidal stability of carbonate-coated silver nanoparticles in synthetic and natural freshwater.

    Science.gov (United States)

    Piccapietra, Flavio; Sigg, Laura; Behra, Renata

    2012-01-17

    To gain important information on fate, mobility, and bioavailability of silver nanoparticles (AgNP) in aquatic systems, the influence of pH, ionic strength, and humic substances on the stability of carbonate-coated AgNP (average diameter 29 nm) was systematically investigated in 10 mM carbonate and 10 mM MOPS buffer, and in filtered natural freshwater. Changes in the physicochemical properties of AgNP were measured using nanoparticle tracking analysis, dynamic light scattering, and ultraviolet-visible spectroscopy. According to the pH-dependent carbonate speciation, below pH 4 the negatively charged surface of AgNP became positive and increased agglomeration was observed. Electrolyte concentrations above 2 mM Ca(2+) and 100 mM Na(+) enhanced AgNP agglomeration in the synthetic media. In the considered concentration range of humic substances, no relevant changes in the AgNP agglomeration state were measured. Agglomeration of AgNP exposed in filtered natural freshwater was observed to be primarily controlled by the electrolyte type and concentration. Moreover, agglomerated AgNP were still detected after 7 days of exposure. Consequently, slow sedimentation and high mobility of agglomerated AgNP could be expected under the considered natural conditions. A critical evaluation of the different methods used is presented as well.

  1. Crosslinking to enhance colloidal stability and redispersity of layered double hydroxide nanoparticles.

    Science.gov (United States)

    Zuo, Huali; Gu, Zi; Cooper, Helen; Xu, Zhi Ping

    2015-12-01

    This article introduces a strategy for stabilizing and redispersing layered double hydroxide (LDH) nanoparticles by crosslinking bovine serum albumin (BSA) coated onto the surface. The strategy involves optimization of the amount of the crosslinking agent glutaraldehyde (GTA) to achieve minimal aggregation and ready redispersion. LDH nanoparticles were prepared by co-precipitation and hydrothermal treatment, with subsequent BSA coating at the BSA/LDH mass ratio of 5:2. BSA coated onto LDH nanoparticles was crosslinked with different amounts of GTA. Aggregation studies using dilution assays, dynamic light scattering, and zeta potential analysis indicated that severe aggregation at lower LDH nanoparticle concentrations can be prevented by proper crosslinking of BSA with GTA. The GTA-crosslinked BSA-coated nanoparticles showed excellent redispersity compared to the non-crosslinked nanoparticles. In vitro cytotoxicity and cell uptake were found to be minimally affected by GTA-crosslinking. The new strategy therefore provides a much more effective method for the prevention of LDH nanoparticle aggregation and improved LDH nanoparticle redispersion for use in a wide variety of bio-applications in vitro and in vivo.

  2. Biocompatible gold nanorods: one-step surface functionalization, highly colloidal stability, and low cytotoxicity.

    Science.gov (United States)

    Liu, Kang; Zheng, Yuanhui; Lu, Xun; Thai, Thibaut; Lee, Nanju Alice; Bach, Udo; Gooding, J Justin

    2015-05-05

    The conjugation of gold nanorods (AuNRs) with polyethylene glycol (PEG) is one of the most effective ways to reduce their cytotoxicity arising from the cetyltrimethylammonium bromide (CTAB) and silver ions used in their synthesis. However, typical PEGylation occurs only at the tips of the AuNRs, producing partially modified AuNRs. To address this issue, we have developed a novel, facile, one-step surface functionalization method that involves the use of Tween 20 to stabilize AuNRs, bis(p-sulfonatophenyl)phenylphosphine (BSPP) to activate the AuNR surface for the subsequent PEGylation, and NaCl to etch silver from the AuNRs. This method allows for the complete removal of the surface-bound CTAB and the most active surface silver from the AuNRs. The produced AuNRs showed far lower toxicity than other methods to PEGylate AuNRs, with no apparent toxicity when their concentration is lower than 5 μg/mL. Even at a high concentration of 80 μg/mL, their cell viability is still four times higher than that of the tip-modified AuNRs.

  3. Charge-Controlled Colloids on Liquid-Liquid Interfaces

    Science.gov (United States)

    Kunz, Daniel A.; Reck, Bernd; Manoharan, Vinothan N.

    2014-03-01

    The tendency of colloidal particles to stabilize interfaces has been exploited for many years to generate Pickering emulsions with a variety of industrial applications. However, the exact stabilization mechanism and its dependence on the surface properties of the colloidal particles are not yet fully understood. We provide new interfacial studies on the nonequilibrium dynamics of a colloidal system with tunable surface charge density. We push individual sub-micron colloidal particles towards an oil-water interface and track their motion in three-dimensions using holographic microscopy to examine the influence of zeta potential on the dynamics of the system. This project was funded by the BASF Advanced Research Initiative, BASF SE, Germany.

  4. The Mechanics of Gross Moist Stability

    Directory of Open Access Journals (Sweden)

    Zeljka Fuchs

    2009-08-01

    Full Text Available The gross moist stability relates the net lateral outflow of moist entropy or moist static energy from an atmospheric convective region to some measure of the strength of the convection in that region. If the gross moist stability can be predicted as a function of the local environmental conditions, then it becomes the key element in understanding how convection is controlled by the large-scale flow. This paper provides a guide to the various ways in which the gross moist stability is defined and the subtleties of its calculation from observations and models. Various theories for the determination of the gross moist stability are presented and its roles in current conceptual models for the tropical atmospheric circulation are analyzed. The possible effect of negative gross moist stability on the development and dynamics of tropical disturbances is currently of great interest.

  5. Mechanisms of meat batter stabilization: a review.

    Science.gov (United States)

    Gordon, A; Barbut, S

    1992-01-01

    Comminuted meat products are a complex mixture of muscle tissue, solubilized proteins, fat, salt, and water. The two theories that have been presented to explain meat batters stabilization are reviewed. The emulsion theory explains stabilization by the formation of a protein film around fat globules, whereas the physical entrapment theory emphasizes the role of the protein matrix in holding the fat in place during chopping and subsequent heating. However, some aspects of stabilization cannot be explained adequately by either one of these theories. In this article the role of meat proteins, aqueous phase, and lipid phase are examined in light of past and recent research findings.

  6. Study on Mechanism of Rare Earth PVC Stabilizer

    Institute of Scientific and Technical Information of China (English)

    彭振博; 胡斌; 苏庆德; 曲锦忠

    2003-01-01

    Rare earth compounds can be used as PVC thermal stabilizers. According to the infrared spectra of the mixture of PVC and some stearates, the mechanism of stabilization of different stearates was studied. The specialty of rare earth stabilizers was found. They can change the conformation of PVC and restrain the elimination of HCl. From this aspect, the unique synergetic effect with other stabilizers of rare earth compounds can be explained.

  7. Formation of aquatic Th(IV) colloids and stabilization by interaction with Cm(III)/Eu(III).

    Science.gov (United States)

    Yun, Jong-Il; Kim, Maria-Anna; Panak, Petra J; Kim, Jae-Il; Fanghänel, Thomas

    2006-03-23

    The present investigation is to ascertain under what conditions actinide ions undergo aggregation via oxo-bridging to form stable colloidal species. Eu and Th are taken for this purpose as trivalent and tetravalent actinide homologue ions, respectively. For verification of the effects of impurities in chemicals on the actinide colloid generation, pH is adjusted either by a conventional acid-base titration or by coulometry without addition of NaOH. The colloid generation is monitored by highly sensitive laser-induced breakdown detection in varying pH from 3 to 7, first in dilute Eu and Th solutions separately and then in a mixture of both, all in 0.5 M HCl/NaCl. The formation of stable colloids is observed particularly in a mixed solution of Eu and Th, suggesting that aggregation via mutual oxo-bridging of trivalent and tetravalent metal ions results in surface polarization, leading to stable hydrophilic particles of 20-30 nm in diameter. When Eu is replaced by Cm in the mixed solution in favor of the high fluorescence intensity of the latter, the chemical speciation is determined on colloid-borne Cm by time-resolved laser fluorescence spectroscopy. Two different colloid-borne Cm species, oxo-bridged with Th, are identified: a minor amount at 598.0 nm (denoted as Cm-Th(1)) and a major amount at 604.8 nm (Cm-Th(2)). The former is found as a transitional state, which converts to the latter with increasing pH and prevails at pH > 5.5. Both colloid-borne species (Cm-Th) are distinctively different from hydrolyzed Cm or its carbonate complexes with respect to their fluorescence peak positions and lifetimes. In conclusion, a mixed oxo-bridging of trivalent and tetravalent actinides elicits the generation of stable colloids, whereas individual ions in their pure state form colloids under oversaturation at near neutral pH only as a transitional state for precipitation.

  8. [Toxicological evaluation of nanosized colloidal silver, stabilized with polyvinylpyrrolidone, in 92-day experiment on rats. II. Internal organs morphology].

    Science.gov (United States)

    Zaytseva, N V; Zemlyanova, M A; Zvezdin, V N; Dovbysh, A A; Gmoshinsky, I V; Khotimchenko, S A; Akafieva, T I

    2016-01-01

    The aim of the study was to evaluate the safe doses of commercially available nanosized colloidal silver (NCS), stabilized with polyvinilpirrolidone (PVP, food additive E1201) when administered in gastrointestinal tract of rats in the 92-day experiment in terms of the morphological changes in the internals of animals. The sample studied contained non-aggregated nanoparticles (NPs) of silver belonging to size fractions with a diameter of less than 5 nm, 10-20 nm or 50-80 nm. 80% of NPs were inside the range of hydrodynamic diameters 10.6-61.8 nm. The preparation of NCS was administered to growing male Wistar rats. (initial body weight 80 ± 10 g) for 1 month by intragastric gavage and then consumed with food at doses of 0.1, 1.0 and 10 mg/kg of body weight based on silver. The control animals received water or vehicle of nanomaterial--water solution of PVP. After withdrawal of animals from the experiment by exsanguination under ether anesthesia organs (liver, spleen, kidney, ileum) were isolated and their slides were prepared by standard methods following 'by staining with hematoxylin-eosin. Analysis was performed in light optical microscope equipped with a digital camera at a magnification from 1 x 100 to 1 x 1000. It was shown that the experimental animals treated with the NCS developed series of morphological changes in the tissues of the internal organs (liver, spleen and kidney) with the elevation of the range and severity of structural changes with increasing doses of silver. The most sensitive target of NCS action was apparently liver, which has already shown at a dose of 0.1 mg of silver NP/kg of body weight marked eosinophilic infiltration of portal tracts, which was accompanied at doses of 1.0 and 10.0 mg/kg by the emergence of medium and large-drop fat vacuoles in the cytoplasm of hepatocytes, swelling and lympho-macrophage. infiltration of the portal tracts. Detectable changes can be regarded as symptoms of inflammation of hepatocytes, at least, at a

  9. Thermodynamic stabilization of colloids

    NARCIS (Netherlands)

    Stol, R.J.; Bruyn, P.L. de

    1980-01-01

    An analysis is given of the conditions necessary for obtaining a thermodynamically stable dispersion (TSD) of solid particles in a continuous aqueous solution phase. The role of the adsorption of potential-determining ions at the planar interface in lowering the interfacial free energy (γ) to promot

  10. Formation of colloidal silver nanoparticles stabilized by Na+-poly(gamma-glutamic acid)-silver nitrate complex via chemical reduction process.

    Science.gov (United States)

    Yu, Da-Guang

    2007-10-01

    Macromolecular and polyanionic Na(+)-poly(gamma-glutamic acid) (PGA) silver nitrate complex acted as both a metal ion provider and a particle protector to fabricate nanosized silver colloids under chemical reduction by dextrose. The formation and size of particles have been characterized from transmission electron microscopy (TEM), dynamic light scattering analysis and UV-vis spectrophotometer. The results showed that the average particle size was 17.2+/-3.4 to 37.3+/-5.5 nm, apparently depending on the complex concentration. It was found that the rate constant and conversion of silver nanoparticles were proportional to the concentration of PGA. The growth mechanism of nanosized silver colloid was fully discussed. In addition, the in vitro cytotoxicity evaluated by L929 fibroblasts proliferation and antibacterial activity against Gram-positive strain (methicillin-resistant S. aureus (MRSA)) and Gram-negative strain (P. aeruginosa) bacteria have been assessed.

  11. Protocol optimization for the mild detemplation of mesoporous silica nanoparticles resulting in enhanced texture and colloidal stability

    NARCIS (Netherlands)

    Zhang, Zheng; Mayoral, Alvaro; Melian-Cabrera, Ignacio

    2016-01-01

    Porosity development of mesostructured colloidal silica nanoparticles is related to the removal of the organic templates and co-templates which is often carried out by calcination at high temperatures, 500 -600 degrees C. In this study a mild detemplation method based on the oxidative Fenton chemist

  12. A Review on Nanofluids: Preparation, Stability Mechanisms, and Applications

    OpenAIRE

    Wei Yu; Huaqing Xie

    2012-01-01

    Nanofluids, the fluid suspensions of nanomaterials, have shown many interesting properties, and the distinctive features offer unprecedented potential for many applications. This paper summarizes the recent progress on the study of nanofluids, such as the preparation methods, the evaluation methods for the stability of nanofluids, and the ways to enhance the stability for nanofluids, the stability mechanisms of nanofluids, and presents the broad range of current and future applications in var...

  13. Force spectroscopy predicts thermal stability of immobilized proteins by measuring microbead mechanics.

    Science.gov (United States)

    Gregurec, Danijela; Velasco-Lozano, Susana; Moya, Sergio E; Vázquez, Luis; López-Gallego, Fernando

    2016-10-26

    Optimal immobilization of enzymes on porous microbeads enables the fabrication of highly active and stable heterogeneous biocatalysts to implement biocatalysis in synthetic and analytical chemistry. However, empirical procedures for enzyme immobilization still prevail over rational ones because there is an unmet need for more comprehensive characterization techniques that aid to understand and trace the immobilization process. Here, we present the use of atomic force spectroscopy (AFS) as an innovative solution to indirectly characterize immobilized proteins on porous materials and monitor the immobilization process in real time. We investigate the mechanical properties of porous agarose microbeads immobilizing proteins by indenting a colloidal probe (silica microparticle) into a single bead. AFS demonstrates that the binding of proteins to the solid matrix of an agarose microbead alters its stiffness. Interestingly, we discovered that irreversible and multivalent immobilizations that make microbeads stiffer also stabilize the immobilized proteins against the temperature. Hence, we propose atomic force spectroscopy as a useful technique to indirectly unravel the stability of the immobilized enzymes investigating the mechanics of the heterogenous biocatalysts as a solid biomaterial beyond the intrinsic mechanics of the proteins.

  14. Colloids with continuously tunable surface charge.

    Science.gov (United States)

    van Ravensteijn, Bas G P; Kegel, Willem K

    2014-09-09

    In this paper, we present a robust way to tune the surface potential of polystyrene colloids without changing the pH, ionic strength, etc. The colloids are composed of a cross-linked polystyrene core and a cross-linked vinylbenzyl chloride layer. Besides the chlorine groups, the particle surface contains sulfate/sulfonate groups (arising from the polymerization initiators) that provide a negative surface potential. Performing a Menschutkin reaction on the surface chlorine groups with tertiary amines allows us to introduce quaternary, positively charged amines. The overall charge on the particles is then determined by the ratio between the sulfate/sulfonate moieties and the quaternary amines. Using this process, we were able to invert the charge in a continuous manner without losing colloidal stability upon passing the isoelectric point. The straightforward reaction mechanism together with the fact that the reaction could be quenched rapidly resulted in a colloidal system in which the ζ potential can be tuned between -80 and 45 mV. As proof of principle, the positively charged particles were used in heterocoagulation experiments with nanometer- and micrometer-sized negatively charged silica particles to create geometrically well-defined colloidal (nano) clusters.

  15. Gold nanostar-polymer hybrids for siRNA delivery: Polymer design towards colloidal stability and in vitro studies on breast cancer cells.

    Science.gov (United States)

    Sardo, Carla; Bassi, Barbara; Craparo, Emanuela F; Scialabba, Cinzia; Cabrini, Elisa; Dacarro, Giacomo; D'Agostino, Agnese; Taglietti, Angelo; Giammona, Gaetano; Pallavicini, Piersandro; Cavallaro, Gennara

    2017-03-15

    To overcome the low bioavailability of siRNA (small interfering RNA) and to improve their transfection efficiency, the use of non-viral delivery carriers is today a feasible approach to transform the discovery of these incredibly potent and versatile drugs into clinical practice. Polymer-modified gold nanoconstructs (AuNCs) are currently viewed as efficient and safe intracellular delivery carriers for siRNA, as they have the possibility to conjugate the ability to stably entrap and deliver siRNAs inside cells with the advantages of gold nanoparticles, which can act as theranostic agents and radiotherapy enhancers through laser-induced hyperthermia. In this study, AuNCs were prepared by coating Gold Nano Stars (GNS) with suitable functionalised polymers, to give new insight on the choice of the coating in order to obtain colloidal stability, satisfying in vitro transfection behaviour and reliability in terms of homogeneous results upon GNS type changing. For this goal, GNS synthesized with three different sizes and shapes were coated with two different polymers: i) α-mercapto-ω-amino polyethylene glycol 3000Da (SH-PEG3000-NH2), a hydrophilic linear polymer; ii) PHEA-PEG2000-EDA-LA (PPE-LA), an amphiphilic hydroxyethylaspartamide copolymer containing a PEG moiety. Both polymers contain SH or SS groups for anchoring on gold surface and NH2 groups, which can be protonated in order to obtain a positive surface for successive siRNA layering. The effect of the features of the coating polymers on siRNA layering, and the extent of intracellular uptake and luciferase gene silencing effect were evaluated for each of the obtained coated GNS. The results highlight that amphiphilic biocompatible polymers with multi-grafting function are more suitable for ensuring the colloidal stability and the effectiveness of these colloidal systems, compared to the coating with linear PEG. Copyright © 2017 Elsevier B.V. All rights reserved.

  16. Photo-stability and time-resolved photoluminescence study of colloidal CdSe/ZnS quantum dots passivated in Al2O3 using atomic layer deposition

    Science.gov (United States)

    Cheng, Chih-Yi; Mao, Ming-Hua

    2016-08-01

    We report photo-stability enhancement of colloidal CdSe/ZnS quantum dots (QDs) passivated in Al2O3 thin film using the atomic layer deposition (ALD) technique. 62% of the original peak photoluminescence (PL) intensity remained after ALD. The photo-oxidation and photo-induced fluorescence enhancement effects of both the unpassivated and passivated QDs were studied under various conditions, including different excitation sources, power densities, and environment. The unpassivated QDs showed rapid PL degradation under high excitation due to strong photo-oxidation in air while the PL intensity of Al2O3 passivated QDs was found to remain stable. Furthermore, recombination dynamics of the unpassivated and passivated QDs were investigated by time-resolved measurements. The average lifetime of the unpassivated QDs decreases with laser irradiation time due to photo-oxidation. Photo-oxidation creates surface defects which reduces the QD emission intensity and enhances the non-radiative recombination rate. From the comparison of PL decay profiles of the unpassivated and passivated QDs, photo-oxidation-induced surface defects unexpectedly also reduce the radiative recombination rate. The ALD passivation of Al2O3 protects QDs from photo-oxidation and therefore avoids the reduction of radiative recombination rate. Our experimental results demonstrated that passivation of colloidal QDs by ALD is a promising method to well encapsulate QDs to prevent gas permeation and to enhance photo-stability, including the PL intensity and carrier lifetime in air. This is essential for the applications of colloidal QDs in light-emitting devices.

  17. Band-gap engineering by molecular mechanical strain-induced giant tuning of the luminescence in colloidal amorphous porous silicon nanostructures

    KAUST Repository

    Mughal, Asad Jahangir

    2014-01-01

    Nano-silicon is a nanostructured material in which quantum or spatial confinement is the origin of the material\\'s luminescence. When nano-silicon is broken into colloidal crystalline nanoparticles, its luminescence can be tuned across the visible spectrum only when the sizes of the nanoparticles, which are obtained via painstaking filtration methods that are difficult to scale up because of low yield, vary. Bright and tunable colloidal amorphous porous silicon nanostructures have not yet been reported. In this letter, we report on a 100 nm modulation in the emission of freestanding colloidal amorphous porous silicon nanostructures via band-gap engineering. The mechanism responsible for this tunable modulation, which is independent of the size of the individual particles and their distribution, is the distortion of the molecular orbitals by a strained silicon-silicon bond angle. This mechanism is also responsible for the amorphous-to-crystalline transformation of silicon. This journal is

  18. Band-gap engineering by molecular mechanical strain-induced giant tuning of the luminescence in colloidal amorphous porous silicon nanostructures.

    Science.gov (United States)

    Mughal, A; El Demellawi, J K; Chaieb, Sahraoui

    2014-12-14

    Nano-silicon is a nanostructured material in which quantum or spatial confinement is the origin of the material's luminescence. When nano-silicon is broken into colloidal crystalline nanoparticles, its luminescence can be tuned across the visible spectrum only when the sizes of the nanoparticles, which are obtained via painstaking filtration methods that are difficult to scale up because of low yield, vary. Bright and tunable colloidal amorphous porous silicon nanostructures have not yet been reported. In this letter, we report on a 100 nm modulation in the emission of freestanding colloidal amorphous porous silicon nanostructures via band-gap engineering. The mechanism responsible for this tunable modulation, which is independent of the size of the individual particles and their distribution, is the distortion of the molecular orbitals by a strained silicon-silicon bond angle. This mechanism is also responsible for the amorphous-to-crystalline transformation of silicon.

  19. Microcapsule mechanics: from stability to function.

    Science.gov (United States)

    Neubauer, Martin P; Poehlmann, Melanie; Fery, Andreas

    2014-05-01

    Microcapsules are reviewed with special emphasis on the relevance of controlled mechanical properties for functional aspects. At first, assembly strategies are presented that allow control over the decisive geometrical parameters, diameter and wall thickness, which both influence the capsule's mechanical performance. As one of the most powerful approaches the layer-by-layer technique is identified. Subsequently, ensemble and, in particular, single-capsule deformation techniques are discussed. The latter generally provide more in-depth information and cover the complete range of applicable forces from smaller than pN to N. In a theory chapter, we illustrate the physics of capsule deformation. The main focus is on thin shell theory, which provides a useful approximation for many deformation scenarios. Finally, we give an overview of applications and future perspectives where the specific design of mechanical properties turns microcapsules into (multi-)functional devices, enriching especially life sciences and material sciences.

  20. On a stabilization mechanism for low-velocity detonations

    KAUST Repository

    Sow, Aliou

    2017-03-08

    We use numerical simulations of the reactive Lula equations to analyse the nonlinear stability of steady-state one-dimensional solutions for gaseous detonations in the presence of both momentum and heat losses. Our results point to a possible stabilization mechanism for the low-velocity detonations in such systems. The mechanism stems from the existence of a one-parameter family of solutions found in Semenko el al.

  1. 纳米片状ZnO的室温制备及其胶状前体的稳定性分析%Synthesis of ZnO Nano Flake at Room Temperature and the Stability of Colloidal Precursors

    Institute of Scientific and Technical Information of China (English)

    许泳吉; 张利; 赵雪萍

    2012-01-01

    Colloidal precursors were synthesized by precipitation method using zinc acetate ( ZnAc2 ) and sodium hydroxide(NaOH) aqueous solution at room temperature. The products of Zns (OH)8 ( Ac)2 ·2H2O and ZnO were prepared by controlling the pH values of the reaction system. The composition, structure, and morphology of the resultant soild were characterized by using X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer. We found that when the pH value of the precursor solution was 7, a steady colloid could be synthesized by the precipitation method, and the composition of the product was Zn5 ( OH)8 ( Ac ) 2 · 2 H2 O after dried at room temperature. If the pH value was 14, the coagulation phenomenon occurred with the ageing of colloidal precursor, and the coagulation product was hexagonal flake ZnO. In addition, the growth mechanism of ZnO nanomaterials was discussed, and it was also considered from the effects of pH value on the stability of colloidal precursor.%以醋酸锌和氢氧化钠为原料,采用室温直接沉淀法得到了ZnO的前体胶状醋酸锌碱式盐,通过控制pH值,在室温下分别制备了碱式盐Zn5(OH)8(Ac)2·2H2O和六方晶系纤锌矿ZnO,并利用X射线衍射、扫描电子显微镜和能谱(EDS)等测试技术对产物进行表征.结果表明,采用直接沉淀法在pH值为7的环境下得到了具有{n{[Zn5(OH)8(H2O)2]2+}·(2n-x)Ac-}x+·xAc-胶团结构的稳定胶体体系,室温下干燥后的产物的成分为碱式盐Zn5(OH)8(Ac)2 ·2H2O;而在pH值为14时,胶状前体发生聚沉生成白色沉淀,室温干燥后得到纳米片状ZnO.还考察了pH值对胶状前体稳定性的影响,并探讨了ZnO的生成机理.

  2. FINANCIAL MECHANISM OF SMALL ENTERPRISES STABILITY

    Directory of Open Access Journals (Sweden)

    G.M. Zaloznaya

    2007-03-01

    Full Text Available Rates of growth of parameters of development and role of small enterprises in economy of Russia and its regions today it is much less, than in the developed countries of the world. The significant role in the decision of this problem belongs to the financial mechanism. The complex changes of financial attitudes directed on increase of efficiency of functioning of the enterprises of small business are necessary. In this connection experience of the Orenburg area on formation of system of support of small business is reasonably interesting, and also its involving in development of real sector of economy and the decision of social questions of region.

  3. EDITORIAL: Colloidal suspensions Colloidal suspensions

    Science.gov (United States)

    Petukhov, Andrei; Kegel, Willem; van Duijneveldt, Jeroen

    2011-05-01

    N W 2002 Nature 416 811 [9] Borsboom M et al 1998 J. Synchrotron Radiat. 5 518 [10] Zernike F and Prins J A 1927 Z. Phys. 41 184 Colloidal suspensions contents How much does the core structure of a three-phase contact line contribute to the line tension near a wetting transition? J O Indekeu, K Koga and B Widom A systematic coarse-graining strategy for semi-dilute copolymer solutions: from monomers to micelles Barbara Capone, Ivan Coluzza and Jean-Pierre Hansen Structural searches using isopointal sets as generators: densest packings for binary hard sphere mixtures Toby S Hudson and Peter Harrowell The theory of delamination during drying of confined colloidal suspensions K J Wallenstein and W B Russel Electrostatics Modeling of equilibrium hollow objects stabilized by electrostatics Ethayaraja Mani, Jan Groenewold and Willem K Kegel The Donnan equilibrium: I. On the thermodynamic foundation of the Donnan equation of state A Philipse and A Vrij Colloidal rods and platelets Cholesteric order in systems of helical Yukawa rods H H Wensink and G Jackson Magnetic-field-induced nematic-nematic phase separation and droplet formation in colloidal goethite E van den Pol, A A Verhoeff, A Lupascu, M A Diaconeasa, P Davidson, I Dozov, B W M Kuipers, D M E Thies-Weesie and G J Vroege Structure of colloidal sphere-plate mixtures N Doshi, G Cinacchi, J S van Duijneveldt, T Cosgrove, S W Prescott, I Grillo, J Phipps and D I Gittins 3D structure of nematic and columnar phases of hard colloidal platelets A B G M Leferink op Reinink, J M Meijer, D Kleshchanok, D V Byelov, G J Vroege, A V Petukhov and H N W Lekkerkerker Phase behaviour of binary mixtures of diamagnetic colloidal platelets in an external magnetic field Jonathan Phillips and Matthias Schmidt Rheo-SAXS investigation of shear-thinning behaviour of very anisometric repulsive disc-like clay suspensions A M Philippe, C Baravian, M Imperor-Clerc, J De Silva, E Paineau, I Bihannic, P Davidson, F Meneau, P Levitz and L J Michot

  4. A Long-term Mechanism Needed to Safeguard Financial Stability

    Institute of Scientific and Technical Information of China (English)

    何德旭

    2007-01-01

    In the post-WTO era, China has encountered new difficulties in maintaining financial stability. Quick fix and emergency measures can no longer be relied on in the long run, and therefore, a long-term mechanism of financial stability must be put in place. This article recommends that China should focus on furthering financial reform, accelerating financial innovation and improving the legal system to promote a strong and competitive finance industry that is less vulnerable to financial hazards.

  5. Metelitsyn's inequality and stability criteria for mechanical systems

    DEFF Research Database (Denmark)

    Kliem, Wolfhard; Seyranian, A. P.

    2004-01-01

    Criteria of asymptotic stability for general linear mechanical systems are investigated. It is shown that the inequality first derived by Metelitsyn (1952) is a sufficient but not necessary condition for asymptotic stability. We argue that this inequality is of little use in applications....... Metelitsyn's theorems based on his inequality as well as critical comments in the literature on these theorems are analysed. Practical sufficient stability criteria are obtained in terms of extreme eigenvalues of the system matrices. This analysis is of special value for rotor systems in a complex setting...

  6. Mechanical stability of ordered droplet packings in microfluidic channels

    Science.gov (United States)

    Fleury, Jean-Baptiste; Claussen, Ohle; Herminghaus, Stephan; Brinkmann, Martin; Seemann, Ralf

    2011-12-01

    The mechanical response and stability of one and two-row packing of monodisperse emulsion droplets are studied in quasi 2d microchannels under longitudinal compression. Depending on the choice of parameter, a considered droplet arrangement is either transformed continuously into another packing under longitudinal compression or becomes mechanically unstable and segregates into domains of higher and lower packing fraction. Our experimental results are compared to analytical calculations for 2d-droplet arrangements with good quantitative agreement. This study also predicts important consequences for the stability of droplet arrangements in flowing systems.

  7. The influence of ionic strength and mixing ratio on the colloidal stability of PDAC/PSS polyelectrolyte complexes.

    Science.gov (United States)

    Zhang, Yanpu; Yildirim, Erol; Antila, Hanne S; Valenzuela, Luis D; Sammalkorpi, Maria; Lutkenhaus, Jodie L

    2015-10-01

    Polyelectrolyte complexes (PECs) form by mixing polycation and polyanion solutions together, and have been explored for a variety of applications. One challenge for PEC processing and application is that under certain conditions the as-formed PECs aggregate and precipitate out of suspension over the course of minutes to days. This aggregation is governed by several factors such as electrostatic repulsion, van der Waals attractions, and hydrophobic interactions. In this work, we explore the boundary between colloidally stable and unstable complexes as it is influenced by polycation/polyanion mixing ratio and ionic strength. The polymers examined are poly(diallyldimethylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate) (PSS). Physical properties such as turbidity, hydrodynamic size, and zeta potential are investigated upon complex formation. We also perform detailed molecular dynamics simulations to examine the structure and effective charge distribution of the PECs at varying mixing ratios and salt concentrations to support the experimental findings. The results suggest that the colloidally stable/unstable boundary possibly marks the screening effects from added salt, resulting in weakly charged complexes that aggregate. At higher salt concentrations, the complexes initially form and then gradually dissolve into solution.

  8. Stability Analysis for Compliant Constant-Force Compression Mechanisms

    Directory of Open Access Journals (Sweden)

    Ikechukwu Celestine UGWUOKE

    2009-12-01

    Full Text Available Stability analysis in compliant mechanism (CM design is of utmostimportance. From a practical point of view, a CM that is unstable is of nosignificance (has no practical value. Three useful plots were considered in theevaluation of each of the dynamic models of nine configurations of compliantconstant-force compression mechanisms (CCFCMs for their stabilitycharacteristics, which includes the polar plot based on the Routh-Hurwitzstability criterion, the Bode plot, and the Nyquist diagram which considersstability in the real frequency domain. Frequency-domain stability criterion isvery useful for determining suitable approaches to adjusting the CCFCMparameters in order to increase its relative stability. The results obtained showthat the CCFCMs investigated do exhibit higher relative stability for highervalues of damping ratio, and for zero damping ratio, all the CCFCMsinvestigated were unstable. The result also show that for the CCFCMsinvestigated to be stable, damping ratio must be greater than 0.03 (ξ > 0.03and depending on what attributes are most desirable, the CCFCM parameterscan be optimized to achieve the desired results. Nyquist criterion provides uswith suitable information concerning the absolute stability and furthermore,can be utilized to define and ascertain the relative stability of a system.

  9. Stability and degradation mechanisms in organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ecker, Bernhard

    2012-04-26

    This thesis deals with stability improvements and the investigation of degradation mechanisms in organic solar cells. Organic solar cells have been in the focus of extensive academic research for over almost two decades and are currently entering the market in small scale applications. For successful large scale applications, next to the improvement of the power conversion efficiency, the stability of organic solar cells has to be increased. This thesis is dedicated to the investigation of novel materials and architectures to study stability-related issues and degradation mechanisms in order to contribute to the basic understanding of the working principles of organic solar cells. Here, impedance spectroscopy, a frequency domain technique, is used to gain information about stability and degradation mechanisms in organic solar cells. In combination with systematic variations in the preparation of solar cells, impedance spectroscopy gives the possibility to differentiate between interface and bulk dominated effects. Additionally, impedance spectroscopy gives access to the dielectric properties of the device, such as capacitance. This offers among other things the opportunity to probe the charge carrier concentration and the density of states. Another powerful way of evaluation is the combination of experimentally obtained impedance spectra with equivalent circuit modelling. The thesis presents results on novel materials and solar cell architectures for efficient hole and electron extraction. This indicates the importance of knowledge over interlayers and interfaces for improving both the efficiency and stability of organic solar cells.

  10. Links between the mechanics of ventilation and spine stability.

    Science.gov (United States)

    Wang, Simon; McGill, Stuart M

    2008-05-01

    Spine stability is ensured through isometric coactivation of the torso muscles; however, these same muscles are used cyclically to assist ventilation. Our objective was to investigate this apparent paradoxical role (isometric contraction for stability or rhythmic contraction for ventilation) of some selected torso muscles that are involved in both ventilation and support of the spine. Eight, asymptomatic, male subjects provided data on low back moments, motion, muscle activation, and hand force. These data were input to an anatomically detailed, biologically driven model from which spine load and a lumbar spine stability index was obtained. Results revealed that subjects entrained their torso stabilization muscles to breathe during demanding ventilation tasks. Increases in lung volume and back extensor muscle activation coincided with increases in spine stability, whereas declines in spine stability were observed during periods of low lung inflation volume and simultaneously low levels of torso muscle activation. As a case study, aberrant ventilation motor patterns (poor muscle entrainment), seen in one subject, compromised spine stability. Those interested in rehabilitation of patients with lung compromise and concomitant back troubles would be assisted with knowledge of the mechanical links between ventilation during tasks that impose spine loading.

  11. Control of the PEO chain conformation on nanoparticles by adsorption of PEO-block-poly(L-lysine) copolymers and its significance on colloidal stability and protein repellency.

    Science.gov (United States)

    Louguet, Stéphanie; Kumar, Anitha C; Guidolin, Nicolas; Sigaud, Gilles; Duguet, Etienne; Lecommandoux, Sébastien; Schatz, Christophe

    2011-11-01

    The physical adsorption of PEO(n)-b-PLL(m) copolymers onto silica nanoparticles and the related properties of poly(ethylene oxide) (PEO)-coated particles were studied as a function of the block copolymer composition. Copolymers adopt an anchor-buoy conformation at the particle surface owing to a preferential affinity of poly(L-lysine) (PLL) blocks with the silica surface over PEO blocks when a large excess of copolymer is used. The interdistance between PEO chains at particle surface is highly dependent on the size of PLL segments; a dense brush of PEO is obtained for short PLL blocks (DP = 10), whereas PEO chains adopt a so-called interacting "mushroom" conformation for large PLL blocks (DP = 270). The size of the PEO blocks does not really influence the copolymer surface density, but it has a strong effect on the PEO layer thickness as expected. Salt and protein stability studies led to similar conclusions about the effectiveness of a PEO layer with a dense brush conformation to prevent colloidal aggregation and protein adsorption. Besides, a minimal PEO length is required to get full stabilization properties; as a matter of fact, both PEO(45)-b-PLL(10) and PEO(113)-b-PLL(10) give rise to a PEO brush conformation but only the latter copolymer efficiently stabilizes the particles in the presence of salt or proteins.

  12. Chemical, thermal and mechanical stabilities of metal-organic frameworks

    Science.gov (United States)

    Howarth, Ashlee J.; Liu, Yangyang; Li, Peng; Li, Zhanyong; Wang, Timothy C.; Hupp, Joseph T.; Farha, Omar K.

    2016-03-01

    The construction of thousands of well-defined, porous, metal-organic framework (MOF) structures, spanning a broad range of topologies and an even broader range of pore sizes and chemical functionalities, has fuelled the exploration of many applications. Accompanying this applied focus has been a recognition of the need to engender MOFs with mechanical, thermal and/or chemical stability. Chemical stability in acidic, basic and neutral aqueous solutions is important. Advances over recent years have made it possible to design MOFs that possess different combinations of mechanical, thermal and chemical stability. Here, we review these advances and the associated design principles and synthesis strategies. We focus on how these advances may render MOFs effective as heterogeneous catalysts, both in chemically harsh condensed phases and in thermally challenging conditions relevant to gas-phase reactions. Finally, we briefly discuss future directions of study for the production of highly stable MOFs.

  13. Colloidal stability of CeO2 nanoparticles coated with either natural organic matter or organic polymers under various hydrochemical conditions

    Science.gov (United States)

    Dippon, Urs; Pabst, Silke; Klitzke, Sondra

    2016-04-01

    The worldwide marked for engineered nanoparticles (ENPs) is growing and concerns on the environmental fate- and toxicity of ENPs are rising. Understanding the transport of ENPs within and between environmental compartments such as surface water and groundwater is crucial for exposition modeling, risk assessment and ultimately the protection of drinking water resources. The transport of ENPs is strongly influenced by the surface properties and aggregation behavior of the particles, which is strongly controlled by synthetic and natural organic coatings. Both, surface properties and aggregation characteristics are also key properties for the industrial application of ENPs, which leads to the development and commercialization of an increasing number of surface-functionalized ENPs. These include metals and oxides such as Cerium dioxide (CeO2) with various organic coatings. Therefore, we investigate CeO2 ENPs with different surface coatings such as weakly anionic polyvinyl alcohol (PVA) or strongly anionic poly acrylic acid (PAA) with respect to their colloidal stability in aqueous matrix under various hydrochemical conditions (pH, ionic strength) and their transport behavior in sand filter columns. Furthermore, we investigate the interaction of naturally occurring organic matter (NOM) with CeO2 ENPs and its effect on surface charge (zeta potential), colloidal stability and transport. While uncoated CeO2 ENPs aggregate at pH > 4 in aqueous matrix, our results show that PAA and PVA surface coatings as well as NOM sorbed to CeO2-NP surfaces can stabilize CeO2 ENPs under neutral and alkaline pH conditions in 1 mM KCl solution. Under slightly acidic conditions, differences between the three particle types were observed. PVA can stabilize particle suspensions in presence of 1 mM KCl at pH > 4.3, PAA at pH >4.0 and NOM at >3.2. While the presence of KCl did not influence particle size of NOM-CeO2 ENPs, CaCl2 at >2 mM lead to aggregation. Further results on the influence of KCl

  14. Magnetic Assisted Colloidal Pattern Formation

    Science.gov (United States)

    Yang, Ye

    photoacids, which stabilized the structures after the external field was removed. This approach has potential applications in the fabrication of advanced materials. My thesis is arranged as follows. In Chapter 1, I present a brief background of general pattern formation and why I chose to investigate patterns formed in colloidal systems. I also provide a brief review of field-assisted manipulation techniques in order to motivate why I selected magnetic and acoustic field to study colloidal patterns. In chapter 2, I present the theoretical background of magnetic manipulation, which is the main technique used in my research. In this chapter, I will introduce the basic knowledge on magnetic materials and theories behind magnetic manipulation. The underlining thermodynamic mechanisms and theoretical/computational approaches in colloidal pattern formation are also briefly reviewed. In Chapter 3, I focus on using these concepts to study adhesion forces between particle and surfaces. In Chapter 4, I focus on exploring the ground states of colloidal patterns formed from the anti-ferromagnetic interactions of mixtures of particles, as a function of the particle volume fractions. In Chapter 5, I discuss my research on phase transformations of the well-ordered checkerboard phase formed from the equimolar mixture of magnetic and non-magnetic beads in ferrofluid, and I focus mainly on phase transformations in a slowly varying magnetic field. In Chapter 6, I discuss my work on the superimposed magnetic and acoustic field to study patterns formed from monocomponent colloidal suspensions under vertical confinement. Finally, I conclude my thesis in Chapter 7 and discuss future directions and open questions that can be explored in magnetic field directed self-organization in colloidal systems.

  15. THEORETICAL CONSIDERATIONS REGARDING THE AUTOMATIC FISCAL STABILIZERS OPERATING MECHANISM

    Directory of Open Access Journals (Sweden)

    Gondor Mihaela

    2012-07-01

    Full Text Available This paper examines the role of Automatic Fiscal Stabilizers (AFS for stabilizing the cyclical fluctuations of macroeconomic output as an alternative to discretionary fiscal policy, admitting its huge potential of being an anti crisis solution. The objectives of the study are the identification of the general features of the concept of automatic fiscal stabilizers and the logical assessment of them from economic perspectives. Based on the literature in the field, this paper points out the disadvantages of fiscal discretionary policy and argue the need of using Automatic Fiscal Stabilizers in order to provide a faster decision making process, shielded from political interference, and reduced uncertainty for households and business environment. The paper conclude about the need of using fiscal policy for smoothing the economic cycle, but in a way which includes among its features transparency, responsibility and clear operating mechanisms. Based on the research results the present paper assumes that pro-cyclicality reduces de effectiveness of the Automatic Fiscal Stabilizer and as a result concludes that it is very important to avoid the pro-cyclicality in fiscal rule design. Moreover, by committing in advance to specific fiscal policy action contingent on economic developments, uncertainty about the fiscal policy framework during a recession should be reduced. Being based on logical analysis and not focused on empirical, contextualized one, the paper presents some features of AFS operating mechanism and also identifies and systematizes the factors which provide its importance and national individuality. Reaching common understanding on the Automatic Fiscal Stabilizer concept as a institutional device for smoothing the gap of the economic cycles across different countries, particularly for the European Union Member States, will facilitate efforts to coordinate fiscal policy responses during a crisis, especially in the context of the fiscal

  16. Preparation, characterization and mechanical properties of microarc oxidation coating formed on titanium in Al(OH)3 colloidal solution

    Science.gov (United States)

    Li, Y.; Yao, B.; Long, B. Y.; Tian, H. W.; Wang, B.

    2012-04-01

    A ceramic coating with thickness of 20-70 μm was grown on titanium plate in Al(OH)3 colloidal solution by microarc oxidation (MAO) in constant current mode. It is found that the as-grown coating consists of rutile TiO2 phase together with a thin layer of Ai2TiO5 phase near the surface of the coating. After removing the Ai2TiO5 layer by polishing, a single phase of rutile TiO2 coating is achieved, which is different from results reported previously, where the coating is usually composed of two phases of rutile and anatase TiO2. It is suggested that the formation of the coating with single phase of rutile TiO2 is related to the existence of Al(OH)3 in the solution. The growth rate of the coating increases with increasing current density in the range of 17-23 A/dm2, but it increases little in the range of 23-30 A/dm2. The rutile TiO2 coating looks compactness and solidity in the coating grown in the density range of 17-23 A/dm2 but looseness and insubstantiality in the range of 23-30 A/dm2. The hardness and elastic modulus of the rutile TiO2 decreases with the density increasing. The mechanism of formation of the coating is discussed in the present work.

  17. Stability and structural dimension of access mechanized panel

    Institute of Scientific and Technical Information of China (English)

    LUO Yi-zhong; WU Ai-xiang; WANG Hong-jiang; LIU Xiang-ping

    2005-01-01

    To acquire a knowledge of the stress-strain state in the process of mining beforehand, a numerical method was used to simulate the stoping process of access mechanized panel mining in No. 3 ore-body of Tonglushan mine; and for the sake of obtaining better stability, the optimal panel dimension and access stoping sequence were researched. The results show that the integral stability of the mechanized panel of No. 3 ore-body is passable in the process of winning at full level height; the stability of panel tends to be worse gradually with continuous increasing of panel width; and the better width of access panel in No.3 ore-body is less than 52 m. It is indicated that 3D elasto-plastic finite element method can make a satisfactory study of numerical simulation on the panel stability and its structural dimension in the test for the upward access mechanized-panel mining. The results of the theoretical calculation and analysis accord with the actual situation from the field ground pressure monitoring.

  18. Synthesis and characterization of silver colloidal nanoparticles with different coatings for SERS application

    Energy Technology Data Exchange (ETDEWEB)

    Mikac, L.; Ivanda, M., E-mail: ivanda@irb.hr [Ruđer Bošković Institute, Laboratory for Molecular Physics (Croatia); Gotić, M. [Ruđer Bošković Institute, Laboratory for Synthesis of New Materials (Croatia); Mihelj, T. [Ruđer Bošković Institute, Laboratory for Synthesis and Processes of Self-assembling of Organic Molecules (Croatia); Horvat, L. [Ruđer Bošković Institute, Laboratory for Electron Microscopy (Croatia)

    2014-12-15

    Silver colloids were produced by chemical reduction of silver salt (silver nitrate, AgNO{sub 3}) solution. As reducing agents, trisodium citrate, sodium borohydride, ascorbic acid, polyvinylpyrrolidone, and glucose were used. The colloids were characterized by UV–Vis, DLS, zeta potential measurements, and SEM. The colloids were stabilized with negative groups or large molecules attached to their surface. The surface-enhanced Raman scattering (SERS) effect of stabilized nanoparticles was measured by using pyridine and rhodamine 6G molecules as analytes and NaNO{sub 3}, KCl, and KBr at different concentrations as aggregating agents. The best Raman signal enhancement was achieved using silver nanoparticles of 40 nm size reduced and stabilized with citrate. The SERS signal of analyte molecules was further enhanced with the addition of sodium borohydride as an alternative aggregating agent. The borohydride had the strongest impact on the SERS effect of the colloid consistent of large (0.5 µm) silver nanoparticles stabilized with aminodextran. The mixture colloid-borohydride-pyridine was stable for hours. The mechanism of borohydride in the colloids is discussed.

  19. On the conditional total stability of equilibrium for mechanical systems

    Directory of Open Access Journals (Sweden)

    L. Salvadori

    1991-05-01

    Full Text Available In connection with the problem of observability, properties of total stability restricted to classes of perturbations of the governing equations are discussed for the equilibrium of holonomic mechanical systems. These systems are subject to positional conservative and dissipative forces. The particular case of a null dissipation is included. The perturbations to which the total stability is restricted are those obtained by modifying the kinetic energy, the potential of the conservative force, and the dissipative terms, without altering the Lagrangian form of the equations of the motion.

  20. Preparation of colloidal graphene in quantity by electrochemical exfoliation.

    Science.gov (United States)

    Chen, Kunfeng; Xue, Dongfeng

    2014-12-15

    We reported the preparation of colloidal graphene in quantity via the anodic exfoliation of graphite in (NH4)2SO4 aqueous solution. In the currently designed electrochemical exfoliation route, mass high-quality graphene was produced within short reaction time, around 1h. The proposed electrochemical exfoliation mechanism showed that SO4(2-) and H2O can be intercalated into those graphite sheets, monolayer and few-layer graphene were obtained by the formation of gaseous SO2 and O2 within graphite sheets. Stability evaluation showed that our exfoliated colloidal graphene can be perfectly stabilized in DMF solvent more than 1 week. The colloidal graphene can be used to construct various simple and complex patterns by writing it on A4 paper, which can be applied to flexible printed electronic devices. Furthermore, colloidal graphene can show promising applications in the fabrication of binder- and additive-free electrodes for supercapacitors and lithium-ion batteries. Our present method shows huge potential for industrial-scale synthesis of high-quality graphene and further commercialization of graphene colloid for numerous advanced applications in flexible printed electronics and energy storage devices.

  1. Colloidal microcapsules: Surface engineering of nanoparticles for interfacial assembly

    Science.gov (United States)

    Patra, Debabrata

    2011-12-01

    Colloidal Microcapsules (MCs), i.e. capsules stabilized by nano-/microparticle shells are highly modular inherently multi-scale constructs with applications in many areas of material and biological sciences e.g. drug delivery, encapsulation and microreactors. These MCs are fabricated by stabilizing emulsions via self-assembly of colloidal micro/nanoparticles at liquid-liquid interface. In these systems, colloidal particles serve as modular building blocks, allowing incorporation of the particle properties into the functional capabilities of the MCs. As an example, nanoparticles (NPs) can serve as appropriate antennae to induce response by external triggers (e.g. magnetic fields or laser) for controlled release of encapsulated materials. Additionally, the dynamic nature of the colloidal assembly at liquid-liquid interfaces result defects free organized nanostructures with unique electronic, magnetic and optical properties which can be tuned by their dimension and cooperative interactions. The physical properties of colloidal microcapsules such as permeability, mechanical strength, and biocompatibility can be precisely controlled through the proper choice of colloids and preparation conditions for their. This thesis illustrates the fabrication of stable and robust MCs through via chemical crosslinking of the surface engineered NPs at oil-water interface. The chemical crosslinking assists NPs to form a stable 2-D network structure at the emulsion interface, imparting robustness to the emulsions. In brief, we developed the strategies for altering the nature of chemical interaction between NPs at the emulsion interface and investigated their role during the self-assembly process. Recently, we have fabricated stable colloidal microcapsule (MCs) using covalent, dative as well as non-covalent interactions and demonstrated their potential applications including encapsulation, size selective release, functional devices and biocatalysts.

  2. Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

    Energy Technology Data Exchange (ETDEWEB)

    Bouëssel du Bourg, Lila; Ortiz, Aurélie U.; Coudert, François-Xavier, E-mail: fx.coudert@chimie-paristech.fr [PSL Research University, Chimie ParisTech – CNRS, Institut de Recherche de Chimie Paris, 75005 Paris (France); Boutin, Anne [École Normale Supérieure, PSL Research University, Département de Chimie, Sorbonne Universités – UPMC Univ Paris 06, CNRS UMR 8640 PASTEUR, 24 rue Lhomond, 75005 Paris (France)

    2014-12-01

    Theoretical studies on the experimental feasibility of hypothetical Zeolitic Imidazolate Frameworks (ZIFs) have focused so far on relative energy of various polymorphs by energy minimization at the quantum chemical level. We present here a systematic study of stability of 18 ZIFs as a function of temperature and pressure by molecular dynamics simulations. This approach allows us to better understand the limited stability of some experimental structures upon solvent or guest removal. We also find that many of the hypothetical ZIFs proposed in the literature are not stable at room temperature. Mechanical and thermal stability criteria thus need to be considered for the prediction of new MOF structures. Finally, we predict a variety of thermal expansion behavior for ZIFs as a function of framework topology, with some materials showing large negative volume thermal expansion.

  3. Mechanical stability study of type IV cryomodule (ILC prototype)

    Energy Technology Data Exchange (ETDEWEB)

    McGee, M.W.; Doremus, R.; Wands, C.R.; /Fermilab

    2007-06-01

    An ANSYS modal and harmonic finite element analysis (FEA) was performed in order to investigate cryomodule design mechanical stability for the proposed International Linear Collider (ILC). The current cryomodule, designated Type IV or (T4CM), closely follows the Type III TESLA Test Facility (TTF) version used at DESY, with the exception of a proposed location of the superconducting (SC) quadrupole at the center. This analysis considered the stringent stability criteria established for the ILC, where vertical motion for the SC quadrupole is limited to the micron range at a few Hz. Model validation was achieved through Type III cryomodule vibration measurement studies performed at DESY. The effect of support location, support stiffness and other important parameters were considered in a parametric sensitivity study. FEA results, fast motion investigations and stabilization techniques are discussed.

  4. Mechanisms of stability of armored bubbles: FY 1995 progress report

    Energy Technology Data Exchange (ETDEWEB)

    Rossen, W.R.; Das, S.K.

    1996-04-01

    Experimental and theoretical studies of stabilization of liquid films between bubbles were undertaken as part of an effort to model gas release in waste tanks at the Hanford nuclear reservation. Synthetic Hanford waste created here showed solids accumulation at bubble surfaces and some stabilization of bubbles in a froth upon sparging with nitrogen. Dilational interfacial rheological measurements indicate increasing hydrophobicity with increasing EDTA concentration in the wastes. There is greater dilational elasticity of the interface with solid particles present on the interface. Theoretical modeling of a 2D liquid film between bubbles containing one row of solid particles suggests that in 3D such a film would be unstable unless the solids all touch. This hints at a possible mechanism for bubble stabilization, if it can be argued that slowly evolving interfaces, as bubbles grow toward each other in the sludge, have solids closely packed, but that rapid expansion of gas during a rollover event forces the films to expand without additional solids.

  5. Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

    Directory of Open Access Journals (Sweden)

    Lila Bouëssel du Bourg

    2014-12-01

    Full Text Available Theoretical studies on the experimental feasibility of hypothetical Zeolitic Imidazolate Frameworks (ZIFs have focused so far on relative energy of various polymorphs by energy minimization at the quantum chemical level. We present here a systematic study of stability of 18 ZIFs as a function of temperature and pressure by molecular dynamics simulations. This approach allows us to better understand the limited stability of some experimental structures upon solvent or guest removal. We also find that many of the hypothetical ZIFs proposed in the literature are not stable at room temperature. Mechanical and thermal stability criteria thus need to be considered for the prediction of new MOF structures. Finally, we predict a variety of thermal expansion behavior for ZIFs as a function of framework topology, with some materials showing large negative volume thermal expansion.

  6. Atomistic mechanisms governing structural stability change of zinc antimony thermoelectrics

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xiaolong [Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710054 (China); Lin, Jianping, E-mail: jaredlin@163.com [School of Materials Science and Engineering, Xiamen University of Technology, Xiamen 361024 (China); Qiao, Guanjun [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Wang, Zhao, E-mail: zwangzhao@gmail.com [Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710054 (China); State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)

    2015-01-05

    The structural stability of thermoelectric materials is a subject of growing importance for their energy harvesting applications. Here, we study the microscopic mechanisms governing the structural stability change of zinc antimony at its working temperature, using molecular dynamics combined with experimental measurements of the electrical and thermal conductivity. Our results show that the temperature-dependence of the thermal and electrical transport coefficients is strongly correlated with a structural transition. This is found to be associated with a relaxation process, in which a group of Zn atoms migrates between interstitial sites. This atom migration gradually leads to a stabilizing structural transition of the entire crystal framework, and then results in a more stable crystal structure of β–Zn{sub 4}Sb{sub 3} at high temperature.

  7. COLLOID RELEASE FROM DIFFERENT SOIL DEPTH

    Directory of Open Access Journals (Sweden)

    Gang Chen

    2013-01-01

    Full Text Available Naturally occurring clay colloidal particles are heavily involved in sediment processes in the subsurface soil. Due to the import ance of these processes in the subsurface environment, the transport of clay colloidal particles has been studied in several disciplines, including soil sciences, petr ology, hydrology, etc. Specifically, in environmental engineering, clay colloid re lease and transport in the sediments have been extensively investigated, which are motiv ated by environmental concerns such as colloid-facilitated contaminant transport in groundwater and the subsurface soil. Clay colloid release is resulted from physical alteration of subsurface sediments. Despite the potential importance of clay colloid activiti es, the detailed mechanisms of release and transport of clay colloidal particles with in natural sediments are poorly understood. Pore medium structure, properties and flow dynamics, etc. are factors that affect clay colloid generation, mobilization, and subse quent transport. Possible mechanisms of clay colloid generation in the sediments in clude precipitation, erosion and mobilization by changes in pore water chemistry and clay colloid release depends on a balance of applied hydrodynamic and resisting adhesive torques and forces. The coupled role of pore water chemistry and fluid hydrodynamics thus play key roles in controlling clay colloid release and transport in the sediment s. This paper investigated clay colloidal particle release and transport, especially th e colloidal particle release mechanisms as well as the process modeling in the sediments. In this research, colloidal particle release from intact sediment columns with variable length was examined and colloidal particle release curves were simulated using an im plicit, finite-difference scheme. Colloidal particle release rate coefficient was found to be an exponential function of the sediment depth. The simulated results demonstrated that transport parameters were

  8. Oil-in-water Pickering emulsions stabilized by colloidal particles from the water-insoluble protein zein

    OpenAIRE

    de Folter, J.W.J.; van Ruijven, M.W.M.; Velikov, K.

    2012-01-01

    Few fully natural and biocompatible materials are available for the effective particle-stabilization of emulsions since strict requirements, such as insolubility in both fluid phases and intermediate wettability, need to be met. In this paper, we demonstrate the first use of water-insoluble proteins, employing the corn protein zein as a representative of this family, as effective particle-stabilizers of oil-in-water emulsions of natural oils and water. For this purpose, we synthesized zein co...

  9. Clay Effect in the Electrochemical Stabilization of Colloidal CoO(OH Applied as a Modified Electrode

    Directory of Open Access Journals (Sweden)

    Lucéli Roloff

    2016-12-01

    Full Text Available In this work, a mixed material was prepared using a montmorillonite clay (denominated imported sodic, IS modified with colloidal cobalt (Co. The obtained mixed material (ISCo was characterized by X-ray diffractometry and simultaneous thermal analysis and used to modify the surface of a platinum electrode for electrochemical determination of oxalic acid. The electrochemical behavior of the ISCo material was evaluated by cyclic voltammetry and the performance as a sensor for oxalic acid was assessed by square wave voltammetry. The platinum electrode showed no response to peak current when the oxalic acid concentration was increased in the range of 4.99 x 10-4 to 4.95 x 10-3 mol L-1. On the other hand, the platinum electrode modified with the mixed material presented a linear response in the studied range with a detection limit of 2.55 × 10-4 mol L-1. DOI: http://dx.doi.org/10.17807/orbital.v0i0.876

  10. Impact of lysozyme on stability mechanism of nanozirconia aqueous suspension

    Energy Technology Data Exchange (ETDEWEB)

    Szewczuk-Karpisz, Katarzyna, E-mail: k.szewczuk-karpisz@wp.pl; Wiśniewska, Małgorzata

    2016-08-30

    Highlights: • Adsorption and stabilization-destabilization properties of lysozyme (LSZ) in the nanozirconia-biopolymer solution system were determined. • The stability measurements were performed using turbidimetric method. • Lysozyme macromolecules undergo adsorption on the ZrO{sub 2} surface under electrostatic adsorbent-adsorbate attraction, i.e. at pH 6 and 9. • The biopolymer adsorption impact on the zirconia stability varies at different pH values. - Abstract: The effect of lysozyme (LSZ) presence on the zirconium(IV) oxide (ZrO{sub 2}) aqueous suspension stability was examined. The applied zirconia contains mesopores (with a diameter about 30 nm) and its mean particle size is about 100 nm. To determine the stability mechanism of ZrO{sub 2} suspension in the biopolymer presence, the adsorption and electrokinetic (surface charge density and zeta potential) measurements were performed in the pH range 3–10. The lysozyme adsorption on the nanozirconia surface proceeds mainly through electrostatic forces. Under solid-polymer repulsion conditions, there is no adsorption of lysozyme (pH < 6, C{sub NaCl} 0.01 mol/dm{sup 3}). The increase of solution ionic strength to 0.2 mol/dm{sup 3} causes screening of unfavourable forces and biopolymer adsorption becomes possible. The LSZ addition to the ZrO{sub 2} suspension influences its stability. At pH 3, 4.6 and 7.6, slight improvement of the system stability was obtained. In turn, at pH 9 considerable destabilization of nanozirconia particles covered by polymeric layers occurs.

  11. Evolution of the Stability Work from Classic Retaining Walls to Mechanically Stabilized Earth Walls

    Directory of Open Access Journals (Sweden)

    Anghel Stanciu

    2008-01-01

    Full Text Available For the consolidation of soil mass and the construction of the stability works for roads infrastructure it was studied the evolution of these kinds of works from classical retaining walls - common concrete retaining walls, to the utilization in our days of the modern and competitive methods - mechanically stabilized earth walls. Like type of execution the variety of the reinforced soil is given by the utilization of different types of reinforcing inclusions (steel strips, geosynthetics, geogrids or facing (precast concrete panels, dry cast modular blocks, metal sheets and plates, gabions, and wrapped sheets of geosynthetics.

  12. Conformational mechanism for the stability of microtubule-kinetochore attachments

    CERN Document Server

    Bertalan, Zsolt; Maiato, Helder; Zapperi, Stefano

    2014-01-01

    Regulating the stability of microtubule(MT)-kinetochore attachments is fundamental to avoiding mitotic errors and ensure proper chromosome segregation during cell division. While biochemical factors involved in this process have been identified, its mechanics still needs to be better understood. Here we introduce and simulate a mechanical model of MT-kinetochore interactions in which the stability of the attachment is ruled by the geometrical conformations of curling MT-protofilaments entangled in kinetochore fibrils. The model allows us to reproduce with good accuracy in vitro experimental measurements of the detachment times of yeast kinetochores from MTs under external pulling forces. Numerical simulations suggest that geometrical features of MT-protofilaments may play an important role in the switch between stable and unstable attachments.

  13. Electroweak Vacuum Stability and the Seesaw Mechanism Revisited

    CERN Document Server

    Ng, John

    2015-01-01

    We study the electroweak vacuum stability in Type I seesaw models for 3 generations of neutrinos in scenarios where the right-handed neutrinos have explicit bare mass terms in the Lagrangian and where these are dynamically generated through the mechanism of spontaneous symmetry breaking. We observe that for the first scenario, the scale at which the scalar potential becomes unstable is lower from that within the Standard Model. In addition the Yukawa couplings $\\mathbf{Y}_\

  14. Viscosity of colloidal suspensions

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, E.G.D. [Rockefeller Univ., New York, NY (United States); Schepper, I.M. de [Delft Univ. of Technology (Netherlands)

    1995-12-31

    Simple expressions are given for the effective Newtonian viscosity as a function of concentration as well as for the effective visco-elastic response as a function of concentration and imposed frequency, of monodisperse neutral colloidal suspensions over the entire fluid range. The basic physical mechanisms underlying these formulae are discussed. The agreement with existing experiments is very good.

  15. Effects of hydrophilic colloids on the stability of orange juice%亲水性胶体对橙汁饮料稳定性的影响

    Institute of Scientific and Technical Information of China (English)

    姚森; 王亮; 童彦

    2016-01-01

    Objective To study the effects of hydrophilic colloids such as gellan gum, xanthan gum and sodium alginate andetc. on the stability of 30% orange juice.MethodsThe significant factors that affected the stability of orange juice were screened by the U8(88) uniform design, and then the L9(34) orthogonal design was used to further optimize the best colloids compound.ResultsThe colloids of sodium alginate, gellan gum, pectin and xanthan gum had the most significant influence on orange juice precipitation, while guar gum, Arabic gum and carboxymethyl cellulose sodium (CMC) had no significant effect. Meanwhile, gellan gum and xanthan gum were conducive to turbid stability of orange juice, and xanthan gum and CMC could accelerate the flocculation of orange juice. The most important factors that affected the stability of orange juice were sodium alginate and gellen gum, which could inhibit precipitation and maintain turbid stability effectively when properly used. The main factor that accelerated flocculation was xanthan gum, however, suitable pectin and sodium alginate could prevent the formation of flocculation.ConclusionThe orange juices had the best stability with minimum precipitation or flocculation, and maximum turbid stability when adding 1.2‰ sodium alginate, 0.32‰ gellan gum and 0.8‰ pectin, respectively. The experiments conformed that under the best conditions, orange juice had good stability and no evident flocculation with the precipitation stability of 98.52% and the turbid stability of 94.89%.%目的:以30%橙汁饮料为对象,研究结冷胶、黄原胶、海藻酸钠等亲水性胶体对橙汁稳定性的影响。方法采用U8(88)均匀设计筛选出对橙汁稳定性影响最为显著的因素,再通过L9(34)正交设计进一步验证优化橙汁饮料中的胶体最佳复配方案。结果对橙汁沉淀影响最为显著的胶体是海藻酸钠、结冷胶、果胶、黄原胶,而瓜尔胶、阿拉伯胶和羧甲基纤维素钠(CMC)的

  16. Effects of hydrophilic colloids on the stability of orange juice%亲水性胶体对橙汁饮料稳定性的影响

    Institute of Scientific and Technical Information of China (English)

    姚森; 王亮; 童彦

    2016-01-01

    Objective To study the effects of hydrophilic colloids such as gellan gum, xanthan gum and sodium alginate and etc. on the stability of 30%orange juice. Methods The significant factors that affected the stability of orange juice were screened by the U8(88) uniform design, and then the L9(34) orthogonal design was used to further optimize the best colloids compound. Results The colloids of sodium alginate, gellan gum, pectin and xanthan gum had the most significant influence on orange juice precipitation, while guar gum, Arabic gum and carboxymethyl cellulose sodium (CMC) had no significant effect. Meanwhile, gellan gum and xanthan gum were conducive to turbid stability of orange juice, and xanthan gum and CMC could accelerate the flocculation of orange juice. The most important factors that affected the stability of orange juice were sodium alginate and gellen gum, which could inhibit precipitation and maintain turbid stability effectively when properly used. The main factor that accelerated flocculation was xanthan gum, however, suitable pectin and sodium alginate could prevent the formation of flocculation. Conclusion The orange juices had the best stability with minimum precipitation or flocculation, and maximum turbid stability when adding 1.2‰sodium alginate, 0.32‰gellan gum and 0.8‰pectin, respectively. The experiments conformed that under the best conditions, orange juice had good stability and no evident flocculation with the precipitation stability of 98.52%and the turbid stability of 94.89%.%目的:以30%橙汁饮料为对象,研究结冷胶、黄原胶、海藻酸钠等亲水性胶体对橙汁稳定性的影响。方法采用U8(88)均匀设计筛选出对橙汁稳定性影响最为显著的因素,再通过L9(34)正交设计进一步验证优化橙汁饮料中的胶体最佳复配方案。结果对橙汁沉淀影响最为显著的胶体是海藻酸钠、结冷胶、果胶、黄原胶,而瓜尔胶、阿拉伯胶和羧甲基纤维素钠(CMC)

  17. Enhanced stability and mechanical strength of sodium alginate composite films.

    Science.gov (United States)

    Liu, Sijun; Li, Yong; Li, Lin

    2017-03-15

    This work aims to study how three kinds of nanofillers: graphene oxide (GO), ammonia functionalized graphene oxide (AGO), and triethoxylpropylaminosilane functionalized silica, can affect stability and mechanical strength of sodium alginate (SA) composite films. The filler/sodium alginate (SA) solutions were first studied by rheology to reveal effects of various fillers on zero shear viscosity η0. SA composite films were then prepared by a solution mixing-evaporation method. The structure, morphology and properties of SA composite films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), contact angle and mechanical testing. Compared to GO and silica, the presence of AGO significantly improved the interaction between AGO and SA, which led to the increase in stability and mechanical strength of the resulting SA composite films. The tensile strength and elongation at break of AGO/SA composite film at 3wt% AGO loading were increased by 114.9% and 194.4%, respectively, in contrast to pure SA film. Furthermore, the stability of AGO/SA composite films at high temperatures and in a wet environment were better than that of silica/SA and GO/SA composite films. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. Stability as a natural selection mechanism on interacting networks

    Directory of Open Access Journals (Sweden)

    Francisco A. Tamarit

    2010-02-01

    Full Text Available Biological networks of interacting agents exhibit similar topological properties for a wide range of scales, from cellular to ecological levels, suggesting the existence of a common evolutionary origin. A general evolutionary mechanism based on global stability has been proposed recently  [J I Perotti, et al., Phys. Rev. Lett. 103, 108701 (2009]. This mechanism was incorporated into a  model of a growing network of interacting agents in which each new agent's membership in the network is determined by the agent's effect on the network's global stability. In this work, we analyze different quantities that characterize the topology of the emerging networks, such as global connectivity, clustering and average nearest neighbors degree, showing that they reproduce scaling behaviors frequently observed in several biological systems. The influence of the stability selection  mechanism on the dynamics associated to the resulting network, as well as  the interplay  between some topological and functional features are also analyzed.Received: 17 July 2010; Accepted: 27 September 2010; Edited by: D. H. Zanette; Reviewed by: V. M. Eguiluz, Inst. Fisica Interdisciplinar y Sist. Complejos, Palma de Mallorca, Spain; DOI: 10.4279/PIP.020005

  19. Electroweak vacuum stability and the seesaw mechanism revisited

    Energy Technology Data Exchange (ETDEWEB)

    Ng, J.N. [TRIUMF, Theory Department, Vancouver, BC (Canada); De la Puente, Alejandro [TRIUMF, Theory Department, Vancouver, BC (Canada); Carleton University, Department of Physics, Ottawa, ON (Canada)

    2016-03-15

    We study the electroweak vacuum stability in Type I seesaw models for three generations of neutrinos in scenarios where the right-handed neutrinos have explicit bare mass terms in the Lagrangian and where these are dynamically generated through the mechanism of spontaneous symmetry breaking. To best highlight the difference of the two cases we concentrate on the absolute stability of the scalar potential. We observe that for the first scenario, the scale at which the scalar potential becomes unstable is lower from that within the standard model. In addition the Yukawa couplings Y{sub ν} are constrained such that Tr[Y{sub ν}{sup †}Y{sub ν}] stability can be improved in a large region of parameter space. However, we found that the scalar used to break the lepton number symmetry cannot be too light and have a large coupling to right-handed neutrinos in order for the seesaw mechanism to be a valid mechanism for neutrino mass generation. In this case we have Tr[Y{sub ν}{sup †}Y{sub ν}]

  20. Characterization of colloidal silica abrasives with different sizes and their chemical–mechanical polishing performance on 4H-SiC (0 0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Xiaolei [The State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China); Shenzhen Key Laboratory of Micro/Nano Manufacturing, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057 (China); Pan, Guoshun, E-mail: pangs@tsinghua.edu.cn [The State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China); Shenzhen Key Laboratory of Micro/Nano Manufacturing, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057 (China); Zhou, Yan; Gu, Zhonghua; Gong, Hua; Zou, Chunli [The State Key Laboratory of Tribology, Tsinghua University, Beijing 100084 (China); Shenzhen Key Laboratory of Micro/Nano Manufacturing, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057 (China)

    2014-07-01

    In this paper, a detailed analysis is presented to characterize the performance of colloidal silica abrasives based slurry with different abrasive sizes on CMP of hexagonal 4H-SiC wafer, and indicates that the abrasive size is an important factor to determine the efficiency of CMP and the final planarization quality of wafer surface. The authors also present a detailed hypothesis to describe the material removal mechanism of 4H-SiC by colloidal silica abrasives during CMP process, and design two groups of experiments to demonstrate the rationality of the hypothesis. Furthermore, the authors put forward some suggestions to optimize the CMP efficiency and planarization quality of 4H-SiC wafer.

  1. Stability and Occurrence of the Molecule-Containing SiO2 Clathrate Melanophlogite: Metastable Crystallization from a Colloid or Gel?

    Science.gov (United States)

    Geiger, C. A.; Dachs, E.

    2008-12-01

    The mineral melanophlogite is the only known natural SiO2 clathrate. It has been found in a number of localities worldwide in different low-temperature geologic environments. Melanophlogite's thermodynamic stability is not known. Low-temperature hydrothermal laboratory experiments indicate that structure-directing agents and colloid formation are needed for crystallization. The formation of silica-rich colloids/gels and following crystal growth can be observed in glass-ampoule synthesis experiments. In order to better address these issues, the heat capacities of two different molecule-containing melanophlogites of approximate composition 46SiO2·1.80CH4·3.54N2·1.02CO2 from Mt. Hamilton, CA and 46SiO2·3.59CH4·3.10N2·1.31CO2 from Racalmuto, Sicily, along with a heated (molecule-free) sample of composition SiO2, were studied between 5 and 300 K using heat- pulse microcalorimetry. The molecule-free sample was obtained by heating a natural Racalmuto sample at 1173 K for 24 hr. It has a slightly larger low-temperature heat capacity and standard third-law entropy compared to other low-density SiO2 polymorphs such as various zeosils. The standard third-law entropy of the molecule-free sample is S° = 2216.3 J/(mol·K) for 46SiO2 and the natural Mt. Hamilton and Racalmuto samples give S° = 2805.7 J/(mol·K) and S° = 2956.8 J/(mol· K), respectively. The entropy and Gibbs free energy for molecule-free melanophlogite relative to quartz at 298 K are Δ Strans = 6.7 J/(mol·K) and Δ Gtrans = 7.5 kJ/mol, respectively and, thus, it does not have a thermodynamic field of stability in the SiO2 system. The difference in Cp values between molecule-containing and molecule-free melanophlogite is characterized by an increase in Cp from 0 K to approximately 70 K and then reaches a roughly constant value at 70 K cristobalite and chalcedony, suggest that melanophlogite crystallizes metastabily from gels. The occurrence of melanophlogite, and the lack of other SiO2clathrates

  2. Water dispersible CoFe{sub 2}O{sub 4} nanoparticles with improved colloidal stability for biomedical applications

    Energy Technology Data Exchange (ETDEWEB)

    Munjal, Sandeep [Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016 (India); Khare, Neeraj, E-mail: nkhare@physics.iitd.ernet.in [Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016 (India); Nehate, Chetan; Koul, Veena [Centre for Biomedical Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016 (India)

    2016-04-15

    Single phase cobalt ferrite (CoFe{sub 2}O{sub 4}, CFO) nanoparticles of a controlled size (∼6 nm) exhibiting superparamagnetic properties have been synthesized by hydrothermal technique using oleic acid (OA) as surfactant. The oleic acid coated CFO nanoparticles are stable in non-polar organic media, such as hexane but are not well dispersible in water. The surface of these nanoparticles has been further modified by citric acid using ligand exchange process, which makes CFO nanoparticles more stable colloidal solution in water. Citric acid coated CFO nanoparticles exhibits high dispersibility in water, high zeta potential, very low coercivity and moderate saturation magnetization. Biocompatibility of these CFO nanoparticles is demonstrated through cytotoxicity test in L929 cell line. - Highlights: • Synthesis of uniform size (~6nm) CoFe{sub 2}O{sub 4} (CFO) magnetic nano-particles, with a narrow size distribution using hydrothermal techniques with oleic acid as surfactant and convert the CFO nano-particles highly dispersible in water by modifying the surface of nanoparticles through ligand exchange process. • The bio-compatibility of these highly water dispersal citric acid coated CoFe{sub 2}O{sub 4} nanoparticles was demonstrated with mouse fibroblast L929 cells lines, using a MTT cytotoxicity assay. • The surface of these oleic acid coated nanoparticles was modified with citric acid using ligand exchange method, that makes these nanoparticles water highly dispersible. • The biocompatibility of citric acid coated CoFe{sub 2}O{sub 4} nanoparticles was demonstrated with mouse fibroblast L929 cells lines, using a MTT cytotoxicity assay.

  3. Effect of the Polymeric Stabilizer in the Aqueous Phase Fischer-Tropsch Synthesis Catalyzed by Colloidal Cobalt Nanocatalysts

    Directory of Open Access Journals (Sweden)

    Jorge A. Delgado

    2017-03-01

    Full Text Available A series of small and well defined cobalt nanoparticles were synthesized by the chemical reduction of cobalt salts in water using NaBH4 as a reducing agent and using various polymeric stabilizers. The obtained nanocatalysts of similar mean diameters (ca. 2.6 nm were fully characterized and tested in the aqueous phase Fischer-Tropsch Synthesis (AFTS. Interestingly, the nature and structure of the stabilizers used during the synthesis of the CoNPs affected the reduction degree of cobalt and the B-doping of these NPs and consequently, influenced the performance of these nanocatalysts in AFTS.

  4. Effect of the Polymeric Stabilizer in the Aqueous Phase Fischer-Tropsch Synthesis Catalyzed by Colloidal Cobalt Nanocatalysts

    Science.gov (United States)

    Delgado, Jorge A.; Claver, Carmen; Castillón, Sergio; Curulla-Ferré, Daniel; Godard, Cyril

    2017-01-01

    A series of small and well defined cobalt nanoparticles were synthesized by the chemical reduction of cobalt salts in water using NaBH4 as a reducing agent and using various polymeric stabilizers. The obtained nanocatalysts of similar mean diameters (ca. 2.6 nm) were fully characterized and tested in the aqueous phase Fischer-Tropsch Synthesis (AFTS). Interestingly, the nature and structure of the stabilizers used during the synthesis of the CoNPs affected the reduction degree of cobalt and the B-doping of these NPs and consequently, influenced the performance of these nanocatalysts in AFTS. PMID:28336892

  5. Raspberry Extract as Both a Stabilizer and a Reducing Agent in Environmentally Friendly Process of Receiving Colloidal Silver

    Directory of Open Access Journals (Sweden)

    Jolanta Pulit

    2013-01-01

    Full Text Available An ecofriendly method of nanosilver obtaining has been studied. The process involves the chemical reduction method carried out in aqueous environment. Silver nitrate (V was applied as a silver ions source. Raspberry extract was used as a natural source of both reducing and stabilizing agents. The total amount of phenolic compounds was determined by the Folin-Ciocalteu method. Obtained nanoparticles were analyzed by the dynamic light scattering technique so as to determine the particles size and suspension stability which was characterized by an electrokinetic potential. The results confirmed that the size of some nanoparticles was under 100 nm.

  6. Anisotropic Model Colloids

    Science.gov (United States)

    van Kats, C. M.

    2008-10-01

    The driving forces for fundamental research in colloid science are the ability to manage the material properties of colloids and to unravel the forces that play a role between colloids to be able to control and understand the processes where colloids play an important role. Therefore we are searching for colloidal materials with specific physical properties to better understand our surrounding world.Until recently research in colloid science was mainly focused on spherical (isotropic) particles. Monodisperse spherical colloids serve as a model system as they exhibit similar phase behaviour as molecular and atomic systems. Nevertheless, in many cases the spherical shape is not sufficient to reach the desired research goals. Recently the more complex synthesis methods of anisotropic model colloids has strongly developed. This thesis should be regarded as a contribution to this research area. Anisotropic colloids can be used as a building block for complex structures and are expected not only to lead to the construction of full photonic band gap materials. They will also serve as new, more realistic, models systems for their molecular analogues. Therefore the term ‘molecular colloids” is sometimes used to qualify these anisotropic colloidal particles. In the introduction of this thesis, we give an overview of the main synthesis techniques for anisotropic colloids. Chapter 2 describes the method of etching silicon wafers to construct monodisperse silicon rods. They subsequently were oxidized and labeled (coated) with a fluorescent silica layer. The first explorative phase behaviour of these silica rods was studied. The particles showed a nematic ordering in charge stabilized suspensions. Chapter 3 describes the synthesis of colloidal gold rods and the (mesoporous) silica coating of gold rods. Chapter 4 describes the physical and optical properties of these particles when thermal energy is added. This is compared to the case where the particles are irradiated with

  7. Oil-in-water Pickering emulsions stabilized by colloidal particles from the water-insoluble protein zein

    NARCIS (Netherlands)

    de Folter, J.W.J.; van Ruijven, M.W.M.; Velikov, K.

    2012-01-01

    Few fully natural and biocompatible materials are available for the effective particle-stabilization of emulsions since strict requirements, such as insolubility in both fluid phases and intermediate wettability, need to be met. In this paper, we demonstrate the first use of water-insoluble proteins

  8. Invaded grassland communities have altered stability-maintenance mechanisms but equal stability compared to native communities.

    Science.gov (United States)

    Wilsey, Brian J; Daneshgar, Pedram P; Hofmockel, Kirsten; Polley, H Wayne

    2014-01-01

    Theory predicts that stability should increase with diversity via several mechanisms. We tested predictions in a 5-year experiment that compared low-diversity exotic to high-diversity native plant mixtures under two irrigation treatments. The study included both wet and dry years. Variation in biomass across years (CV) was 50% lower in mixtures than monocultures of both native and exotic species. Growth among species was more asynchronous and overyielding values were greater during and after a drought in native than exotic mixtures. Mean-variance slopes indicated strong portfolio effects in both community types, but the intercept was higher for exotics than for natives, suggesting that exotics were inherently more variable than native species. However, this failed to result in higher CV's in exotic communities because species that heavily dominated plots tended to have lower than expected variance. Results indicate that diversity-stability mechanisms are altered in invaded systems compared to native ones they replaced.

  9. Colloidal nematostatics

    Directory of Open Access Journals (Sweden)

    V.M. Pergamenshchik

    2010-01-01

    Full Text Available We give a review of the theory of large distance colloidal interaction via the nematic director field. The new area of nematic colloidal systems (or nematic emulsions has been guided by the analogy between the colloidal nematostatics and electrostatics. The elastic charge density representation of the colloidal nematostatics [V.M. Pergamenshchik, V.O. Uzunova, Eur. Phys. J. E, 2007, 23, 161; Phys. Rev. E, 2007, 76, 011707] develops this analogy at the level of charge density and Coulomb interaction. The analogy is shown to lie in common mathematics based on the solutions of Laplace equation. However, the 3d colloidal nematostatics substantially differs from electrostatics both in its mathematical structure and physical implications. The elastic charge is a vector fully determined by the torque exerted upon colloid, the role of Gauss' theorem is played by conservation of the torque components. Elastic multipoles consist of two tensors (dyads. Formulas for the elastic multipoles, the Coulomb-like, dipole-dipole, and quadrupole-quadrupole pair interaction potentials are derived and illustrated by particular examples. Based on the tensorial structure, we list possible types of elastic dipoles and quadrupoles. An elastic dipole is characterized by its isotropic strength, anisotropy, chirality, and its longitudinal component. An elastic quadrupole can be uniaxial and biaxial. Relation between the multipole type and its symmetry is discussed, sketches of some types of multipoles are given. Using the mirror image method of electrostatics as a guiding idea, we develop the mirror image method in nematostatics for arbitrary director tilt at the wall. The method is applied to the charge-wall and dipole-wall interaction.

  10. The effect of gold colloid on the fluorescence spectrum from Safranine T: a physical mechanism based on resonance light scattering.

    Science.gov (United States)

    Li, Jianjun; Zhu, Jian; Zhao, Junwu

    2011-05-01

    The non-monotonic change of fluorescence intensity from Safranine T was observed experimentally by adding gold colloids to the Safranine T aqueous solution. Increasing the content of gold colloids leads to the fluorescence emission peak red shift and increases first and then decreases. We believe that one of the important reasons of the fluorescence changing and shifting is due to the resonance light scattering from gold nanoparticles which is stimulated by the fluorescence of Safranine T and is tunable by the shell thickness of the ST that coated around the gold particles.

  11. Freezing of Charge-stabilized Colloidal Dispersions%电荷稳定的胶体分散体的凝固

    Institute of Scientific and Technical Information of China (English)

    周世琦

    2003-01-01

    Rogers-Young approximation for Ornstein-Zernike integral equation is com-bined with Hansen-Verlet one phase criterion for freezing to predict freezing of hard core re-pulsive Yukawa model ( HCRYM ) fluid. Comparison of theoretical predictions with corre-sponding computer simulation data uncloses the superiority of the Rogers-Young approxima-tion over Hypemetted chain approximation and rescaled mean spherical approximation forfreezing. Then, the Rogers-Young approximation combined with the Hansen-Verlet one phasecriterion is employed for the freezing of many-component charge-stabilized colloidal disper-sions, which consist of colloidal macro-ions, electrolyte small ions and solvent molecules, andare modeled as a single-component charged hard core macro-ion interacting through ascreened Coulomb potential. The theoretically predicted freezing line with the macro-ion sur-face charge number being assumed as an adjustable parameter is in very good agreement withthe corresponding experimental data. The reason why by the empirical Hansen-Verlet struc-ture function approach,the single-component coarse-grained effective potential is valid for thefreezing description of the many-component charge-stabilized colloidal solutions, but not validfor the case of asymmetric binary hard sphere mixtures, is discussed.%Rogers-Young近似结合ornstein-Zernike积分方程与Hansen-Verlet单相凝固标准预言硬核排斥汤川模型流体的凝固.理论预言与相应的计算机模拟数据的比较揭示了Rogers-Young近似比超网链近似与重标度平均球形近似精度高.在此基础上,Rogers-Young近似结合Hansen-Verlet单相凝固标准预言多组分电荷稳定的胶体分散体的凝固,胶体分散体由胶体大离子、电解质小离子和溶剂分子组成,用单组分荷电硬核大离子(由屏蔽库伦相互作用势描述)来模拟.当荷电硬核大离子的表面电荷被当作可调参数时,所预言的凝固线与相应的实验数据符合很好.讨

  12. Mechanical stability of end-linked polymer gel

    Energy Technology Data Exchange (ETDEWEB)

    Roy Majumder, Shashwati [Theoretical Chemistry Section, Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India); Bandyopadhyay, Tusar [Theoretical Chemistry Section, Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)]. E-mail: btusar@barc.ernet.in; Ghosh, Swapan K. [Theoretical Chemistry Section, Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085 (India)

    2005-11-01

    The mechanical stability of end-linked polymer network (gel) at large deformation has been studied with the aid of a simplified model. The model consists of square network of end-linked Hookean spring, each representing an ideal polymer chain. To mimic the structure prevailing at the gel point, the square network of springs was self-similarly repeated to generate a deterministic fractal structure having fractal dimensions, d{sub f}=1.56-1.8. For any given d{sub f}, the distribution of pores (measured by lacunarity of the network) in the structure also serves as an important parameter that characterizes the morphology of the network. Our preliminary results show that the present minimalist model qualitatively reproduces the non-monotonous structure-stability relationship, as observed in radiation-induced cross-linked polymer networks. Structures with highest lacunarity for a given fractal network have also been found to exhibit highest mechanical stability against an external deforming force before it is finally crumpled and found to form a wrinkled network.

  13. Stabilization and set-point regulation of underactuated mechanical systems

    Science.gov (United States)

    Loccufier, Mia

    2016-09-01

    Mechanical systems are referred to as underactuated if the number of independent actuators are fewer than the number of degrees of freedom, a general encountered problem in engineering applications. The considered mechanical systems belong to the class of Euler- Lagrange systems where both kinetic energy and potential energy are modeled in their most general form and energy dissipation is modeled according to the dissipation function of Rayleigh, i.e. viscous damping forces are assumed. The control objectives are stabilization and set-point regulation. The structure of the controller is a parallel combination of static output feedback with dynamic output feedback where nonlinear amplifiers are included. An energy based approach with Liapunov functions and the Kalman-Yacubovich-Popov main lemma yields alternative stability theorems. A number of conditions are introduced with respect to the controller's structure in order to guarantee stability. However, sufficient design freedom is left to choose a proper tuning principle and obtain the specified control objectives such as fast convergence to a set-point combined with disturbance rejection. A restriction on the control input energy can be incorporated as well. The applicability of the method will be illustrated with planar manipulators. The main contribution is that a methodology is developed which incorporates many controllers and tuning facilities.

  14. Colloid-Facilitated Transport of Low-Solubility Radionuclides: A Field, Experimental, and Modeling Investigation

    Energy Technology Data Exchange (ETDEWEB)

    Kersting, A B; Reimus, P W; Abdel-Fattah, A; Allen, P G; Anghel, I; Benedict, F C; Esser, B K; Lu, N; Kung, K S; Nelson, J; Neu, M P; Reilly, S D; Smith, D K; Sylwester, E R; Wang, L; Ware, S D; Warren, RG; Williams, R W; Zavarin, M; Zhao, P

    2003-02-01

    For the last several years, the Underground Test Area (UGTA) program has funded a series of studies carried out by scientists to investigate the role of colloids in facilitating the transport of low-solubility radionuclides in groundwater, specifically plutonium (Pu). Although the studies were carried out independently, the overarching goals of these studies has been to determine if colloids in groundwater at the NTS can and will transport low-solubility radionuclides such as Pu, define the geochemical mechanisms under which this may or may not occur, determine the hydrologic parameters that may or may not enhance transport through fractures and provide recommendations for incorporating this information into future modeling efforts. The initial motivation for this work came from the observation in 1997 and 1998 by scientists from Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL) that low levels of Pu originally from the Benham underground nuclear test were detected in groundwater from two different aquifers collected from wells 1.3 km downgradient (Kersting et al., 1999). Greater than 90% of the Pu and other radionuclides were associated with the naturally occurring colloidal fraction (< 1 micron particles) in the groundwater. The colloids consisted mainly of zeolite (mordenite, clinoptilolite/heulandite), clays (illite, smectite) and cristobalite (SiO{sub 2}). These minerals were also identified as alteration mineral components in the host rock aquifer, a rhyolitic tuff. The observation that Pu can and has migrated in the subsurface at the NTS has forced a rethinking of our basic assumptions regarding the mechanical and geochemical transport pathways of low-solubility radionuclides. If colloid-facilitated transport is the primary mechanism for transporting low-solubility radionuclides in the subsurface, then current transport models based solely on solubility arguments and retardation estimates may underestimate the flux and

  15. Analysis of Stability and Bifurcation in Nonlinear Mechanics with Dissipation

    Directory of Open Access Journals (Sweden)

    Claude Stolz

    2011-01-01

    Full Text Available The analysis of stability and bifurcation is studied in nonlinear mechanics with dissipative mechanisms: plasticity, damage, fracture. The description is based on introduction of a set of internal variables. This framework allows a systematic description of the material behaviour via two potentials: the free energy and the potential of dissipation. In the framework of standard generalized materials the internal state evolution is governed by a variational inequality which depends on the mechanism of dissipation. This inequality is obtained through energetic considerations in an unified description based upon energy and driving forces associated to the dissipative process. This formulation provides criterion for existence and uniqueness of the system evolution. Examples are presented for plasticity, fracture and for damaged materials.

  16. Moving Constraints as Stabilizing Controls in Classical Mechanics

    Science.gov (United States)

    Bressan, Alberto; Rampazzo, Franco

    2010-04-01

    The paper analyzes a Lagrangian system which is controlled by directly assigning some of the coordinates as functions of time, by means of frictionless constraints. In a natural system of coordinates, the equations of motion contain terms which are linear or quadratic with respect to time derivatives of the control functions. After reviewing the basic equations, we explain the significance of the quadratic terms related to geodesics orthogonal to a given foliation. We then study the problem of stabilization of the system to a given point by means of oscillating controls. This problem is first reduced to theweak stability for a related convex-valued differential inclusion, then studied by Lyapunov functions methods. In the last sections, we illustrate the results by means of various mechanical examples.

  17. Moving constraints as stabilizing controls in classical mechanics

    CERN Document Server

    Bressan, A

    2008-01-01

    The paper analyzes a Lagrangian system which is controlled by directly assigning some of the coordinates as functions of time, by means of frictionless constraints. In a natural system of coordinates, the equations of motions contain terms which are linear or quadratic w.r.t.time derivatives of the control functions. After reviewing the basic equations, we explain the significance of the quadratic terms, related to geodesics orthogonal to a given foliation. We then study the problem of stabilization of the system to a given point, by means of oscillating controls. This problem is first reduced to the weak stability for a related convex-valued differential inclusion, then studied by Lyapunov functions methods. In the last sections, we illustrate the results by means of various mechanical examples.

  18. Synthesis and Characterization of Supramolecular Colloids.

    Science.gov (United States)

    Vilanova, Neus; De Feijter, Isja; Voets, Ilja K

    2016-04-22

    Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

  19. Mechanism of protein kinetic stabilization by engineered disulfide crosslinks.

    Directory of Open Access Journals (Sweden)

    Inmaculada Sanchez-Romero

    Full Text Available The impact of disulfide bonds on protein stability goes beyond simple equilibrium thermodynamics effects associated with the conformational entropy of the unfolded state. Indeed, disulfide crosslinks may play a role in the prevention of dysfunctional association and strongly affect the rates of irreversible enzyme inactivation, highly relevant in biotechnological applications. While these kinetic-stability effects remain poorly understood, by analogy with proposed mechanisms for processes of protein aggregation and fibrillogenesis, we propose that they may be determined by the properties of sparsely-populated, partially-unfolded intermediates. Here we report the successful design, on the basis of high temperature molecular-dynamics simulations, of six thermodynamically and kinetically stabilized variants of phytase from Citrobacter braakii (a biotechnologically important enzyme with one, two or three engineered disulfides. Activity measurements and 3D crystal structure determination demonstrate that the engineered crosslinks do not cause dramatic alterations in the native structure. The inactivation kinetics for all the variants displays a strongly non-Arrhenius temperature dependence, with the time-scale for the irreversible denaturation process reaching a minimum at a given temperature within the range of the denaturation transition. We show this striking feature to be a signature of a key role played by a partially unfolded, intermediate state/ensemble. Energetic and mutational analyses confirm that the intermediate is highly unfolded (akin to a proposed critical intermediate in the misfolding of the prion protein, a result that explains the observed kinetic stabilization. Our results provide a rationale for the kinetic-stability consequences of disulfide-crosslink engineering and an experimental methodology to arrive at energetic/structural descriptions of the sparsely populated and elusive intermediates that play key roles in irreversible

  20. The stabilizing mechanism of the Latarjet procedure: a cadaveric study.

    Science.gov (United States)

    Yamamoto, Nobuyuki; Muraki, Takayuki; An, Kai-Nan; Sperling, John W; Cofield, Robert H; Itoi, Eiji; Walch, Gilles; Steinmann, Scott P

    2013-08-07

    The Latarjet procedure has been used commonly for extra-articular treatment of anterior glenohumeral joint instability. Recently, the technique also has been used as a bone-grafting procedure to repair large glenoid defects. The "sling effect" and the "bone-block effect" have been proposed as the stabilizing mechanisms of this procedure. The aim of this study was to determine the stabilizing mechanisms of this procedure. Eight fresh-frozen shoulders were prepared and tested with use of a custom testing machine instrumented with a load cell. With a 50-N axial force applied to the humerus, the humeral head was translated anteriorly. Translational force was measured at both the end-range and the mid-range arm positions, with the capsule intact, after creation of a Bankart lesion, after creation of a large glenoid defect, and after the Latarjet procedure with no load and then three different sets of loads applied to the subscapularis and conjoint tendons. Then, these two tendons were removed to observe the contribution of the sling effect to the stability. Finally, the sutures attaching the coracoacromial ligament to the capsular flap were removed in order to observe the effect of that attachment. The translational force, which decreased significantly after creation of a Bankart lesion or a large glenoid defect, returned to the intact-condition level after the Latarjet procedure was performed. At the end-range arm position, the contribution of the sling effect by the subscapularis and conjoint tendons was 76% to 77% as the load changed, and the remaining 23% to 24% was contributed by the suturing of the capsular flap. At the mid-range position, the contribution of the sling effect was 51% to 62%, and the remaining 38% to 49% was contributed by the reconstruction of the glenoid. The main stabilizing mechanism of the Latarjet procedure was the sling effect at both the end-range and the mid-range arm positions. The Latarjet procedure remains an effective procedure for

  1. Colloidal superballs

    NARCIS (Netherlands)

    Rossi, L.

    2012-01-01

    This thesis is organized in four parts as follows. Part 1 focuses on the synthetic aspects of the colloidal model systems that will be used throughout the work described in this thesis. In Chapter 2 we describe synthetic procedures for the preparation of polycrystalline hematite superballs and super

  2. The influence of cilica gel on wheat beer colloidal stabilization%硅胶处理对小麦啤酒胶体稳定性的影响

    Institute of Scientific and Technical Information of China (English)

    王海明; 余功德; 朱景林

    2001-01-01

    The aim was to discover the influence of cilica gel on wheat beercolloidal stabilization. In comparison with normal beer, wheat beer has poor colloidal stabilization, especially when stored in refrigerator, it tends to generate chill haze due to the higher concentration of protein from wheat malt which used as main brewing material. Shelf-life can been predicted by SASPL test and hot/cold cycle forcing test. We found that treatment with silica gel in the cold conditioning process could effectively prolong shelf-life of wheat beer .%表明硅胶处理对小麦啤酒胶体稳定性的影响。小麦啤酒与正常的啤酒相比,小麦啤酒的抗冷能力较差,尤其是啤酒在冰箱内保藏温度接近0℃时,啤酒容易出现冷混浊,这是由于用于酿造小麦啤酒的主要原料小麦麦芽含有较高的蛋白质。我们通过在贮酒后期添加硅胶,将成品啤酒经饱和硫酸铵极限试验和冷热试验测定啤酒的SASPL值和保质期,发现使用硅胶可以有效地延长小麦啤酒的保质期。

  3. Vacancy-induced mechanical stabilization of cubic tungsten nitride

    Science.gov (United States)

    Balasubramanian, Karthik; Khare, Sanjay; Gall, Daniel

    2016-11-01

    First-principles methods are employed to determine the structural, mechanical, and thermodynamic reasons for the experimentally reported cubic WN phase. The defect-free rocksalt phase is both mechanically and thermodynamically unstable, with a negative single crystal shear modulus C44=-86 GPa and a positive enthalpy of formation per formula unit Hf=0.623 eV with respect to molecular nitrogen and metallic W. In contrast, WN in the NbO phase is stable, with C44=175 GPa and Hf=-0.839 eV . A charge distribution analysis reveals that the application of shear strain along [100] in rocksalt WN results in an increased overlap of the t2 g orbitals which causes electron migration from the expanded to the shortened W-W bond axes, yielding a negative shear modulus due to an energy reduction associated with new bonding states 8.1-8.7 eV below the Fermi level. A corresponding shear strain in WN in the NbO phase results in an energy increase and a positive shear modulus. The mechanical stability transition from the NaCl to the NbO phase is explored using supercell calculations of the NaCl structure containing Cv=0 %-25 % cation and anion vacancies, while keeping the N-to-W ratio constant at unity. The structure is mechanically unstable for Cvconcentration, the isotropic elastic modulus E of cubic WN is zero, but increases steeply to E =445 GPa for Cv=10 % , and then less steeply to E =561 GPa for Cv=25 % . Correspondingly, the hardness estimated using Tian's model increases from 0 to 15 to 26 GPa as Cv increases from 5% to 10% to 25%, indicating that a relatively small vacancy concentration stabilizes the cubic WN phase and that the large variations in reported mechanical properties of WN can be attributed to relatively small changes in Cv.

  4. The ZX-calculus is complete for stabilizer quantum mechanics

    Science.gov (United States)

    Backens, Miriam

    2014-09-01

    The ZX-calculus is a graphical calculus for reasoning about quantum systems and processes. It is known to be universal for pure state qubit quantum mechanics (QM), meaning any pure state, unitary operation and post-selected pure projective measurement can be expressed in the ZX-calculus. The calculus is also sound, i.e. any equality that can be derived graphically can also be derived using matrix mechanics. Here, we show that the ZX-calculus is complete for pure qubit stabilizer QM, meaning any equality that can be derived using matrices can also be derived pictorially. The proof relies on bringing diagrams into a normal form based on graph states and local Clifford operations.

  5. Interplay between Colloids and Interfaces : Emulsions, Foams and Microtubes

    NARCIS (Netherlands)

    de Folter, J.W.J.

    2013-01-01

    The central theme of this thesis is the interplay between colloids and interfaces. The adsorption of colloids at fluid-fluid interfaces is the main topic and covers Chapters 2-6. Pickering emulsions where colloidal particles act as emulsion stabilizers in the absence of surfactants are studied in a

  6. Evidence that Clostridium perfringens theta-toxin induces colloid-osmotic lysis of erythrocytes.

    OpenAIRE

    Harris, R W; Sims, P J; Tweten, R K

    1991-01-01

    Clostridium perfringens theta-toxin was shown to lyse target erythrocytes by a colloid-osmotic mechanism. Analysis showed the onset of lysis of erythrocytes by theta-toxin could be temporarily stabilized with 0.3 M sucrose. Flow cytometry analysis of the size distribution of theta-toxin-treated erythrocytes showed swelling of the erythrocytes prior to lysis.

  7. Mechanical properties and stabilities of α-boron monolayers.

    Science.gov (United States)

    Peng, Qing; Han, Liang; Wen, Xiaodong; Liu, Sheng; Chen, Zhongfang; Lian, Jie; De, Suvranu

    2015-01-21

    We investigate the mechanical properties and stabilities of planar α-boron monolayers under various large strains using density functional theory (DFT). α-Boron has a high in-plane stiffness, about 2/3 of that of graphene, which suggests that α-boron is four times as strong as iron. Potential profiles and stress-strain curves indicate that a free standing α-boron monolayer can sustain large tensile strains, up to 0.12, 0.16, and 0.18 for armchair, zigzag, and biaxial deformations, respectively. Third, fourth, and fifth order elastic constants are indispensable for accurate modeling of the mechanical properties under strains larger than 0.02, 0.06, and 0.08 respectively. Second order elastic constants, including in-plane stiffness, are predicted to monotonically increase with pressure, while the trend of Poisson's ratio is reversed. The surface sound speeds of both the compressional and shear waves increase with pressure. The ratio of these two sound speeds increases with the increase of pressure and converges to a value of 2.5. Our results imply that α-boron monolayers are mechanically stable under various large strains and have advanced mechanical properties - high strength and high flexibility.

  8. What happens when pharmaceuticals meet colloids.

    Science.gov (United States)

    Xing, Yingna; Chen, Xijuan; Zhuang, Jie; Chen, Xin

    2015-12-01

    Pharmaceuticals (PCs) have been widely detected in natural environment due to agricultural application of reclaimed water, sludge and animal wastes. Their potential risks to various ecosystems and even to human health have caused great concern; however, little was known about their environmental behaviors. Colloids (such as clays, metal oxides, and particulate organics) are kind of substances that are active and widespread in the environment. When PCs meet colloids, their interaction may influence the fate, transport, and toxicity of PCs. This review summarizes the progress of studies on the role of colloids in mediating the environmental behaviors of PCs. Synthesized results showed that colloids can adsorb PCs mainly through ion exchange, complexation and non-electrostatic interactions. During this process the structure of colloids and the stability of PCs may be changed. The adsorbed PCs may have higher risks to induce antibiotic resistance; besides, their transport may also be altered considering they have great chance to move with colloids. Solution conditions (such as pH, ionic strength, and cations) could influence these interactions between PCs and colloids, as they can change the forms of PCs and alter the primary forces between PCs and colloids in the solution. It could be concluded that PCs in natural soils could bind with colloids and then co-transport during the processes of irrigation, leaching, and erosion. Therefore, colloid-PC interactions need to be understood for risk assessment of PCs and the best management practices of various ecosystems (such as agricultural and wetland systems).

  9. Interactions of dissolved organic matter with natural and engineered inorganic colloids: a review.

    Science.gov (United States)

    Philippe, Allan; Schaumann, Gabriele E

    2014-08-19

    This contribution critically reviews the state of knowledge on interactions of natural colloids and engineered nanoparticles with natural dissolved organic materials (DOM). These interactions determine the behavior and impact of colloids in natural system. Humic substances, polysaccharides, and proteins present in natural waters adsorb onto the surface of most colloids. We outline major adsorption mechanisms and structures of adsorption layers reported in the literature and discuss their generality on the basis of particle type, DOM type, and media composition. Advanced characterization methods of both DOM and colloids are needed to address insufficiently understood aspects as DOM fractionation upon adsorption, adsorption reversibility, and effect of capping agent. Precise knowledge on adsorption layer helps in predicting the colloidal stability of the sorbent. While humic substances tend to decrease aggregation and deposition through electrostatic and steric effects, bridging-flocculation can occur in the presence of multivalent cations. In the presence of DOM, aggregation may become reversible and aggregate structure dynamic. Nonetheless, the role of shear forces is still poorly understood. If traditional approaches based on the DLVO-theory can be useful in specific cases, quantitative aggregation models taking into account DOM dynamics, bridging, and disaggregation are needed for a comprehensive modeling of colloids stability in natural media.

  10. Light-structured colloidal assemblies

    Science.gov (United States)

    Aubret, Antoine; Mena, Youssef; Ramananarivo, Sophie; Sacanna, Stefano; Palacci, Jeremie; Palacci lab Team; Sacanna lab Team

    2016-11-01

    Self-propelled particles (SPP) are a key tool since they are of relative simplicity as compared to biological micro-entities and provide a higher level of control. They can convert an energy source into motion and work, and exhibit surprising non-equilibrium behavior. In our work, we focus on the manipulation of colloids using light. We exploit osmotic and phoretic effects to act on single and ensemble of colloids. The key mechanism relies on the photocatalytic decomposition of hydrogen peroxide using hematite, which triggers the motion of colloids around it when illuminated. We use hematite particles and particles with photocatalytic inclusions (i.e. SPP). We first show that the interactions between hematite and colloidal tracers can be tuned by adjusting the chemical environment. Furthermore, we report a phototaxic behavior (migration in light gradient) of the particles. From this, we explore the effect of spatio-temporal modulation of the light to control the motion of colloids at the single particle level, and to generate self-assembled colloidal structures through time and space. The so-formed structures are maintained by phoretic and hydrodynamic forces resulting from the motion of each particles. Ultimately, a dynamic light modulation may be a route for the creation of active colloidal motion on a collective scale through the synchronization of the individual motions of SPP. This work is supported by NSF CAREER DMR 1554724.

  11. TiO/sub 2/ and CdS colloids stabilized by. beta. -cyclodextrins: tailored semiconductor-receptor systems as a means to control interfacial electron-transfer processes

    Energy Technology Data Exchange (ETDEWEB)

    Willner, I.; Eichen, Y.

    1987-10-28

    The photocatalytic activity of semiconductor particles is of substantial interest in synthesis as well as a means of solar energy conversion and storage. Electron-transfer reactions such as charge ejection or charge injection at semiconductor - solution interfaces are important factors that control the photocatalytic activity of the semiconductors. Electrostatic attraction of solute to the semiconductor surface has improved charge ejection from the excited semiconductor to solute relays. Adsorption of dyes to the semiconductor surface, i.e., by hydrophobic interactions, resulted in effective charge injection to the semiconductor and consequently the photocatalytic activity of semiconductors operative in the UV region could be shifted to the visible absorption spectrum. Substantial efforts have also been directed in recent years toward the preparation of semiconductor particles in colloidal forms to improve their light harvesting and interfacial electron-transfer properties. Stabilization of semiconductor colloids by polymers, microemulsions, and vesicle encapsulation has been reported. Here they report on a novel method for stabilizing semiconductor colloids by ..beta..-cyclodextrin (..beta..-CD).

  12. Biocompatible and colloidally stabilized mPEG-PE/calcium phosphate hybrid nanoparticles loaded with siRNAs targeting tumors.

    Science.gov (United States)

    Gao, Pei; Zhang, Xiangyu; Wang, Hongzhi; Zhang, Qinghong; Li, He; Li, Yaogang; Duan, Yourong

    2016-01-19

    Calcium phosphate nanoparticles are safe and effective delivery vehicles for small interfering RNA (siRNA), as a result of their excellent biocompatibility. In this work, mPEG-PE (polyethylene glycol-L-α-phosphatidylethanolamine) was synthesized and used to prepare nanoparticles composed of mPEG-PE and calcium phosphate for siRNA delivery. Calcium phosphate and mPEG-PE formed the stable hybrid nanoparticles through self-assembly resulting from electrostatic interaction in water. The average size of the hybrid nanoparticles was approximately 53.2 nm with a negative charge of approximately -16.7 mV, which was confirmed by dynamic light scattering (DLS) measurements. The nanoparticles exhibited excellent stability in serum and could protect siRNA from ribonuclease (RNase) degradation. The cellular internalization of siRNA-loaded nanoparticles was evaluated in SMMC-7721 cells using a laser scanning confocal microscope (CLSM) and flow cytometry. The hybrid nanoparticles could efficiently deliver siRNA to cells compared with free siRNA. Moreover, the in vivo distribution of Cy5-siRNA-loaded hybrid nanoparticles was observed after being injected into tumor-bearing nude mice. The nanoparticles concentrated in the tumor regions through an enhanced permeability and retention (EPR) effect based on the fluorescence intensities of tissue distribution. A safety evaluation of the nanoparticles was performed both in vitro and in vivo demonstrating that the hybrid nanoparticle delivery system had almost no toxicity. These results indicated that the mPEG-PE/CaP hybrid nanoparticles could be a stable, safe and promising siRNA nanocarrier for anticancer therapy.

  13. Crystallization and colloidal stabilization of Ca(OH)2 in the presence of nopal juice (Opuntia ficus indica): Implications in architectural heritage conservation.

    Science.gov (United States)

    Rodriguez-Navarro, Carlos; Ruiz-Agudo, Encarnacion; Burgos-Cara, Alejandro; Elert, Kerstin; Hansen, Eric F

    2017-09-20

    Hydrated lime (Ca(OH)2) is a vernacular art and building material produced following slaking of CaO in water. If excess water is used, a slurry, called lime putty forms, which has been the preferred craftsman selection for formulating lime mortars since Roman times. A variety of natural additives were traditionally added to the lime putty to improve its quality. The mucilaginous juice extracted from nopal cladodes has been and still is used as additive incorporated in the slaking water for formulation of lime mortars and plasters both in ancient Mesoamerica as well as in the USA Southwest. Little is known on the ultimate effects of this additive on the crystallization and microstructure of hydrated lime. Here, we show that significant changes in habit and size of portlandite crystals occur following slaking in the presence of nopal juice as well as compositionally-similar citrus pectin. Both additives contain polysaccharides made up of galacturonic acid and neutral sugar residues. The carboxyl (and hydroxyl) functional groups present in these residues and in their alkaline degradation by-products, which are deprotonated at the high pH (12.4) produced during lime slaking, strongly interact with newly formed Ca(OH)2 crystals acting in two ways: a) as nucleation inhibitors, promoting the formation of nanosized crystals, and b) as habit modifiers, favoring the development of planar habit following their adsorption onto positively charged (0001)Ca(OH)2 faces. Adsorption of polysaccharides on Ca(OH)2 crystals prevents the development of large particles, resulting in a very reactive, nanosized portlandite slurry. It also promotes steric stabilization, which limits aggregation, thus enhancing the colloidal nature of the lime putty. Overall, these effects are very favorable for the preparation of highly plastic lime mortars with enhanced properties.

  14. Colloidal Stability and Magnetic Field-Induced Ordering of Magnetorheological Fluids Studied with a Quartz Crystal Microbalance

    Directory of Open Access Journals (Sweden)

    Jaime Rodriguez-López

    2015-12-01

    Full Text Available This work proposes the use of quartz crystal microbalances (QCMs as a method to analyze and characterize magnetorheological (MR fluids. QCM devices are sensitive to changes in mass, surface interactions, and viscoelastic properties of the medium contacting its surface. These features make the QCM suitable to study MR fluids and their response to variable environmental conditions. MR fluids change their structure and viscoelastic properties under the action of an external magnetic field, this change being determined by the particle volume fraction, the magnetic field strength, and the presence of thixotropic agents among other factors. In this work, the measurement of the resonance parameters (resonance frequency and dissipation factor of a QCM are used to analyze the behavior of MR fluids in static conditions (that is, in the absence of external mechanical stresses. The influence of sedimentation under gravity and the application of magnetic fields on the shifts of resonance frequency and dissipation factor were measured and discussed in the frame of the coupled resonance produced by particles touching the QCM surface. Furthermore, the MR-fluid/QCM system has a great potential for the study of high-frequency contact mechanics because the translational and rotational stiffness of the link between the surface and the particles can be tuned by the magnetic field.

  15. Soil colloidal behavior

    Science.gov (United States)

    Recent understanding that organic and inorganic contaminants are often transported via colloidal particles has increased interest in colloid science. The primary importance of colloids in soil science stems from their surface reactivity and charge characteristics. Characterizations of size, shape,...

  16. Mechanisms of nitrogen heterocycle influence on turbine fuel stability

    Science.gov (United States)

    Daniel, S. R.; Worstell, J. H.

    1980-01-01

    Lewis bases were extracted from a Utah COED syncrude via ligand exchange. Addition of this extract to Jet A at levels as low as 5 ppm N produced deterioration of stability in both JFTOT and accelerated storage tests (7 days at 394 K with 13:1air to fuel ratio). Comparable effects on Jet A stability were obtained by addition of pyridine and quinoline, while pyrrole and indole were less detrimental at the same concentration level. The weight of deposit produced accelerated storage tests was found to be proportional to the concentration of added nitrogen compound. Over the narrow temperature range accessible with the experimental method, Arrhenius plots obtained by assuming specific rate to be proportional to the weight of material deposited in seven days exhibit greater slopes in the presence of those nitrogen compounds producing the greater deposition rates. It is shown that despite variation in appearance the elemental composition and spectral characteristics of the deposits are unaffected by addition of the nitrogen compounds. The linearity of the Arrhenius plots and of a plot of Arrhenius slope versus intercept for all the compounds suggests a constancy of mechanism over the range of temperature and heterocycles studied.

  17. Degradation mechanism and stability of 5-aminolevulinic acid.

    Science.gov (United States)

    Bunke, A; Zerbe, O; Schmid, H; Burmeister, G; Merkle, H P; Gander, B

    2000-10-01

    The physiological substance and precursor of the heme synthesis 5-aminolevulinic acid (ALA) is a promising prodrug for photodiagnosis and photodynamic therapy of epithelial tumors, particularly in urological and gynecological tissues. For the clinical use of this substance, a chemically stable and sterile drug formulation is required. In the present study, degradation mechanism of ALA in aqueous solution and possibilities to improve its stability were examined. A capillary electrophoretic method was developed that was suitable for the quantification of ALA and of two degradation products. The intermediate degradation product was 2, 5-dicarboxyethyl-3,6-dihydropyrazine, which was further oxidized to 2,5-dicarboxyethylpyrazine. The structures of the degradation products were proven by (1)H and (13)C nuclear magnetic resonance spectroscopy. ALA degradation was very efficiently inhibited by adjusting the pH of the aqueous solution to a value market introduction.

  18. Interfacial mechanisms for stability of surfactant-laden films

    CERN Document Server

    Bhamla, M Saad; Alvarez-Valenzuela, Marco A; Tajuelo, Javier; Fuller, Gerald G

    2016-01-01

    Thin liquid films are central to everyday life. They are ubiquitous in modern technology (pharmaceuticals, coatings), consumer products (foams, emulsions) and also serve vital biological functions (tear film of the eye, pulmonary surfactants in the lung). A common feature in all these examples is the presence of surface-active molecules at the air-liquid interface. Though they form only molecularly-thin layers, these surfactants produce complex surface stresses on the free surface, which have important consequences for the dynamics and stability of the underlying thin liquid film. Here we conduct simple thinning experiments to explore the fundamental mechanisms that allow the surfactant molecules to slow the gravity-driven drainage of the underlying film. We present a simple model that works for both soluble and insoluble surfactant systems. We show that surfactants with finite surface rheology influence bulk flow through viscoelastic interfacial stresses, while surfactants with inviscid surfaces achieve stab...

  19. Mechanical Stability Study for Integrable Optics Test Accelerator at Fermilab

    Energy Technology Data Exchange (ETDEWEB)

    McGee, Mike [Fermilab; Andrews, Richard [Fermilab; Carlson, Kermit [Fermilab; Leibfritz, Jerry [Fermilab; Nobrega, Lucy [Fermilab; Valishev, Alexander [Fermilab

    2016-07-01

    The Integrable Optics Test Accelerator (IOTA) is proposed for operation at Fermilab. The goal of IOTA is to create practical nonlinear accelerator focusing systems with a large frequency spread and stable particle motion. The IOTA is a 40 m circumference, 150 MeV (e-), 2.5 MeV (p⁺) diagnostic test ring. A heavy low frequency steel floor girder is proposed as the primary tier for IOTA device component support. Two design lengths; (8) 4 m and (2) 2.8 m long girders with identical cross section completely encompass the ring. This study focuses on the 4 m length girder and the development of a working prototype. Hydrostatic Level Sensor (HLS), temperature, metrology and fast motion measurements characterize the anticipated mechanical stability of the IOTA ring.

  20. Carbon stabilization mechanisms in soils in the Andes

    Science.gov (United States)

    Jansen, Boris; Cammeraat, Erik

    2015-04-01

    The volcanic ash soils of the Andes contain very large stocks of soil organic matter (SOM) per unit area. Consequently, they constitute significant potential sources or sinks of the greenhouse gas CO2. Climate and/or land use change potentially have a strong effect on these large SOM stocks. To clarify the role of chemical and physical stabilisation mechanisms in volcanic ash soils in the montane tropics, we investigated carbon stocks and stabilization mechanisms in the top- and subsoil along an altitudinal transect in the Ecuadorian Andes. The transect encompassed a sequence of paleosols under forest and grassland (páramo), including a site where vegetation cover changed in the last century. We applied selective extraction techniques, performed X-ray diffraction analyses of the clay fraction and estimated pore size distributions at various depths in the top- and subsoil along the transect. In addition, from several soils the molecular composition of SOM was further characterized with depth in the current soil as well as the entire first and the top of the second paleosol using GC/MS analyses of extractable lipids and Pyrolysis-GC/MS analyses of bulk organic matter. Our results show that organic carbon stocks in the mineral soil under forest a páramo vegetation were roughly twice as large as global averages for volcanic ash soils, regardless of whether the first 30cm, 100cm or 200cm were considered. We found the carbon stabilization mechanisms involved to be: i) direct stabilization of SOM in organo-metallic (Al-OM) complexes; ii) indirect protection of SOM through low soil pH and toxic levels of Al; and iii) physical protection of SOM due to a very high microporosity of the soil (Tonneijck et al., 2010; Jansen et al. 2011). When examining the organic carbon at a molecular level, interestingly we found extensive degradation of lignin in the topsoil while extractable lipids were preferentially preserved in the subsoil (Nierop and Jansen, 2009). Both vegetation

  1. Mechanical stability study for Integrable Optics Test Accelerator at Fermilab

    CERN Document Server

    McGee, M W; Carlson, K; Leibfritz, J; Nobrega, L; Valishev, A

    2016-01-01

    The Integrable Optics Test Accelerator (IOTA) is proposed for operation at Fermilab. The goal of IOTA is to create practical nonlinear accelerator focusing systems with a large frequency spread and stable particle motion. The IOTA is a 40 m circumference, 150 MeV (e-), 2.5 MeV (p+) diagnostic test ring. A heavy low frequency steel floor girder is proposed as the primary tier for IOTA device component support. Two design lengths; (8) 3.96 m and (2) 3.1 m long girders with identical cross section completely encompass the ring. This study focuses on the 3.96 m length girder and the development of a working prototype. Hydrostatic Level Sensor (HLS), temperature, metrology and fast motion measurements characterize the anticipated mechanical stability of the IOTA ring.

  2. Gelled Complex Fluids: Combining Unique Structures with Mechanical Stability.

    Science.gov (United States)

    Stubenrauch, Cosima; Gießelmann, Frank

    2016-03-01

    Gelled complex fluids are soft materials in which the microstructure of the complex fluid is combined with the mechanical stability of a gel. To obtain a gelled complex fluid one either adds a gelator to a complex fluid or replaces the solvent in a gel by a complex fluid. The most prominent example of a "natural" gelled complex fluid is the cell. There are various strategies by which one can form a gelled complex fluid; one such strategy is orthogonal self-assembly, that is, the independent but simultaneous formation of two coexisting self-assembled structures within one system. The aim of this Review is to describe the structure and potential applications of various man-made gelled complex fluids and to clarify whether or not the respective system is formed by orthogonal self-assembly.

  3. Measuring Mechanical Properties by Staring: Using Stress Assessment from Local Structural Anisotropy (SALSA) to Probe Viscosity and Visualize Stress Networks in Colloidal Suspensions

    Science.gov (United States)

    Cohen, Itai; Bierbaum, Matthew; Sethna, James; Lin, Neil

    2014-11-01

    Measurement of stress induced thermal fluctuations in materials can be used to determine macroscopic mechanical properties including viscosity in fluids, as well as bulk and shear moduli in solids. When extended to the single particle scale, such measurements also reveal underlying spatially inhomogeneous response mechanisms in systems such as glasses, gels, and polycrystals. Unfortunately, it is not possible to experimentally measure these temporal and spatial stress fluctuations in a colloidal suspension using conventional rheometers. Here however, we show that using fast confocal microscopy it is possible conduct a Stress Assessment from Local Structural Anisotropy (SALSA) to measure such spatio-temporal stress fluctuations. We directly image the microstructure of a nearly hard-sphere suspension using a high-speed confocal microscope and determine particle positions. We compute the structure anisotropy of the suspension and building on the Brady formalism, calculate particle-level stresses. In conjunction with the fluctuation-dissipation theorem, we then determine the bulk viscosity of a colloidal liquid. Furthermore, we show our local measurements allow direct visualization of the complex stress networks in a 3D supercooled liquid under compression. Our method provides an experimental approach that applies to a broad range of processes arising in sheared glasses, compressed gels, and even indented crystals.

  4. Mechanism study of stabilization of double-base propellants by using zeolite stabilizers (nano- and micro-clinoptilolite

    Directory of Open Access Journals (Sweden)

    M.A. Zayed

    2017-05-01

    Full Text Available The mechanism of stabilization of double-base rocket propellants (DBPs using inorganic stabilizer (nano- and micro-clinoptilolite was investigated. The surface structures of the stabilizers, the double-base propellants containing the new stabilizers and the effect of the stabilizers on the surface behavior of propellants and vice versa were checked using XRD and Electron Microscope (AFM and TEM techniques. The results obtained from XRD suggested that the crystalline structure of the new inorganic stabilizers was completely changed when it was introduced into the propellants which may be attributed to the pressing processes of DBPs with stabilizers under very high pressure during their mixture preparation. The results obtained from Atomic Force Electron Microscope (AFM and TEM indicated that nano-clinoptilolite particles become more regularly arranged on the propellant surface than micro-clinoptilolite which gives the stabilizer a higher ability to absorb more nitrogen oxide. The work aimed chiefly to use zeolite stabilizers for DBPs instead of classically used organic compounds; in order to avoid the harmful and carcinogenic organic products coming from the reaction of NOx gases with these organic stabilizers. This is achieved by studying the thermal behavior of these zeolites via investigation of their surface interaction with NOx gases obtained during stabilization process and suggesting possible interaction mechanism.

  5. Effect of surface charge on the colloidal stability and in vitro uptake of carboxymethyl dextran-coated iron oxide nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Ayala, Vanessa; Herrera, Adriana P.; Latorre-Esteves, Magda; Torres-Lugo, Madeline [University of Puerto Rico, Department of Chemical Engineering (United States); Rinaldi, Carlos, E-mail: carlos.rinaldi@bme.ufl.edu [University of Florida, J. Crayton Pruitt Family Department of Biomedical Engineering (United States)

    2013-08-15

    Nanoparticle physicochemical properties such as surface charge are considered to play an important role in cellular uptake and particle-cell interactions. In order to systematically evaluate the role of surface charge on the uptake of iron oxide nanoparticles, we prepared carboxymethyl-substituted dextrans with different degrees of substitution, ranging from 38 to 5 groups per chain, and reacted them using carbodiimide chemistry with amine-silane-coated iron oxide nanoparticles with narrow size distributions in the range of 33-45 nm. Surface charge of carboxymethyl-substituted dextran-coated nanoparticles ranged from -50 to 5 mV as determined by zeta potential measurements, and was dependent on the number of carboxymethyl groups incorporated in the dextran chains. Nanoparticles were incubated with CaCo-2 human colon cancer cells. Nanoparticle-cell interactions were observed by confocal laser scanning microscopy and uptake was quantified by elemental analysis using inductively coupled plasma mass spectroscopy. Mechanisms of internalization were inferred using pharmacological inhibitors for fluid-phase, clathrin-mediated, and caveola-mediated endocytosis. Results showed increased uptake for nanoparticles with greater negative charge. Internalization patterns suggest that uptake of the most negatively charged particles occurs via non-specific interactions.

  6. Colloidal Thermal Fluids

    Science.gov (United States)

    Lotzadeh, Saba

    In this dissertation, a reversible system with a well controlled degree of particle aggregation was developed. By surface modification of colloidal silica with aminosilanes, interactions among the particles were tuned in a controlled way to produce stable sized clusters at different pH values ranges from well-disposed to a colloidal gel. N-[3-(trimethoxysilyl)propyl]ethylenediamine (TMPE) monolayer on particle surface not only removes all the reactive sites to prevent chemical aggregation, also provides steric stabilization in the absence of any repulsion. After surface modification, electrokinetic behavior of silica particles were changed to that of amino groups, positive in acidic pH and neutral at basic pH values. By tuning the pH, the balance between electrostatic repulsion and hydrophobic interactions was reversibly controlled. As a result, clusters with different sizes were developed. The effect of clustering on the thermal conductivity of colloidal dispersions was quantified using silane-treated silica, a system engineered to exhibit reversible clustering under well-controlled conditions. Thermal conductivity of this system was measured by transient hot wire, the standard method of thermal conductivity measurements in liquids. We show that the thermal conductivity increases monotonically with cluster size and spans the entire range between the two limits of Maxwell's theory. The results, corroborated by numerical simulation, demonstrate that large increases of the thermal conductivity of colloidal dispersions are possible, yet fully within the predictions of classical theory. Numerical calculations were performed to evaluate the importance of structural properties of particles/aggregates on thermal conduction in colloidal particles. Thermal conductivity of non-spherical particles including hollow particles, cubic particles and rods was studied using a Monte Carlo algorithm. We show that anisotropic shapes, increase conductivity above that of isotropic

  7. Probing deviations from traditional colloid filtration theory by atomic forces microscopy.

    Energy Technology Data Exchange (ETDEWEB)

    Reno, Marissa Devan

    2005-12-01

    Colloid transport through saturated media is an integral component of predicting the fate and transport of groundwater contaminants. Developing sound predictive capabilities and establishing effective methodologies for remediation relies heavily on our ability to understand the pertinent physical and chemical mechanisms. Traditionally, colloid transport through saturated media has been described by classical colloid filtration theory (CFT), which predicts an exponential decrease in colloid concentration with travel distance. Furthermore, colloid stability as determined by Derjaguin-Landau-Veney-Overbeek (DLVO) theory predicts permanent attachment of unstable particles in a primary energy minimum. However, recent studies show significant deviations from these traditional theories. Deposition in the secondary energy minimum has been suggested as a mechanism by which observed deviations can occur. This work investigates the existence of the secondary energy minimum as predicted by DLVO theory using direct force measurements obtained by Atomic Forces Microscopy. Interaction energy as a function of separation distance between a colloid and a quartz surface in electrolyte solutions of varying ionic strength are obtained. Preliminary force measurements show promise and necessary modifications to the current experimental methodology have been identified. Stringent surface cleaning procedures and the use of high-purity water for all injectant solutions is necessary for the most accurate and precise measurements. Comparisons between direct physical measurements by Atomic Forces Microscopy with theoretical calculations and existing experimental findings will allow the evaluation of the existence or absence of a secondary energy minimum.

  8. Colloidal Covalent Organic Frameworks

    Science.gov (United States)

    2017-01-01

    Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material’s morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications. PMID:28149954

  9. Colloidal Covalent Organic Frameworks.

    Science.gov (United States)

    Smith, Brian J; Parent, Lucas R; Overholts, Anna C; Beaucage, Peter A; Bisbey, Ryan P; Chavez, Anton D; Hwang, Nicky; Park, Chiwoo; Evans, Austin M; Gianneschi, Nathan C; Dichtel, William R

    2017-01-25

    Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material's morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications.

  10. Thermal stability of nafion membranes under mechanical stress

    Energy Technology Data Exchange (ETDEWEB)

    Quintilii, M.; Struis, R. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-06-01

    The feasibility of adequately modified fluoro-ionomer membranes (NAFION{sup R}) is demonstrated for the selective separation of methanol synthesis products from the raw reactor gas at temperatures around 200{sup o}C. For an economically relevant application of this concept on a technical scale the Nafion membranes should be thin ({approx_equal}10 {mu}m) and thermally stable over a long period of time (1-2 years). In cooperation with industry (Methanol Casale SA, Lugano (CH)), we test the thermal stability of Nafion hollow fibers and supported Nafion thin sheet membranes at temperatures between 160 and 200{sup o}C under mechanical stress by applying a gas pressure difference over the membrane surface ({Delta}P{<=} 40 bar). Tests with the hollow fibers revealed that Nafion has visco-elastic properties. Tests with 50 {mu}m thin Nafion sheets supported by a porous metal carrier at 200{sup o}C and {Delta}P=39 bar showed no mechanical defects over a period of 92 days. (author) 5 figs., 4 refs.

  11. Rock mechanics stability at Olkiluoto, Haestholmen, Kivetty and Romuvaara

    Energy Technology Data Exchange (ETDEWEB)

    Johansson, E.; Rautakorpi, J. [Saanio and Riekkola Oy, Helsinki (Finland)

    2000-02-01

    Posiva Oy is studying the suitability of the Finnish bedrock for the geological disposal of spent nuclear fuel at four sites, Olkiluoto in Eurajoki, Haestholmen in Loviisa, Kivetty in Aeaenekoski and Romuvaara in Kuhmo. To enable the rock properties to be specified in great detail, the site-selection research programme has included rock mechanics investigations such as the measurement of in-situ rock stress and laboratory tests on rock samples. This report presents the results of the rock mechanics analyses performed on the main rock types at the Olkiluoto, Romuvaara, Kivetty and Haestholmen sites. The objective of this study was to assess the near-field stability of the final disposal tunnels and deposition holes at each of the investigation sites. Two empirical methods and a numerical method based on three-dimensional element code (3DEC) were used the analysis tools. A statistical approach was used to select the necessary input data and to specify the cases being analysed. The stability of the KBS-3 and MLH (Medium Long Hole) repository concepts during the pre-closure and post-closure phases was analysed. The repository depths investigated lay between 300 m and 700 m. The empirical methods are based on the study of the ratios between rock strength and the in-situ stress which could result in possible fracturing of the rock mass. Interpretation of the numerical analyses is based on the assumption of an elastic distribution of stress around the disposal tunnel and the deposition hole and the brittle rock strength criterion. The results obtained in this study indicate that in general, the rock mechanics conditions during the pre-closure and post-closure phases at each of the investigated sites remain good and stable between the studied depth levels, especially when the deposition rooms are oriented in a direction parallel to the major in-situ stress. If the disposal tunnels are orientated in a direction perpendicular to the major in-situ stress, the resultant

  12. Colloidal Double Quantum Dots.

    Science.gov (United States)

    Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon

  13. Surface speciation of myo-inositol hexakisphosphate adsorbed on TiO{sub 2} nanoparticles and its impact on their colloidal stability in aqueous suspension: A comparative study with orthophosphate

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Biao; Yan, Yupeng; Liu, Fan; Tan, Wenfeng; He, Jiajie; Feng, Xionghan, E-mail: fxh73@mail.hzau.edu.cn

    2016-02-15

    Despite extensive research demonstrating the influence of organic matter and inorganic phosphate on the stability of TiO{sub 2} nanoparticles (NPs), far less research has assessed the impact of myo-inositol hexakisphosphate (IHP), a common organic phosphate widely present in the environment. In this study, the adsorption of IHP on TiO{sub 2} NPs and its impact on their colloidal stability were investigated using batch experiments, dynamic light scattering (DLS) techniques, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) and solid-state {sup 31}P nuclear magnetic resonance (NMR) spectroscopy. Inorganic orthophosphate (P{sub i}) adsorption was run for comparison. The ratio of the P{sub i}/IHP adsorption density (1.528: 0.453) at pH 5.0 suggested that IHP may complex on the TiO{sub 2} surface through three of its six phosphate groups. Zeta potential measurements, ATR-FTIR and NMR spectra indicated that IHP/P{sub i} adsorbed onto TiO{sub 2} NPs by forming inner-sphere complexes and modified the surface charge of these NPs, which exerted a great impact on their colloidal stability. Interactions between NPs measured by sedimentation and aggregation size highly depended on the pH, surface phosphorus coverage, and surface phosphorus species. The impact of IHP on the aggregation and dispersion of TiO{sub 2} NPs was significantly larger than that of P{sub i}, in agreement with the calculation from the DLVO theory. This study highlighted the impact of IHP relative to P{sub i} on the colloidal stability of TiO{sub 2} NPs in phosphorus-enriched environments. - Highlights: • IHP/P{sub i} plays a significant role in the colloidal stability of TiO{sub 2} NPs. • The effect of IHP is much greater than P{sub i}. • TiO{sub 2} surface charge is modified by the formed inner-sphere P complexes. • IHP binds on TiO{sub 2} by 3 of its 6 P groups leaving the other 3 dissociated and ionized. • Interaction between NPs depends on pH, surface P coverage, and

  14. Composition, stabilisation and cleavage of crude oil emulsions. Pt. 1. Mechanism of stabilization and cleavage of crude oil emulsions. Aufbau, Stabilisierung und Spaltung von Rohoelemulsionen. T. 1. Mechanismus der Stabilisierung und Spaltung von Rohoelemulsionen

    Energy Technology Data Exchange (ETDEWEB)

    Oetter, G. (BASF AG, Ludwigshafen am Rhein (Germany). Forschungsabteilung); Oppenlaender, K. (BASF AG, Ludwigshafen am Rhein (Germany). Forschungsabteilung)

    Asphaltenes and resins, two chemically and structurally different colloid fractions, are responsible for the stability of crude oil emulsions. Their aggregation behavior and interfacial properties are studied. The crude oil stability is mainly governed by the shear viscosity and elasticity of the interfacial film and less by the interfacial tension. The mechanism of emulsion destabilization by chemical demulsifiers as well as coagulation and coalescence of the water droplets are discussed. The effectiveness of the demulsifier can be monitored by physicochemical parameters of the interfacial film. (orig.)

  15. Mechanical properties of yttria-stabilized zirconia ceramics

    Science.gov (United States)

    Shirooyeh A, Mahmood R.

    Superplasticity is a well-known characteristic of Y2O 3-stabilized tetragonal zirconia (3Y-TZP) ceramic composites at elevated temperatures. The present investigation was originated to evaluate the potential of producing zirconia ceramics suitable for achieving superplasticity. High purity 3 mol% Y2O3-stabilized tetragonal zirconia (3Y-TZP) ceramic composites containing 20 wt% alumina were successfully consolidated by application of Cold Isostatic Pressing (CIP) followed by a subsequent sintering process. Constant-stress tensile creep experiments at elevated temperatures were conducted in order to examine plastic deformation behavior of the material. In addition to mechanical testing data, the microstructure observations confirmed superplastic properties of the ceramic composite. It is also known that in order to attain High Strain Rate Superplasticity (HSRS) in zirconia ceramics, it is essential to retain a stable fine-grained microstructure at high temperatures. Experiments have confirmed that adding a second soft phase such as spinel can facilitate to reach high strain-rate superplasticity in zirconia ceramics by suppressing grain growth during sintering process and enhancing cation diffusion. In the present investigation, homogenous 3Y-TZP ceramic composite powders containing 30 vol% MgAl2O4 spinel were successfully prepared through both physical-based and chemical-based methods. An electric current-activated method known as Spark Plasma Sintering (SPS) was employed for powder consolidation process. This is a very rapid electric current-activated sintering technique having a heating rate of 300 K/min. The powder preparation and consolidation steps were carried out over a wide range of conditions to ensure a homogenous nanocomposite. The experiments showed that fully-dense zirconia ceramics with an average initial grain size of the order of ˜100 nm can be sintered at the relatively low processing temperature of 1373 K in 10 min. In order to study the

  16. Colloid Release from Soil Aggregates

    DEFF Research Database (Denmark)

    Vendelboe, Anders Lindblad; Møldrup, Per; Schjønning, Per;

    2012-01-01

    The content of water-dispersible colloids (WDC) has a major impact on soil functions and structural stability. In addition, the presence of mobile colloids may increase the risk of colloid-facilitated transport of strongly sorbing environmental contaminants. The WDC content was measured in 39 soils......, using laser diffraction, by agitating the samples using a wet-dispersion unit. This approach eliminated the need for long sedimentation times required by the more classical end-over-end shaking approach and provided information about the time-dependent release of WDC. The total clay content of the soils...... ranged from 0.1 to 0.44 kg kg−1. The WDC content was measured on air-dry and moist 1- to 2-mm aggregates. The WDC content at a reference time was highly correlated to the total clay content (r > 0.91, P soils. Only for two sites was the WDC content correlated to the content of clay...

  17. Towards Directional Colloidal Interactions

    NARCIS (Netherlands)

    Kamp, M.

    2015-01-01

    Colloids are particles with a size on the scale of microns in at least one dimension. The central theme of this thesis is the synthesis of model colloids with anisotropic interactions - often called `patchy' colloids, as well as the search for new ways to assemble such colloids. Methods to build

  18. Stability conditions and mechanism of cream soaps: role of glycerol.

    Science.gov (United States)

    Sagitani, Hiromichi

    2014-01-01

    Fatty acids, fatty acid potassium soaps, glycerol and water are essential ingredients in the production of stable cream soaps. In this study, the behavior of these components in solution was investigated to elucidate the stability conditions and mechanism of cream soaps. It was determined that the cream soaps were a dispersion of 1:1 acid soap (1:1 molar ratio of potassium soap/fatty acid) crystals in the lamellar gel phase, which has confirmed from the phase behavior diagrams and small angle X-ray scattering data. Glycerol was crucial ingredient in the formation of the lamellar gel phase. The cleansing process of the cream soaps was also evaluated using the same diagrams. The structure of the continuous phase in cream soaps changed from lamellar gel to a micellar aqueous solution upon the addition of water. This structural change during the washing process is important in producing the foaming activity of acid soaps to wash away dirt or excess fats from the skin surface.

  19. An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals

    Directory of Open Access Journals (Sweden)

    Parul Chawla

    2014-08-01

    Full Text Available In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO and tri-n-octylphosphine (TOP and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern–Volmer quenching constant (KSV and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor–acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe. Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications.

  20. An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals.

    Science.gov (United States)

    Chawla, Parul; Singh, Son; Sharma, Shailesh Narain

    2014-01-01

    In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern-Volmer quenching constant (K SV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor-acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications.

  1. Exercise of mechanisms of dynamic stability improves the stability state after an unexpected gait perturbation in elderly.

    Science.gov (United States)

    Bierbaum, Stefanie; Peper, Andreas; Arampatzis, Adamantios

    2013-10-01

    Unexpected changes during gait challenge elderly individuals to a greater degree than young adults. However, the adaptive potential of elderly seems to be retained, and therefore, the training of the mechanisms of dynamic stability as well as muscle strength training may improve the dynamic stability after unexpected perturbations. Thirty-eight subjects (65-75 years) participated in the study, divided into two experimental groups (stability training group, ST, n = 14 and mixed training group, MT, n = 14) and a control group (CG, n = 10). Both experimental groups performed exercises which focused on the mechanisms of dynamic stability. Additionally, the MT group executed a training to improve muscle strength. Session volume and duration were equal for both groups (14 weeks, twice a week, ~1.5 h per session). Pre- and post-intervention, subjects performed a gait protocol with an induced unexpected perturbation. Post-intervention, the margin of stability was significantly increased after the unexpected perturbation in the ST group, indicating an improvement in stability state (pre, -30.3 ± 5.9 cm; post, -24.1 ± 5.2 cm). Further, both intervention groups increased their base of support after the intervention to regain balance after gait perturbation, whereas only the ST group showed a statistically significant improvement (STpre, 90.9 ± 6.6 cm, STpost, 98.2 ± 8.5 cm; MTpre, 91.4 ± 6.2 cm; MTpost, 97.9 ± 12.7 cm). The CG showed no differences between pre- and post-measurements. The exercise of the mechanisms of dynamic stability led to a better application of these mechanisms after an unexpected perturbation during gait. We suggest that the repeated exercise of the mechanisms of dynamic stability contributes to significant improvements in postural stability. Additional strength training for healthy elderly individuals, however, shows no further effect on the ability to recover balance after unexpected perturbations during gait.

  2. Flocking ferromagnetic colloids

    Science.gov (United States)

    Kaiser, Andreas; Snezhko, Alexey; Aranson, Igor S.

    2017-01-01

    Assemblages of microscopic colloidal particles exhibit fascinating collective motion when energized by electric or magnetic fields. The behaviors range from coherent vortical motion to phase separation and dynamic self-assembly. Although colloidal systems are relatively simple, understanding their collective response, especially under out-of-equilibrium conditions, remains elusive. We report on the emergence of flocking and global rotation in the system of rolling ferromagnetic microparticles energized by a vertical alternating magnetic field. By combing experiments and discrete particle simulations, we have identified primary physical mechanisms, leading to the emergence of large-scale collective motion: spontaneous symmetry breaking of the clockwise/counterclockwise particle rotation, collisional alignment of particle velocities, and random particle reorientations due to shape imperfections. We have also shown that hydrodynamic interactions between the particles do not have a qualitative effect on the collective dynamics. Our findings shed light on the onset of spatial and temporal coherence in a large class of active systems, both synthetic (colloids, swarms of robots, and biopolymers) and living (suspensions of bacteria, cell colonies, and bird flocks). PMID:28246633

  3. Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet

    Energy Technology Data Exchange (ETDEWEB)

    Frisch, Josef; Chang, Allison; Decker, Valentin; Doyle, Eric; Eriksson, Leif; Hendrickson, Linda; Himel, Thomas; Markiewicz, Thomas; Partridge, Richard; Seryi, Andrei; /SLAC

    2006-09-28

    The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system.

  4. Thermo-Mechanical Methodology for Stabilizing Shape Memory Alloy Response

    Science.gov (United States)

    Padula, Santo

    2013-01-01

    This innovation is capable of significantly reducing the amount of time required to stabilize the strain-temperature response of a shape memory alloy (SMA). Unlike traditional stabilization processes that take days to weeks to achieve stabilized response, this innovation accomplishes stabilization in a matter of minutes, thus making it highly useful for the successful and practical implementation of SMA-based technologies in real-world applications. The innovation can also be applied to complex geometry components, not just simple geometries like wires or rods.

  5. Photo-stability and time-resolved photoluminescence study of colloidal CdSe/ZnS quantum dots passivated in Al{sub 2}O{sub 3} using atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Chih-Yi [Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan (China); Mao, Ming-Hua, E-mail: mhmao@ntu.edu.tw [Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan (China); Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

    2016-08-28

    We report photo-stability enhancement of colloidal CdSe/ZnS quantum dots (QDs) passivated in Al{sub 2}O{sub 3} thin film using the atomic layer deposition (ALD) technique. 62% of the original peak photoluminescence (PL) intensity remained after ALD. The photo-oxidation and photo-induced fluorescence enhancement effects of both the unpassivated and passivated QDs were studied under various conditions, including different excitation sources, power densities, and environment. The unpassivated QDs showed rapid PL degradation under high excitation due to strong photo-oxidation in air while the PL intensity of Al{sub 2}O{sub 3} passivated QDs was found to remain stable. Furthermore, recombination dynamics of the unpassivated and passivated QDs were investigated by time-resolved measurements. The average lifetime of the unpassivated QDs decreases with laser irradiation time due to photo-oxidation. Photo-oxidation creates surface defects which reduces the QD emission intensity and enhances the non-radiative recombination rate. From the comparison of PL decay profiles of the unpassivated and passivated QDs, photo-oxidation-induced surface defects unexpectedly also reduce the radiative recombination rate. The ALD passivation of Al{sub 2}O{sub 3} protects QDs from photo-oxidation and therefore avoids the reduction of radiative recombination rate. Our experimental results demonstrated that passivation of colloidal QDs by ALD is a promising method to well encapsulate QDs to prevent gas permeation and to enhance photo-stability, including the PL intensity and carrier lifetime in air. This is essential for the applications of colloidal QDs in light-emitting devices.

  6. Manipulating colloids with charges and electric fields

    Science.gov (United States)

    Leunissen, M. E.

    2007-02-01

    This thesis presents the results of experimental investigations on a variety of colloidal suspensions. Colloidal particles are at least a hundred times larger than atoms or molecules, but suspended in a liquid they display the same phase behavior, including fluid and crystalline phases. Due to their relatively large size, colloids are much easier to investigate and manipulate, though. This makes them excellent condensed matter model systems. With this in mind, we studied micrometer-sized perspex (‘PMMA’) spheres, labeled with a fluorescent dye for high-resolution confocal microscopy imaging, and suspended in a low-polar mixture of the organic solvents cyclohexyl bromide and cis-decalin. This system offered us the flexibility to change the interactions between the particles from ‘hard-sphere-like’ to long-ranged repulsive (between like-charged particles), long-ranged attractive (between oppositely charged particles) and dipolar (in an electric field). We investigated the phase behavior of our suspensions as a function of the particle concentration, the ionic strength of the solvent and the particles’ charges. In this way, we obtained new insight in the freezing and melting behavior of like-charged and oppositely charged colloids. Interestingly, we found that the latter can readily form large crystals, thus defying the common belief that plus-minus interactions inevitably lead to aggregation. Moreover, we demonstrated that these systems can serve as a reliable model system for classical ionic matter (‘salts’), and that opposite-charge interactions can greatly facilitate the self-assembly of new structures with special properties for applications. On a slightly different note, we also studied electrostatic effects in mixtures of the cyclohexyl bromide solvent and water, both with and without colloidal particles present. This provided new insight in the stabilization mechanisms of oil-water emulsions and gave us control over the self-assembly of various

  7. Highly Elastic and Self-Healing Composite Colloidal Gels.

    Science.gov (United States)

    Diba, Mani; Wang, Huanan; Kodger, Thomas E; Parsa, Shima; Leeuwenburgh, Sander C G

    2017-03-01

    Composite colloidal gels are formed by the pH-induced electrostatic assembly of silica and gelatin nanoparticles. These injectable and moldable colloidal gels are able to withstand substantial compressive and tensile loads, and exhibit a remarkable self-healing efficiency. This study provides new, critical insight into the structural and mechanical properties of composite colloidal gels and opens up new avenues for practical application of colloidal gels.

  8. The colloid investigations conducted at the Aespoe Hard Rock Laboratory during 2000-2004

    Energy Technology Data Exchange (ETDEWEB)

    Laaksoharju, Marcus [Geopoint AB, Stockholm (Sweden); Wold, Susanna [Royal Inst. of Tech., Stockholm (Sweden). School of Chemical Science and Engineering, Nuclear Chemistry] (eds.)

    2005-12-15

    In 2000, SKB decided to initiate an international colloid project at the Aespoe Hard Rock Laboratory in Sweden. The objectives of the colloid project are to: (i) study the role of bentonite as a colloid source, (ii) verify the background colloid concentration at Aespoe HRL and, (iii) investigate the potential for colloid formation/transport in natural groundwater concentrations. The experimental concepts for the colloid project are: laboratory experiments with bentonite, background field measurements of natural colloids, borehole specific bentonite colloid stability experiments and a fracture specific transport experiment. The activities concerning the laboratory experiments and background field measurements are described in this work; the other activities are ongoing or planned. The following conclusions were made: The bentonite colloid stability is strongly dependent on the groundwater ionic strength. Natural colloids are organic degradation products such as humic and fulvic acids, inorganic colloids (clay, calcite, iron hydroxide) and microbes. Microbes form few but large particles and their concentration increase with increasing organic carbon concentrations. The small organic colloids are present in very low concentrations in deep granitic groundwater. The concentrations can be rather high in shallow waters. The colloid concentration decreases with depth and salinity, since colloids are less stable in saline waters. The colloid content at Aespoe is less than 300 ppb. The colloid content at repository level is less than 50 ppb. The groundwater variability obtained in the boreholes reflects well the natural groundwater variability along the whole HRL tunnel.

  9. A theoretical study of mechanical stability of arteries.

    Science.gov (United States)

    Rachev, Alexander

    2009-05-01

    This study proposes a mathematical model for studying stability of arteries subjected to a longitudinal extension and a periodic pressure. An artery was considered as a straight composite beam comprised of an external thick-walled tube and a fluid core. The dynamic criterion for stability was used, based on analyzing the small transverse vibrations superposed on the finite deformation of the vessel under static load. In contrast to the case of a static pressurization, in which buckling is only possible if the load produces a critical axial compressive force, a loss of stability of arteries under periodic pressure occurs under many combinations of load parameters. Instability occurs as a parametric resonance characterized by an exponential increase in the amplitude of transverse vibrations over several bands of pressure frequencies. The effects of load parameters were analyzed on the basis of the results for a dynamic and static stability of a rabbit thoracic aorta. Under normal physiological loads the artery is in a stable configuration. Static instability occurs under high distending pressures and low longitudinal stretch ratios. When the artery is subjected to periodic pressure, an independent increase in the mean pressure, amplitude of the periodic pressure, or frequency, most often, but not always, increases the risk of stability loss. In contrary, an increase in longitudinal stretch ratio most likely, but not certain, stabilizes the vessel. It was shown that adaptive geometrical remodeling due to an increase in mean pressure and flow does not affect artery stability.

  10. Interactions in Natural Colloid Systems "Biosolids" - Soil and Plant

    Science.gov (United States)

    Kalinichenko, Kira V.; Nikovskaya, Galina N.; Ulberg, Zoya R.

    2016-04-01

    The "biosolids" are complex biocolloid system arising in huge amounts (mln tons per year) from biological municipal wastewater treatment. These contain clusters of nanoparticles of heavy metal compounds (in slightly soluble or unsoluble forms, such as phosphates, sulphates, carbonates, hydroxides, and etc.), cells, humic substances and so on, involved in exopolysaccharides (EPS) net matrix. One may consider that biosolids are the natural nanocomposite. Due to the presence of nitrogen, phosphorus, potassium and other macro- and microelements (heavy metals), vitamins, aminoacids, etc., the biosolids are a depot of bioelements for plant nutrition. Thus, it is generally recognized that most rationally to utilize them for land application. For this purpose the biocolloid process was developed in biosolids system by initiation of microbial vital ability followed by the synthesis of EPS, propagation of ecologically important microorganisms, loosening of the structure and weakening of the coagulation contacts between biosolids colloids, but the structure integrity maintaining [1,2]. It was demonstrated that the applying of biosolids with metabolizing microorganisms to soil provided the improving soil structure, namely the increasing of waterstable aggregates content (70% vs. 20%). It occurs due to flocculation ability of biosolids EPS. The experimental modelling of mutual interactions in systems of soils - biosolids (with metabolizing microorganisms) were realized and their colloid and chemical mechanisms were formulated [3]. As it is known, the most harmonious plant growth comes at a prolonged entering of nutrients under the action of plant roots exudates which include pool of organic acids and polysaccharides [4]. Special investigations showed that under the influence of exudates excreted by growing plants, the biosolids microelements can release gradually from immobilized state into environment and are able to absorb by plants. Thus, the biosolids can serve as an active

  11. Aggregation kinetics of inorganic colloids in eutrophic shallow lakes: Influence of cyanobacterial extracellular polymeric substances and electrolyte cations.

    Science.gov (United States)

    Xu, Huacheng; Yang, Changming; Jiang, Helong

    2016-12-01

    The stability/aggregation propensity of inorganic colloids in eutrophic shallow lakes is of great essence in governing the water transparency and contaminant behavior. In this study, time-resolved dynamic light scattering was employed to investigate the aggregation kinetics of Al2O3 inorganic colloids over a wide range of cyanobacterial extracellular polymeric substance (EPS) concentrations in the absence and presence of electrolyte cations. The results showed that EPS adsorption alone greatly decreased the hydrodynamic diameters of colloidal particles, whose stability behavior followed closely the predictions of the classical DLVO theory. Electrolyte cations, however, can induce the aggregation of colloidal particles, and divalent Ca(2+) were found to be more efficient in destabilizing the colloids than monovalent Na(+), as indicated by the considerably lower critical coagulation concentrations (2.5 mM for Ca(2+) vs. 170 mM for Na(+)). Further addition of Ca(2+), i.e., >2.5 mM, caused an extremely high aggregation degree and rate. High resolution transmission electron microscopy revealed that this enhanced aggregation should be attributed to the gel-like bridging between colloidal particles, which were verified to be the amorphous EPS-Ca(2+) complexes. Field-emission scanning electron microscopy coupled with elemental mapping provided additional evidence that the bridging interaction of EPS with Ca(2+) was the predominant mechanism for the aggregation enhancement. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Microscopic mechanism of stability in yttria-doped zirconia

    CERN Document Server

    Ostanin, S A

    2001-01-01

    The relaxed configurations of yttria-stabilized zirconia (YSZ) between 3 and 10 mol. % Y sub 2 O sub 3 were modeled within the pseudopotential technique. The vibration mode corresponding to the soft phonon in pure c-ZrO sub 2 has been calculated for each Y sub 2 O sub 3 composition. These anharmonic vibrations, associated with stabilization of YSZ, have been investigated within the self-consistent phonon approximation that makes obtainable the fine structure in spectral density. In studying the phonon dynamics, it is proposed to use the displacement probability density which can quantify very accurately the transition temperature needed to stabilize the YSZ cubic phase

  13. Adsorption mechanism of physiologically active L-phenylalanine phosphonodipeptide analogues: Comparison of colloidal silver and macroscopic silver substrates

    Science.gov (United States)

    Podstawka, E.; Kudelski, A.; Proniewicz, L. M.

    2007-11-01

    Here we present SERS spectra of several L-phenylalanine (Phe) phosphonodipeptides, i.e., L-Phe- L-Ala-PO 3H 2 ( MD1), L-Phe- L-Va L-PO 3H 2 ( MD2), L-Phe-β-Ala-CH(OH)-PO 3H 2 ( MD3), L-Phe- L-Ala-CH(OH)-PO 3H 2 ( MD4), L-Ala-(3,4-dimethoxy)- L-Phe-PO 3H 2 ( MD5), and L-Ala-(3,4-dimethoxy)-(des-CH 2)- L-Phe-PO 3H 2 ( MD6), immobilized on electrochemically roughened silver electrodes. These spectra are analyzed by theoretical calculations using density functional theory (DFT) at the B3LYP level with 6-31++G∗∗ basis set. In addition, these spectra are compared with SERS spectra of these species adsorbed on a colloidal silver surface. We showed that on the macroscopic silver substrate, the Phe aromatic ring of MD3 and MD4 is oriented vertically, while for MD1 it almost "stands up" on this surface. In the other three cases, the Phe ring adopts a tilted orientation in regard to the substrate. We also find that the phosphonate (-PO32-), methyl/methane, or dimethoxy groups of MD1, MD2, MD3, MD5, and MD6 are involved in the interaction of these phosphonodipeptides with the electrochemically roughened surface. This phenomenon is clearly seen for -CH 2-/-CH 3/-OCH 3 moieties as well as for the PO32- group that adsorbs on the macroscopic silver substrates mainly via the P dbnd O fragment. We also showed that MD4 binds to the macroscopic silver substrate through the hydroxyl, amine, and phosphonate groups, while the methylene/methane moieties are remote from this surface. We found that studied phosphonodipeptides often adsorb differently on the macroscopic silver substrate and on the colloidal silver nanoparticles. For example, MD1 adopts an almost vertical orientation on the electrochemically roughened silver substrate and is tilted or close to flat on the silver nanoparticles.

  14. Mechanism study on stability enhancement of adefovir dipivoxil by cocrystallization: Degradation kinetics and structure-stability correlation.

    Science.gov (United States)

    Lin, Rui-Zhen; Sun, Peng-Jie; Tao, Qian; Yao, Jia; Chen, Jia-Mei; Lu, Tong-Bu

    2016-03-31

    The purpose of this study is to determine the mechanism by which cocrystallization can enhance the stability of adefovir dipivoxil (AD), a diester prodrug of adefovir with known chemical stability problem. Three multi-component crystals of AD with biologically safe coformers, including gallic acid cocrystal hydrate (1:1:1), salicylate salt (1:1), and maleate salt (1:1) were prepared and characterized by thermal analysis, infrared spectroscopy, powder and single crystal X-ray diffraction. DVS measurements and stability tests were applied to evaluate the stability. The new crystalline phases exhibit improved stability compared to pure drug in the order AD gallic acid cocrystal>AD maleate>AD salicylate>AD form I. Degradation kinetics and structure-stability correlation studies demonstrate that the stability enhancement mechanism by cocrystallization involves (1) inhibition of hydrolysis of AD by replacement of drug-drug homosynthons by stronger drug-coformer heterosynthons at adenine fragments; (2) suppression of dimerization of AD by separation of adenine fragments by inserting coformers in crystal lattices; (3) further reducing rates of hydrolysis by forming hydrogen bonds with hydrate water at phosphoryl fragments. This study has important implications for use of cocrystallization approach to some easily degradable drugs in pharmaceutical.

  15. Formation of uranium(IV)-silica colloids at near-neutral pH

    Science.gov (United States)

    Dreissig, Isabell; Weiss, Stephan; Hennig, Christoph; Bernhard, Gert; Zänker, Harald

    2011-01-01

    Evidence is provided by photon correlation spectroscopy, ultrafiltration and ultracentrifugation that uranium(IV) can form silicate-containing colloids of a size of ⩽20 nm. A concentration of up to 10 -3 M of colloid-borne U(IV) was observed. The particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. Electrostatic repulsion due to a negative zeta potential in the near-neutral to alkaline pH range caused by the silicate stabilizes the U(IV) colloids. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate. The mechanism of the colloidal stabilization can be regarded as "sequestration" by silicate, a phenomenon well known from heavy metal ions of high ion potential such as iron(III) or manganese(III,IV), but never reported for uranium(IV) so far. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids. The next-neighbor coordination of U(IV) in the U(IV)-silica colloids is comparable with that of coffinite, USiO 4. The assessment of uranium behavior in the aquatic environment should take the possible existence of U(IV)-silica colloids into consideration. Their occurrence might influence uranium migration in anoxic waters.

  16. Mechanism of Stabilization of Labile Compounds by Silk Fibroin Proteins

    Science.gov (United States)

    2017-04-05

    stabilization and recovery. This approach can provide expanded utility for remote collection of blood and other biospecimens empowering new modalities of...a few different analyte-specific reconstitution buffers will be well tolerated in industry, assuming there is at least some broader cross -analyte...glycerol and sucrose, protein stability corresponded well to expectations based on neutron scattering data. Furthermore, two screening techniques were

  17. Reinforcement mechanism of slope stability method with no cutting trees

    OpenAIRE

    Yuki, Chikata; Harushige, KUSUMI; 楠見, 晴重; Katsumi, TERAOKA

    2008-01-01

    The study in this paper is the slope stability. Although many slopes are prone to collapse, countermeasures against slop failures have not been progressed yet in Japan. Most slope protection methods were to cover shotcrete on the slope in 1960’s. However, the slope covered shotcrete have been deteriorating. Therefore, the slope failures frequently occur due to the natural disaster such as heavy rainfall and earthquake. It is important to develop an effective slope stability method. Moreover, ...

  18. Protein's native state stability in a chemically induced denaturation mechanism.

    Science.gov (United States)

    Olivares-Quiroz, L; Garcia-Colin, L S

    2007-05-21

    In this work, we present a generalization of Zwanzig's protein unfolding analysis [Zwanzig, R., 1997. Two-state models of protein folding kinetics. Proc. Natl Acad. Sci. USA 94, 148-150; Zwanzig, R., 1995. Simple model of protein folding kinetics. Proc. Natl Acad. Sci. USA 92, 9801], in order to calculate the free energy change Delta(N)(D)F between the protein's native state N and its unfolded state D in a chemically induced denaturation. This Extended Zwanzig Model (EZM) is both based on an equilibrium statistical mechanics approach and the inclusion of experimental denaturation curves. It enables us to construct a suitable partition function Z and to derive an analytical formula for Delta(N)(D)F in terms of the number K of residues of the macromolecule, the average number nu of accessible states for each single amino acid and the concentration C(1/2) where the midpoint of the ND transition occurs. The results of the EZM for proteins where chemical denaturation follows a sigmoidal-type profile, as it occurs for the case of the T70N human variant of lysozyme (PDB code: T70N) [Esposito, G., et al., 2003. J. Biol. Chem. 278, 25910-25918], can be splitted into two lines. First, EZM shows that for sigmoidal denaturation profiles, the internal degrees of freedom of the chain play an outstanding role in the stability of the native state. On the other hand, that under certain conditions DeltaF can be written as a quadratic polynomial on concentration C(1/2), i.e., DeltaF approximately aC(1/2)(2)+bC(1/2)+c, where a,b,c are constant coefficients directly linked to protein's size K and the averaged number of non-native conformations nu. Such functional form for DeltaF has been widely known to fit experimental measures in chemically induced protein denaturation [Yagi, M., et al., 2003. J. Biol. Chem. 278, 47009-47015; Asgeirsson, B., Guojonsdottir, K., 2006. Biochim. Biophys. Acta 1764, 190-198; Sharma, S., et al., 2006. Protein Pept. Lett. 13(4), 323-329; Salem, M., et al

  19. Optical-Mechanical System for Stabilizing an Inverted Pendulum

    Science.gov (United States)

    Kuzyakov, O. N.; Andreeva, M. A.

    2016-08-01

    Controlling open-loop unstable systems is a common benchmark for designing the algorithms to maintain the equilibrium state of anthropomorphous technical devices used within control theory. In this connection, considerable attention is currently being focused on the problem of stabilizing the inverted pendulum system. In this work, the execution of swinging-up the pendulum and, subsequently, maintaining its upward equilibrium state is presented with the help of the laboratory bench TP-802 by Festo Didactics and the movement control device. The configuration of dynamic system for stabilizing the inverted pendulum is offered. The algorithms to swing-up the pendulum and balance it around its upright position are offered as well.

  20. Indefinite damping in mechanical systems and gyroscopic stabilization

    DEFF Research Database (Denmark)

    Kliem, Wolfhard; Pommer, Christian

    2009-01-01

    This paper deals with gyroscopic stabilization of the unstable system Mx + D(x) over dot + K-x = 0, with positive definite mass and stiffness matrices M and K, respectively, and an indefinite damping matrix D. The main question if for which skew-symmetric matrices G the system Mx (D+ G)(x) over d...... + K-x = 0 can become stable? After investigating special cases we find an appropriat solution of the Lyapunov matrix equation for the general case. Examples show the deviation of the stability limit found by the Lyapunov method from the exact value....

  1. Colloid Transport and Retention

    DEFF Research Database (Denmark)

    Yuan, Hao; Shapiro, Alexander

    2012-01-01

    Book Description: Colloidal science and technology is one of the fastest growing research and technology areas. This book explores the cutting edge research in colloidal science and technology that will be usefull in almost every aspect of modern society. This book has a depth of information...... related to historical prospective, synthesis, characterization, theoretical modeling and application of unique class of colloidal materials starting from colloidal gold to coated silica colloid and platinum, titania colloids. This book is unique in its design, content, providing depth of science about...... different colloidal materials and their applications in chemistry, physics, biological, medical sciences and environment. Graduate students, academic and industrial researchers and medical professionals will discover recently developed colloidal materials and their applications in many areas of human...

  2. Pathogen removal mechanisms in macrophyte and algal waste stabilization ponds

    NARCIS (Netherlands)

    Awuah, E.

    2006-01-01

    Waste stabilization ponds are recognized as the solution to domestic wastewater treatment in developing countries. This is because it is cheap, easy to construct and do not require high skilled labour. In the developing countries the objectives for wastewater treatment should put emphasis on pathoge

  3. Pathogen removal mechanisms in macrophyte and algal waste stabilization ponds

    NARCIS (Netherlands)

    Awuah, E.

    2006-01-01

    Waste stabilization ponds are recognized as the solution to domestic wastewater treatment in developing countries. The use of such natural systems is considered to be very important. This is because it is cheap, easy to construct and they do not require high skilled labour. In the developing countri

  4. Identifying failure mechanisms in LDMOS transistors by analytical stability analysis

    NARCIS (Netherlands)

    Ferrara, A.; Steeneken, P.G.; Boksteen, B.K.; Heringa, A.; Scholten, A.J.; Schmitz, J.; Hueting, R.J.E.

    2014-01-01

    In this work, analytical stability equations are derived and combined with a physics-based model of an LDMOS transistor in order to identify the primary cause of failure in different operating and bias conditions. It is found that there is a gradual boundary between an electrical failure region at h

  5. Pathogen removal mechanisms in macrophyte and algal waste stabilization ponds

    NARCIS (Netherlands)

    Awuah, E.

    2006-01-01

    Waste stabilization ponds are recognized as the solution to domestic wastewater treatment in developing countries. The use of such natural systems is considered to be very important. This is because it is cheap, easy to construct and they do not require high skilled labour. In the developing countri

  6. Structural transitions in condensed colloidal virus phases

    Science.gov (United States)

    Schmidt, Nathan; Barr, Steve; Udit, Andrew; Gutierrez, Leonardo; Nguyen, Thanh; Finn, M. G.; Luijten, Erik; Wong, Gerard

    2010-03-01

    Analogous to monatomic systems colloidal phase behavior is entirely determined by the interaction potential between particles. This potential can be tuned using solutes such as multivalent salts and polymers with varying affinity for the colloids to create a hierarchy of attractions. Bacteriophage viruses are a naturally occurring type of colloidal particle with characteristics difficult to achieve by laboratory synthesis. They are monodisperse, nanometers in size, and have heterogeneous surface charge distributions. We use the MS2 and Qbeta bacteriophages (diameters 27-28nm) to understand the interplay between different attraction mechanisms on nanometer-sized colloids. Small Angle X-ray Scattering (SAXS) is used to characterize the inter-particle interaction between colloidal viruses using several polymer species and different salt types.

  7. Aespoe Pillar Stability Experiment. Final coupled 3D thermo-mechanical modeling. Preliminary particle mechanical modeling

    Energy Technology Data Exchange (ETDEWEB)

    Wanne, Toivo; Johansson, Erik; Potyondy, David [Saanio and Riekkola Oy, Helsinki (Finland)

    2004-02-01

    SKB is planning to perform a large-scale pillar stability experiment called APSE (Aespoe Pillar Stability Experiment) at Aespoe HRL. The study is focused on understanding and control of progressive rock failure in hard crystalline rock and damage caused by high stresses. The elastic thermo-mechanical modeling was carried out in three dimensions because of the complex test geometry and in-situ stress tensor by using a finite-difference modeling software FLAC3D. Cracking and damage formation were modeled in the area of interest (pillar between two large scale holes) in two dimensions by using the Particle Flow Code (PFC), which is based on particle mechanics. FLAC and PFC were coupled to minimize the computer resources and the computing time. According to the modeling the initial temperature rises from 15 deg C to about 65 deg C in the pillar area during the heating period of 120 days. The rising temperature due to thermal expansion induces stresses in the pillar area and after 120 days heating the stresses have increased about 33% from the excavation induced maximum stress of 150 MPa to 200 MPa in the end of the heating period. The results from FLAC3D model showed that only regions where the crack initiation stress has exceeded were identified and they extended to about two meters down the hole wall. These could be considered the areas where damage may occur during the in-situ test. When the other hole is pressurized with a 0.8 MPa confining pressure it yields that 5 MPa more stress is needed to damage the rock than without confining pressure. This makes the damaged area in some degree smaller. High compressive stresses in addition to some tensile stresses might induce some AE (acoustic emission) activity in the upper part of the hole from the very beginning of the test and are thus potential areas where AE activities may be detected. Monitoring like acoustic emissions will be measured during the test execution. The 2D coupled PFC-FLAC modeling indicated that

  8. Dynamic Colloidal Molecules Maneuvered by Light-Controlled Janus Micromotors.

    Science.gov (United States)

    Gao, Yirong; Mou, Fangzhi; Feng, Yizheng; Che, Shengping; Li, Wei; Xu, Leilei; Guan, Jianguo

    2017-07-12

    In this work, we propose and demonstrate a dynamic colloidal molecule that is capable of moving autonomously and performing swift, reversible, and in-place assembly dissociation in a high accuracy by manipulating a TiO2/Pt Janus micromotor with light irradiation. Due to the efficient motion of the TiO2/Pt Janus motor and the light-switchable electrostatic interactions between the micromotor and colloidal particles, the colloidal particles can be captured and assembled one by one on the fly, subsequently forming into swimming colloidal molecules by mimicking space-filling models of simple molecules with central atoms. The as-demonstrated dynamic colloidal molecules have a configuration accurately controlled and stabilized by regulating the time-dependent intensity of UV light, which controls the stop-and-go motion of the colloidal molecules. The dynamic colloidal molecules are dissociated when the light irradiation is turned off due to the disappearance of light-switchable electrostatic interaction between the motor and the colloidal particles. The strategy for the assembly of dynamic colloidal molecules is applicable to various charged colloidal particles. The simulated optical properties of a dynamic colloidal molecule imply that the results here may provide a novel approach for in-place building functional microdevices, such as microlens arrays, in a swift and reversible manner.

  9. Mechanical stability study of capture cavity II at Fermilab

    Energy Technology Data Exchange (ETDEWEB)

    McGee, M.W.; Pischalnikov, Y.; /Fermilab

    2007-06-01

    Problematic resonant conditions at both 18 Hz and 180 Hz were encountered and identified early during the commissioning of Capture Cavity II (CC2) at Fermilab. CC2 consists of an external vacuum vessel and a superconducting high gradient (close to 25 MV/m) 9-cell 1.3 GHz niobium cavity, transported from DESY for use in the A0 Photoinjector at Fermilab. An ANSYS modal finite element analysis (FEA) was performed in order to isolate the source of the resonance and directed the effort towards stabilization. Using a fast piezoelectric tuner to excite (or shake) the cavity at different frequencies (from 5 Hz to 250 Hz) at a low-range sweep for analysis purposes. Both warm (300 K) and cold (1.8 K) accelerometer measurements at the cavity were taken as the resonant ''fix'' was applied. FEA results, cultural and technical noise investigation, and stabilization techniques are discussed.

  10. Sheared Flow As A Stabilizing Mechanism In Astrophysical Jets

    CERN Document Server

    Wanex, Lucas

    2008-01-01

    It has been hypothesized that the sustained narrowness observed in the asymptotic cylindrical region of bipolar outflows from Young Stellar Objects (YSO) indicates that these jets are magnetically collimated. The j cross B force observed in z-pinch plasmas is a possible explanation for these observations. However, z-pinch plasmas are subject to current driven instabilities (CDI). The interest in using z-pinches for controlled nuclear fusion has lead to an extensive theory of the stability of magnetically confined plasmas. Analytical, numerical, and experimental evidence from this field suggest that sheared flow in magnetized plasmas can reduce the growth rates of the sausage and kink instabilities. Here we propose the hypothesis that sheared helical flow can exert a similar stabilizing influence on CDI in YSO jets.

  11. Statistical mechanics provides novel insights into microtubule stability and mechanism of shrinkage.

    Science.gov (United States)

    Jain, Ishutesh; Inamdar, Mandar M; Padinhateeri, Ranjith

    2015-02-01

    Microtubules are nano-machines that grow and shrink stochastically, making use of the coupling between chemical kinetics and mechanics of its constituent protofilaments (PFs). We investigate the stability and shrinkage of microtubules taking into account inter-protofilament interactions and bending interactions of intrinsically curved PFs. Computing the free energy as a function of PF tip position, we show that the competition between curvature energy, inter-PF interaction energy and entropy leads to a rich landscape with a series of minima that repeat over a length-scale determined by the intrinsic curvature. Computing Langevin dynamics of the tip through the landscape and accounting for depolymerization, we calculate the average unzippering and shrinkage velocities of GDP protofilaments and compare them with the experimentally known results. Our analysis predicts that the strength of the inter-PF interaction (E(s)(m)) has to be comparable to the strength of the curvature energy (E(b)(m)) such that E(s)(m) - E(b)(m) ≈ 1kBT, and questions the prevalent notion that unzippering results from the domination of bending energy of curved GDP PFs. Our work demonstrates how the shape of the free energy landscape is crucial in explaining the mechanism of MT shrinkage where the unzippered PFs will fluctuate in a set of partially peeled off states and subunit dissociation will reduce the length.

  12. Statistical mechanics provides novel insights into microtubule stability and mechanism of shrinkage.

    Directory of Open Access Journals (Sweden)

    Ishutesh Jain

    2015-02-01

    Full Text Available Microtubules are nano-machines that grow and shrink stochastically, making use of the coupling between chemical kinetics and mechanics of its constituent protofilaments (PFs. We investigate the stability and shrinkage of microtubules taking into account inter-protofilament interactions and bending interactions of intrinsically curved PFs. Computing the free energy as a function of PF tip position, we show that the competition between curvature energy, inter-PF interaction energy and entropy leads to a rich landscape with a series of minima that repeat over a length-scale determined by the intrinsic curvature. Computing Langevin dynamics of the tip through the landscape and accounting for depolymerization, we calculate the average unzippering and shrinkage velocities of GDP protofilaments and compare them with the experimentally known results. Our analysis predicts that the strength of the inter-PF interaction (E(s(m has to be comparable to the strength of the curvature energy (E(b(m such that E(s(m - E(b(m ≈ 1kBT, and questions the prevalent notion that unzippering results from the domination of bending energy of curved GDP PFs. Our work demonstrates how the shape of the free energy landscape is crucial in explaining the mechanism of MT shrinkage where the unzippered PFs will fluctuate in a set of partially peeled off states and subunit dissociation will reduce the length.

  13. Formation of one-dimensional Ag-Au solid solution colloids with Au nanorods as seeds, their alloying mechanisms, and surface plasmon resonances

    Science.gov (United States)

    Guo, Tao; Tan, Yiwei

    2012-12-01

    In this work, one dimensional (1D) Ag-Au solid solution nanoalloys were synthesized by rapidly diffusing Ag into the preformed Au nanorod (AuNR) seeds at ambient temperature in aqueous solution. By varying the molar ratio of AgCl/AuNR (in gold atoms), two kinds of 1D Ag-Au alloy nanostructures with a narrow size distribution--AgAu nanowires and Ag33Au67 nanorods--could be obtained in high yields when NaCl and polyvinylpyrrolidone (PVP) were used as an additive and capping reagent, respectively. Based on HRTEM imaging combined with a series of control experiments, it is conceivable that vacancy/defect-motivated interdiffusion of Ag and Au atoms coupled with oxidative etching is a crucial stage in the mechanism responsible for this room-temperature alloying process, and the subsequent conjugation of the fused Ag-Au alloyed nanostructures is associated with the formation of the AgAu nanowires. The resulting 1D Ag-Au nanoalloys form stable colloidal dispersions and show unique localized surface plasmon resonance (LSPR) peaks in the ensemble extinction spectra.In this work, one dimensional (1D) Ag-Au solid solution nanoalloys were synthesized by rapidly diffusing Ag into the preformed Au nanorod (AuNR) seeds at ambient temperature in aqueous solution. By varying the molar ratio of AgCl/AuNR (in gold atoms), two kinds of 1D Ag-Au alloy nanostructures with a narrow size distribution--AgAu nanowires and Ag33Au67 nanorods--could be obtained in high yields when NaCl and polyvinylpyrrolidone (PVP) were used as an additive and capping reagent, respectively. Based on HRTEM imaging combined with a series of control experiments, it is conceivable that vacancy/defect-motivated interdiffusion of Ag and Au atoms coupled with oxidative etching is a crucial stage in the mechanism responsible for this room-temperature alloying process, and the subsequent conjugation of the fused Ag-Au alloyed nanostructures is associated with the formation of the AgAu nanowires. The resulting 1D Ag

  14. Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

    Science.gov (United States)

    Wen, Liang-Saw; Santschi, Peter H.; Tang, Degui

    1997-07-01

    It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority (>50%) of the colloidal trace metals had been transferred into the particulate phase (≥0.45 μm), except for 65Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe (˜60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of 59Fe and 110Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of 54Mn, 133Ba, 65Zn, 109Cd, 113Sn, and 60CO increased while the LMW (≤ 1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The values of the particle-water ( Kd) and colloid-water partitioning ( Kc) coefficients for most trace metals were similar to those observed in Galveston Bay waters, suggesting complementary results to field studies. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying

  15. [Stabilization of Cadmium Contaminated Soils by Ferric Ion Modified Attapulgite (Fe/ATP)--Characterizations and Stabilization Mechanism].

    Science.gov (United States)

    Rong, Yang; Li, Rong-bo; Zhou, Yong-li; Chen, Jing; Wang, Lin-ling; Lu, Xiao-hua

    2015-08-01

    Ferric ion modified attapulgite (Fe/ATP) was prepared by impregnation and its structure and morphology were characterized. The toxicity characteristic leaching procedure (TCLP) was used to evaluate the effect of Cadmium( Cd) stabilization in soil with the addition of attapulgite (ATP) and Fe/ATP. The stabilization mechanism of Cd was further elucidated by comparing the morphologies and structure of ATP and Fe/ATP before and after Cd adsorption. Fe/ATP exhibited much better adsorption capacity than ATP, suggesting different adsorption mechanisms occurred between ATP and Fe/ATP. The leaching concentrations of Cd in soil decreased by 45% and 91% respectively, with the addition of wt. 20% ATP and Fe/ATP. The former was attributed to the interaction between Cd2 and --OH groups by chemical binding to form inner-sphere complexes in ATP and the attachment between Cd2+ and the defect sites in ATP framework. Whereas Cd stabilization with Fe/ATP was resulted from the fact that the active centers (--OH bonds or O- sites) on ATP could react with Fe3+ giving Fe--O--Cd-- bridges, which helped stabilize Cd in surface soil. What'more, the ferric oxides and metal hydroxides on the surface of ATP could interact with Cd, probably by the formation of cadmium ferrite. In conclusion, Fe/ATP, which can be easily prepared, holds promise as a potential low-cost and environmental friendly stabilizing agent for remediation of soil contaminated with heavy metals.

  16. Efficiency of Mechanisms for Ensuring Financial Stability in Developed Countries

    Directory of Open Access Journals (Sweden)

    Mizjuk Bohdan M.

    2016-08-01

    Full Text Available The aim of the article is to identify relationships between the monetary policy and long-term financial stability. The main method of the study is retrospective analysis of macroeconomic and financial performance of the United States and other developed countries. It has been shown that neither Neo-Keynesian nor monetarist approaches are able to provide long-term financial stability under simultaneous low levels of volatility of GDP and inflation. In addition, the policy of inflation targeting in developed countries is not able to eliminate the risk of significant macro-economic recessions. The article states that the cause of the recessions is a systemic risk growth due to concentration of financial resources in the banking sector and in the hands of owners of non-financial corporations. This concentration has two effects: 1 growth of moral hazard at crediting; 2 decrease in the effective demand on the part of households. Redistribution of financial resources among different macro-economic groups of agents does not happen in a short period of time and is a result of the long-term monetary policy. Since the modern economic statistics has certain methodological problems with calculation of the Gini coefficient, such indicator as a share of wages in GDP is proposed in the article for studying the dynamics of uneven distribution of financial resources in the United States. The conducted retrospective analysis of the US monetary policy showed that an important system indicator of uniformity of financial resources distribution among macroeconomic agents falls out of sight of regulators. Distribution of macroeconomic risks depends on distribution of financial resources in the system, which determines its financial stability. The article justifies the need for developing the monetary policy methods that would simultaneously minimize the volatility of the GDP, inflation and maintain a uniform distribution of financial resources at an acceptable level.

  17. Mechanical stability of cylindrical thin-shell wormholes

    Energy Technology Data Exchange (ETDEWEB)

    Sharif, M. [University of the Punjab, Department of Mathematics, Lahore (Pakistan); Azam, M. [University of Education, Division of Science and Technology, Lahore (Pakistan)

    2013-04-15

    In this paper, we apply the cut and paste procedure to the charged black string for the construction of a thin-shell wormhole. We consider the Darmois-Israel formalism to determine the surface stresses of the shell. We take the Chaplygin gas to deal with the matter distribution on shell. The radial perturbation approach (preserving the symmetry) is used to investigate the stability of static solutions. We conclude that stable static solutions exist both for uncharged and charged black string thin-shell wormholes for particular values of the parameters. (orig.)

  18. Microfluidic colloid filtration

    Science.gov (United States)

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, Matthias

    2016-03-01

    Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.

  19. Robotic patch-stabilizer using wire driven mechanism for minimally invasive fetal surgery.

    Science.gov (United States)

    Zhang, Bo; Kobayashi, Yo; Chiba, Toshio; Fujie, Masakatsu G

    2009-01-01

    The clinical target of this study is intrauterine patch coverage of fetal myelomeningocele. We propose a new surgical robotic system for intrauterine fetal surgery with patch-stabilizer and laser manipulator. The target disease of the fetal surgery is spina bifida or myelomeningocele, which is incomplete closure in the spinal column and one of the common fetal diseases. In the fetal surgery, the collagen patch is supposed to be stabilized onto the fragile fetal tissue during the laser fixation process. In this study, a prototype of the patch-stabilizer using wire driven mechanism has been developed for precise force control on the patch without damaging fetal tissue. The diameter of the patch-stabilizer's shaft is 2.4 mm. The patch-stabilizer including one ball joint and wire driven mechanism is able to bend through 40 degrees. The stabilizing part holds collagen patch with diamond shape mechanism using wire driven. In this paper, we showed that the patch-stabilizer is developed with the stabilizing force control using the tension control of wires. Results of the experiment showed that the tension of driven wires was controlled at 0.3 N to stabilize the collagen patch onto the lesion surface without the damages of fetal tissues and the influence by the amnion liquid.

  20. Unraveling protein stabilization mechanisms : Vitrification and water replacement in a glass transition temperature controlled system

    NARCIS (Netherlands)

    Grasmeijer, N; Stankovic, M; de Waard, H; Frijlink, H W; Hinrichs, W L J

    2013-01-01

    The aim of this study was to elucidate the role of the two main mechanisms used to explain the stabilization of proteins by sugar glasses during drying and subsequent storage: the vitrification and the water replacement theory. Although in literature protein stability is often attributed to either v

  1. Theory of activated-rate processes under shear with application to shear-induced aggregation of colloids.

    Science.gov (United States)

    Zaccone, Alessio; Wu, Hua; Gentili, Daniele; Morbidelli, Massimo

    2009-11-01

    Using an approximation scheme within the convective diffusion (two-body Smoluchowski) equation framework, we unveil the shear-driven aggregation mechanism at the origin of structure formation in sheared colloidal systems. The theory, verified against numerics and experiments, explains the induction time followed by explosive (irreversible) rise of viscosity observed in charge-stabilized colloidal and protein systems under steady shear. The Arrhenius-type equation with shear derived here, extending Kramers' theory in the presence of shear, clearly demonstrates the important role of shear drive in activated-rate processes as they are encountered in soft condensed matter.

  2. Colloid-Facilitated Transport of Low-Solubility Radionuclides: A Field, Experimental, and Modeling Investigation

    Energy Technology Data Exchange (ETDEWEB)

    Kersting, A B; Reimus, P W; Abdel-Fattah, A; Allen, P G; Anghel, I; Benedict, F C; Esser, B K; Lu, N; Kung, K S; Nelson, J; Neu, M P; Reilly, S D; Smith, D K; Sylwester, E R; Wang, L; Ware, S D; Warren, RG; Williams, R W; Zavarin, M; Zhao, P

    2003-02-01

    For the last several years, the Underground Test Area (UGTA) program has funded a series of studies carried out by scientists to investigate the role of colloids in facilitating the transport of low-solubility radionuclides in groundwater, specifically plutonium (Pu). Although the studies were carried out independently, the overarching goals of these studies has been to determine if colloids in groundwater at the NTS can and will transport low-solubility radionuclides such as Pu, define the geochemical mechanisms under which this may or may not occur, determine the hydrologic parameters that may or may not enhance transport through fractures and provide recommendations for incorporating this information into future modeling efforts. The initial motivation for this work came from the observation in 1997 and 1998 by scientists from Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL) that low levels of Pu originally from the Benham underground nuclear test were detected in groundwater from two different aquifers collected from wells 1.3 km downgradient (Kersting et al., 1999). Greater than 90% of the Pu and other radionuclides were associated with the naturally occurring colloidal fraction (< 1 micron particles) in the groundwater. The colloids consisted mainly of zeolite (mordenite, clinoptilolite/heulandite), clays (illite, smectite) and cristobalite (SiO{sub 2}). These minerals were also identified as alteration mineral components in the host rock aquifer, a rhyolitic tuff. The observation that Pu can and has migrated in the subsurface at the NTS has forced a rethinking of our basic assumptions regarding the mechanical and geochemical transport pathways of low-solubility radionuclides. If colloid-facilitated transport is the primary mechanism for transporting low-solubility radionuclides in the subsurface, then current transport models based solely on solubility arguments and retardation estimates may underestimate the flux and

  3. Reliable routing mechanism based on neighbor stability for MANET

    Institute of Scientific and Technical Information of China (English)

    WU Da-peng; WU Mu-qing; ZHEN Yan

    2009-01-01

    One critical issue for routing in mobile Ad-hoc networks (MANETs) is how to select a reliable path that can last longer because mobility may cause frequent breakdown in radio links. A novel routing mechanism based on link lifetime estimation is proposed in this article. In this mechanism, the node's received signal strength is obtained continuously by using Newton interpolation polynomial, and by method of middle value and interception, the reference points are selected to estimate the link lifetime. With the constraint of link lifetime and hop counts, the source nodes set up the route hop by hop. The simulations show that link lifetime can be predicted regardless of mobility pattern. Moreover, the route discovery times and packet drop ratio can be reduced by the proposed mechanism, and thus improving the performance of MANETs.

  4. A stabilization mechanism for the low-velocity gaseous detonations with losses

    Science.gov (United States)

    Kasimov, Aslan; Sow, Aliou; Semenko, Roman

    2016-11-01

    Using the reactive Euler equations, we investigate numerically the nonlinear stability of steady-state one-dimensional gaseous detonations in the presence of both momentum and heat losses. Our results point to a possible stabilization mechanism for the low-velocity detonations in such systems. The mechanism stems from the existence of a one-parameter family of steady-state solutions found in Semenko et al..

  5. Stability mechanisms of a thermophilic laccase probed by molecular dynamics

    DEFF Research Database (Denmark)

    Christensen, Niels Johan; Kepp, Kasper Planeta

    2013-01-01

    to variable ionic strengths, temperatures, and glycosylation status. Near-physiological conditions provided excellent agreement with the crystal structure (average RMSD ∼0.92 Å) and residual agreement with experimental B-factors. The persistence of backbone hydrogen bonds was identified as a key descriptor...... of structural response to environment, whereas solvent-accessibility, radius of gyration, and fluctuations were only locally relevant. Backbone hydrogen bonds decreased systematically with temperature in all simulations (∼9 per 50 K), probing structural changes associated with enthalpy-entropy compensation....... Approaching T opt (∼350 K) from 300 K, this change correlated with a beginning "unzipping" of critical β-sheets. 0 M ionic strength triggered partial denucleation of the C-terminal (known experimentally to be sensitive) at 400 K, suggesting a general salt stabilization effect. In contrast, F(-) (but not Cl...

  6. Stability Conditions and Mechanism of Cream Soaps: Effect of Polyols.

    Science.gov (United States)

    Sagitani, Hiromichi; Komoriya, Masumi

    2015-01-01

    Fatty acids, fatty acid potassium soaps, polyols and water are essential ingredients for producing stable cream soaps. The solution behavior of the above four components system has been studied to elucidate the effect of four sorts of polyols (glycerol, 1,3-butylene glycol, polyethylene glycol 400 and dipropylene glycol) on the stability of cream soaps. It has been revealed that the lamellar liquid crystalline one-phase converted to a two-phase of a lamellar phase and an isotropic aqueous solution by the addition of a few percent of 1,3-butylene glycol, polyethylene glycol 400 and dipropylene glycol, whereas the lamellar one-phase was remained by about 50 wt% of glycerol in the aqueous solution. The X-ray data at room temperature showed that the existence of 1:1 acid soap (1:1 mole ratio of potassium soap/fatty acid) crystals in the 1,3-butylene glycol, polyethylene glycol 400 and dipropylene glycol systems, whereas that the coexistence of 1:1 acid soap crystal and a lamellar gel phase (swelled lamellar gel structure) in the glycerol system. The phase transition peaks from coagel to gel (Tgel) and from gel to liquid state (Tc) were appeared in the above four polyol systems by DSC measurements. It was confirmed from the combined data of SAXS and DSC that the existence of anhydrous 1:1 acid soap gels (or with small amount of bound water) in the all polyol systems, whereas the coexistence of the anhydrate gel and the swelled gel with a lot of intermediate water in the only glycerol system. This swelled gel structure would be contributed to stabilize the dispersed anhydrate acid soap crystals in cream soaps.

  7. Disturbance Observers for Rigid Mechanical Systems: Equivalence, Stability, and Design

    NARCIS (Netherlands)

    Schrijver, Erwin; Dijk, van Johannes

    2002-01-01

    Mechanical (direct-drive) systems designed for high-speed and high-accuracy applications require control systems that eliminate the influence of disturbances like cogging forces and friction. One way to achieve additional disturbance rejection is to extend the usual (P(I)D) controller with a disturb

  8. Mechanism of stability development of machine building enterprises

    Directory of Open Access Journals (Sweden)

    Andriу Vasylyuk

    2013-05-01

    Full Text Available Based on the correlation relationships between investment, output, average wage growth mechanism is investigated as a potential domestic investment, production and employment potential. It is shown that economic growth is possible with maximum use of internal resources, investments, domestic market development, leasing, such as the outsourcing of equipment and personnel

  9. Cyclic stretch-bending: mechanics, stability and formability

    NARCIS (Netherlands)

    Emmens, W.C.; van den Boogaard, Antonius H.

    2011-01-01

    Cyclic stretch-bending has been studied using the so-called Continuous-Bending-under-Tension (CBT) test. This is a modified tensile test where the specimen is subjected to repetitive bending at the same time. A wide variety of materials have been tested this way. A simple mechanical model is

  10. Cholesterol increases kinetic, energetic, and mechanical stability of the human β2-adrenergic receptor

    DEFF Research Database (Denmark)

    Zocher, Michael; Zhang, Cheng; Rasmussen, Søren Gøgsig Faarup;

    2012-01-01

    the kinetic, energetic, and mechanical stability of almost every structural segment at sufficient magnitude to alter the structure and functional relationship of β(2)AR. One exception was the structural core segment of β(2)AR, which establishes multiple ligand binding sites, and its properties were...... to quantify the mechanical strength and flexibility, conformational variability, and kinetic and energetic stability of structural segments stabilizing the human β(2)-adrenergic receptor (β(2)AR) in the absence and presence of the cholesterol analog cholesteryl hemisuccinate (CHS). CHS considerably increased...

  11. A unified mechanism for the stability of surface nanobubbles: contact line pinning and supersaturation.

    Science.gov (United States)

    Liu, Yawei; Zhang, Xianren

    2014-10-07

    In this paper, we apply the molecular dynamics simulation method to study the stability of surface nanobubbles in both pure fluids and gas-liquid mixtures. First, we demonstrate with molecular simulations, for the first time, that surface nanobubbles can be stabilized in superheated or gas supersaturated liquid by the contact line pinning caused by the surface heterogeneity. Then, a unified mechanism for nanobubble stability is put forward here that stabilizing nanobubbles require both the contact line pinning and supersaturation. In the mechanism, the supersaturation refers to superheating for pure fluids and gas supersaturation or superheating for the gas-liquid mixtures, both of which exert the same effect on nanobubble stability. As the level of supersaturation increases, we found a Wenzel or Cassie wetting state for undersaturated and saturated fluids, stable nanobubbles at moderate supersaturation with decreasing curvature radius and contact angle, and finally the liquid-to-vapor phase transition at high supersaturation.

  12. LONG-TERM COLLOID MOBILIZATION AND COLLOID-FACILITATED TRANSPORT OF RADIONUCLIDES IN A SEMI-ARID VADOSE ZONE

    Energy Technology Data Exchange (ETDEWEB)

    Markus Flury; James B. Harsh; Fred Zhang; Glendon W. Gee; Earl D. Mattson; Peter C. L

    2012-08-01

    The main purpose of this project was to improve the fundamental mechanistic understanding and quantification of long-term colloid mobilization and colloid-facilitated transport of radionuclides in the vadose zone, with special emphasis on the semi-arid Hanford site. While we focused some of the experiments on hydrogeological and geochemical conditions of the Hanford site, many of our results apply to colloid and colloid-facilitated transport in general. Specific objectives were (1) to determine the mechanisms of colloid mobilization and colloid-facilitated radionuclide transport in undisturbed Hanford sediments under unsaturated flow, (2) to quantify in situ colloid mobilization and colloid-facilitated radionuclidetransport from Hanford sediments under field conditions, and (3) to develop a field-scale conceptual and numerical model for colloid mobilization and transport at the Hanford vadose zone, and use that model to predict long-term colloid and colloid- facilitated radionuclide transport. To achieve these goals and objectives, we have used a combination of experimental, theoretical, and numerical methods at different spatial scales, ranging from microscopic investigationsof single particle attachment and detachment to larger-scale field experiments using outdoor lysimeters at the Hanford site. Microscopic and single particle investigations provided fundamental insight into mechanisms of colloid interactions with the air-water interface. We could show that a moving air water interface (such as a moving water front during infiltration and drainage) is very effective in removing and mobilizing particles from a stationary surface. We further demonstrated that it is particularly the advancing air-water interface which is mainly responsible for colloid mobilization. Forces acting on the colloids calculated from theory corroborated our experimental results, and confirm that the detachment forces (surface tension forces) during the advancing air-water interface

  13. Two-substrate vertical deposition for stable colloidal crystal chips

    Institute of Scientific and Technical Information of China (English)

    CHEN Xin; SUN Zhiqiang; CHEN Zhimin; ZHANG Kai; YANG Bai

    2005-01-01

    By combining vertical deposition with micromolding in capillaries method, we have demonstrated the two-substrate vertical deposition, an alternative and versatile procedure for fabricating high-quality stable colloidal crystal chips. Apparent bright colors, special UV-vis spectra, scanning electron microscopy (SEM) and atomic force microscopy (AFM) images all prove that high-quality colloidal crystal structures are formed in between the two substrates. During the two-substrate vertical deposition for colloidal crystal chips, capillary force and evaporation of the medium are critical to the formation of the colloidal crystals; while the confinement in between two close substrates makes the resulting colloidal crystal chips more stable. Due to the excellent stability, these colloidal crystal chips can be used to construct some composite optical devices via a simpler and more flexible process. Meanwhile, they can also be further used as the templates for ordered multiporous materials.

  14. Gel trapping of dense colloids.

    Science.gov (United States)

    Laxton, Peter B; Berg, John C

    2005-05-01

    Phase density differences in sols, foams, or emulsions often lead to sedimentation or creaming, causing problems for materials where spatial uniformity over extended periods of time is essential. The problem may be addressed through the use of rheology modifiers in the continuous phase. Weak polymer gels have found use for this purpose in the food industry where they appear to be capable of trapping dispersoid particles in a three-dimensional matrix while displaying water-like viscosities at low shear. Attempts to predict sedimentation stability in terms of particle properties (size, shape, density difference) and gel yield stress have led to qualitative success for suspensions of large particles. The effect of particle size, however, in particular the case in which colloidal dimensions are approached, has not been investigated. The present work seeks to determine useful stability criteria for colloidal dispersions in terms of readily accessible viscoelastic descriptors. Results are reported for systems consisting of 12 microm poly(methyl methacrylate) (PMMA) spheres dispersed in aqueous gellan gum. Monovalent salt concentration is varied to control rheological properties, and sedimentation/centrifugation experiments are performed to determine dispersion stability. Necessary conditions for stability consist of a minimum yield stress together with a value of tan delta less than unity.

  15. Structural and mechanical stability of rare-earth diborides

    Institute of Scientific and Technical Information of China (English)

    Haci Ozisik; Engin Deligoz; Kemal Colakoglu; Gokhan Surucu

    2013-01-01

    Structural and mechanical properties of several rare-earth diborides were systematically investigated by first principles calculations.Specifically,we studied XB2,where X =Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,and Lu in the hexagonal A1B2,ReB2,and orthorhombic OsB2-type structures.The lattice parameters,bulk modulus,bond distances,second order elastic constants,and related polycrystalline elastic moduli (e.g.,shear modulus,Young's modulus,Poisson's ratio,Debye temperature,sound velocities) were calculated.Our results indicate that these compounds are mechanically stable in the considered structures,and according to "Chen's method",the predicted Vickers hardness shows that they are hard materials in A1B2-and OsB2-type structures.

  16. Mobility and equilibrium stability analysis of pin-jointed mechanisms with equilibrium matrix SVD

    Institute of Scientific and Technical Information of China (English)

    LU Jin-yu; LUO Yao-zhi; LI Na

    2007-01-01

    Under certain load pattern, the geometrically indeterminate pin-jointed mechanisms will present certain shapes to keep static equalization. This paper proposes a matrix-based method to determine the mobility and equilibrium stability of mechanisms according to the effects of the external loads. The first and second variations of the potential energy function of mechanisms under conservative force field are analyzed. Based on the singular value decomposition (SVD) method, a new criterion for the mobility and equilibrium stability of mechanisms can be concluded by analyzing the equilibrium matrix. The mobility and stability of mechanisms can be classified by unified matrix formulae. A number of examples are given to demonstrate the proposed criterion. In the end, criteria are summarized in a table.

  17. Stabilization mechanisms for information stored in magnetic nanowire arrays

    Science.gov (United States)

    Cisternas, Eduardo; Faúndez, Julián; Vogel, Eugenio E.

    2017-03-01

    The durability of the stored information in magnetic systems is one important feature in firmware applications such as security codes, magnetic keys and other similar products. In the present paper we discuss two different ways of preserving patterns in the set of magnetic wires trapped in the porous membranes used to produce them. One of the techniques is the inscription of an opposite magnetic band of about 1/3 the width of the stored pattern which minimizes the repulsive energy among the ferromagnetic cylinders still leaving a potent magnetic signal to be read. The other technique makes use of segmented nanowires which present a competition of repulsive energy of segments within the same layer while the interaction is attractive with the closer segments of the other layer; such a competition can lead to stabilization if the geometrical parameters are properly controlled. The first technique is cheaper and faster to implement, while the second technique needs a more complete fabrication process but can lead to more durable stored information.

  18. Lidov-Kozai Mechanism in Hydrodynamical Disks: Linear Stability Analysis

    Science.gov (United States)

    Zanazzi, J. J.; Lai, Dong

    2017-01-01

    Recent SPH simulations by Martin et al. (2014) suggest a circumstellar gaseous disk may exhibit coherent eccentricity-inclination oscillations due to the tidal forcing of an inclined binary companion, in a manner that resembles Lidov-Kozai oscillations in hierarchical triple systems. We carry out linear stability analysis for the eccentricity growth of circumstellar disks in binaries, including the effects of gas pressure and viscosity and secular (orbital-averaged) tidal force from the inclined companion. We find that the growth of disk eccentricity depends on the dimensionless ratio (S) between c_s^2 (the disk sound speed squared) and the tidal torque acting on the disk (per unit mass) from the companion. For S ≪ 1, the standard Lidov-Kozai result is recovered for a thin disk annulus: eccentricity excitation occurs when the mutual inclination I between the disk and binary lies between 39° and 141°. As S increases, the inclination window for eccentricity growth generally becomes narrower. For S ≳ a few, eccentricity growth is suppressed for all inclination angles. Surprisingly, we find that for S ˜ 1 and certain disk density/pressure profiles, eccentricity excitation can occur even when I is much less than 39°.

  19. Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

    Energy Technology Data Exchange (ETDEWEB)

    Wen, L.S.; Santschi, P.H.; Tang, D. [Texas A & M Univ., Galveston, TX (United States)

    1997-07-01

    It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority ( >50%) of the colloidal trace metals had been transferred into the particulate phase ({ge} 0.45{mu}m), except for {sup 65}Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe ({approximately}60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of {sup 59}Fe and {sup 110}Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of {sup 54}Mn, {sup 133}Ba, {sup 65}Zn, {sup 109}Cd, {sup 113}Sn, and {sup 60}Co increased while the LMW({le}1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying affinities for different trace metals. 39 refs., 8 figs., 3 tabs.

  20. Complex coacervation between colloidal silica and polyacrylamide

    Energy Technology Data Exchange (ETDEWEB)

    Kawase, Kaoru; Sakami, Hiroshi; Hayakawa, Kiyoshi

    1989-03-01

    Complex coacervation introduced by gamma-ray induced polymerization of acrylamide in colloidal silica was studied. The complex coaservate was formed by polymerization of acrylamide dissolved in a colloidal silica and methanol mixture. Complex coacervation (two-phase separation of the mixture) was observed only when the concentration of methanol was between 33 and 41 percent by volume, and the concentration of colloidal silica did not affect it. Although two phase separation was not influenced by pH change, the content of polyacrylamide was bigger in the equilibrated solution in acidic regions. It was, however, bigger in the complex coacervate at neutral and in alkaline regions. The content of polyacrylamide was also calculated from the particle diameter of complex coacervate measured by small angle X-ray scattering, and the result was well coincided with the analytical result. The stability of the complex coacervate against the addition of salts was better than that of the untreated colloidal silica. The rate of electrophoretic transport of the complex coacervate was also lower than that of the colloidal silica. From these observation it was concluded that the hydrophobic colloidal silica particles were protected by the surrounding hydrophilic polyacrylamide. (author).

  1. Karst Collapse Mechanism and Criterion for Its Stability

    Institute of Scientific and Technical Information of China (English)

    贺可强; 刘长礼; 王思敬

    2001-01-01

    Karst collapse, caused by natural or artificial abstraction of groundwater, has been a focus of environmental geological problems for its ever-increasing hazardousness. The potential erosion theory and vacuum suction erosion theory,which reveal the origin of karst collapse macroscopically, are popularly accepted. However, a mathematic prediction criterion for karst collapse cannot be established only by these two theories. From a new perspective, this paper attempts to explain the microcosmic mechanism of karst collapse on the basis of these two theories. When the shear stress surpasses the shear strength of soil, a certain point or a certain plane in the unconsolidated soil covering karst caves will fail under the mechanical effects of water and air as well as its load-pressure, and with the increase of damaged points, a breaking plane appears and the soil on karst caves is completely damaged; as a result, the karst ground collapses. On the basis of the MohrCoulomb failure theory and previous studies, the paper presents a prediction criterion of karst collapse. Finally, by taking,for example, nine typical cases of collapse caused by pumping tests in Guizhou, the paper gives the calculation process of the model and proves its reliability.``

  2. Preparation of (non-)aqueous dispersins of colloidal boehmite needles

    NARCIS (Netherlands)

    Buining, P.A.; Pathmamanoharan, C.; Philipse, A.P.; Lekkerkerker, H.N.W.

    1993-01-01

    A novel hydrothermal alkoxide method is presented for the preparation of stable, aqueousdispersions of fairly monodisperse, charged colloidal boehmite needles. A polymer coating procedure for the needles is described which leads to sterically stabilized dispersions in organic solvents.

  3. Synthesis and characterization of colloidal fluorescent silver nanoclusters.

    Science.gov (United States)

    Huang, Sherry; Pfeiffer, Christian; Hollmann, Jana; Friede, Sebastian; Chen, Justin Jin-Ching; Beyer, Andreas; Haas, Benedikt; Volz, Kerstin; Heimbrodt, Wolfram; Montenegro Martos, Jose Maria; Chang, Walter; Parak, Wolfgang J

    2012-06-19

    Ultrasmall water-soluble silver nanoclusters are synthesized, and their properties are investigated. The silver nanoclusters have high colloidal stability and show fluorescence in the red. This demonstrates that like gold nanoclusters also silver nanoclusters can be fluorescent.

  4. Lyotropic hexagonal columnar liquid crystals of large colloidal gibbsite platelets

    NARCIS (Netherlands)

    Mourad, M.C.D.; Petukhov, A.V.; Vroege, G.J.; Lekkerkerker, H.N.W.

    2010-01-01

    We report the formation of hexagonal columnar liquid crystal phases in suspensions of large (570 nm diameter), sterically stabilized, colloidal gibbsite platelets in organic solvent. In thin cells these systems display strong iridescence originating from hexagonally arranged columns that are

  5. Colloid process engineering

    CERN Document Server

    Peukert, Wolfgang; Rehage, Heinz; Schuchmann, Heike

    2015-01-01

    This book deals with colloidal systems in technical processes and the influence of colloidal systems by technical processes. It explores how new measurement capabilities can offer the potential for a dynamic development of scientific and engineering, and examines the origin of colloidal systems and its use for new products. The future challenges to colloidal process engineering are the development of appropriate equipment and processes for the production and obtainment of multi-phase structures and energetic interactions in market-relevant quantities. The book explores the relevant processes and for controlled production and how they can be used across all scales.

  6. Colloid Transport and Retention

    DEFF Research Database (Denmark)

    Yuan, Hao; Shapiro, Alexander

    2012-01-01

    different colloidal materials and their applications in chemistry, physics, biological, medical sciences and environment. Graduate students, academic and industrial researchers and medical professionals will discover recently developed colloidal materials and their applications in many areas of human......Book Description: Colloidal science and technology is one of the fastest growing research and technology areas. This book explores the cutting edge research in colloidal science and technology that will be usefull in almost every aspect of modern society. This book has a depth of information...

  7. Novel platinum black electroplating technique improving mechanical stability.

    Science.gov (United States)

    Kim, Raeyoung; Nam, Yoonkey

    2013-01-01

    Platinum black microelectrodes are widely used as an effective neural signal recording sensor. The simple fabrication process, high quality signal recording and proper biocompatibility are the main advantages of platinum black microelectrodes. When microelectrodes are exposed to actual biological system, various physical stimuli are applied. However, the porous structure of platinum black is vulnerable to external stimuli and destroyed easily. The impedance level of the microelectrode increases when the microelectrodes are damaged resulting in decreased recording performance. In this study, we developed mechanically stable platinum black microelectrodes by adding polydopamine. The polydopamine layer was added between the platinum black structures by electrodeposition method. The initial impedance level of platinum black only microelectrodes and polydopamine added microelectrodes were similar but after applying ultrasonication the impedance value dramatically increased for platinum black only microelectrodes, whereas polydopamine added microelectrodes showed little increase which were nearly retained initial values. Polydopamine added platinum black microelectrodes are expected to extend the availability as neural sensors.

  8. Mechanical Stability of Flexible Graphene-Based Displays.

    Science.gov (United States)

    Anagnostopoulos, George; Pappas, Panagiotis-Nektarios; Li, Zheling; Kinloch, Ian A; Young, Robert J; Novoselov, Kostya S; Lu, Ching Yu; Pugno, Nicola; Parthenios, John; Galiotis, Costas; Papagelis, Konstantinos

    2016-08-31

    The mechanical behavior of a prototype touch panel display, which consists of two layers of CVD graphene embedded into PET films, is investigated in tension and under contact-stress dynamic loading. In both cases, laser Raman spectroscopy was employed to assess the stress transfer efficiency of the embedded graphene layers. The tensile behavior was found to be governed by the "island-like" microstructure of the CVD graphene, and the stress transfer efficiency was dependent on the size of graphene "islands" but also on the yielding behavior of PET at relatively high strains. Finally, the fatigue tests, which simulate real operation conditions, showed that the maximum temperature gradient developed at the point of "finger" contact after 80 000 cycles does not exceed the glass transition temperature of the PET matrix. The effect of these results on future product development and the design of new graphene-based displays are discussed.

  9. Thermophoresis of charged colloidal particles.

    Science.gov (United States)

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-04-01

    Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  10. Thermophoresis of charged colloidal particles

    OpenAIRE

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-01-01

    International audience; Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  11. Mechanical stability of roll-to-roll printed solar cells under cyclic bending and torsion

    DEFF Research Database (Denmark)

    Finn, Mickey; Martens, Christian James; Zaretski, Aliaksandr V.

    2018-01-01

    The ability of printed organic solar cells (OSCs) to survive repeated mechanical deformation is critical to large-scale implementation. This paper reports an investigation into the mechanical stability of OSCs through bending and torsion testing of whole printed modules. Two types of modules...

  12. Stability analysis of finite difference schemes for quantum mechanical equations of motion

    Science.gov (United States)

    Chattaraj, P. K.; Deb, B. M.; Koneru, S. Rao

    1987-10-01

    For a pdf involving both space and time variables, stability criteria are presently shown to change drastically when the equation contains i, as in the quantum-mechanical equations of motion. It is further noted that the stability of finite difference schemes for quantum-mechanical equations of motion depends on both spatial and temporal zoning. It is possible to compare a free particle Green's function to the solution of a simple diffusion equation, and the quantum-mechanical motion of a free particle to Fresnel diffraction in optics.

  13. Colloidal stability of Ni(OH){sub 2} in water and its dispersion into a ceramic matrix from the reaction media to obtain Ni/Al{sub 2}O{sub 3} materials

    Energy Technology Data Exchange (ETDEWEB)

    Cabanas-Polo, S.; Ferrari, B.; Sanchez-Herencia, A. J.

    2014-07-01

    Ni/Al{sub 2}O{sub 3} composites have been fabricated by slip casting of concentrated Ni(OH){sub 2}/Al{sub 2}O{sub 3} suspensions and subsequent in situ reduction to metallic nickel during sintering. For that, the synthesis assisted by ultrasound of both α- and β-Ni(OH){sub 2} polymorphs, as well as their colloidal stability, have been studied. The structural differences between both polymorphs have been thoroughly studied by means of XRD, FTIR, DTA-TG, SSA, SEM and TEM, in order to optimize the starting suspensions. This way, the IEP of both polymorphs have been established (9.7 y 12 for β- and α-Ni(OH){sub 2}, respectively), as well as the optimal content of an anionic dispersant (PAA) to stabilize the particles (0.8 wt. % for beta phase and 3.0 wt. % for alpha phase). Three different Ni/Al{sub 2}O{sub 3} composites, with a high dispersion degree of the metallic phase, have been obtained considering the potential vs. particles distance curve of the Ni(OH){sub 2}, and their structure has been discussed in terms of the strength of the agglomerates and/or aggregates of the Ni(OH){sub 2}. (Author)

  14. Fundamental Studies of Fluid Mechanics: Stability in Porous Media

    Energy Technology Data Exchange (ETDEWEB)

    George M. Homsy

    2005-04-28

    This work has been concerned with theoretical, computational and experimental studies of a variety of flow and transport problems that are of generic interest and applicability in energy-related and energy-intensive processes. These include the following. (1) Problems associated with oil recovery: the global economy continues to be dependent on the stable and predictable supply of oil and fossil fuels. This will remain the case for the near term, as current estimates are that world production of oil will peak between 2025 and 2100, depending on assumptions regarding growth. Most of these resources reside in porous rocks and other naturally occurring media. Studies of flow-induced instabilities are relevant to the areas of secondary and enhanced oil recovery. (2) Small scale and Stokes flows: flows in microgeometries and involving interfaces and surfactants are of interest in a myriad of energy-related contexts. These include: pore-level modeling of the fundamental processes by which oil held in porous materials is mobilized and produced; heating and cooling energy cycles involving significant expenditure of energy in conditioning of human environments, heat pipes, and compact heat exchangers; and energy efficiency in large scale separation processes such as distillation and absorption-processes that underlie the chemical process industries. (3) Coating flows: these are of interest in information technologies, including the manufacture of integrated circuits and data storage and retrieval devices. It is estimated that 50-70% of the starting raw materials and intermediate devices in information technology processes must be discarded as a result of imperfections and failure to meet specifications. These in turn are often the result of the inability to control fluid-mechanical processes and flow instabilities. Our work over the grant period is primarily fundamental in nature. We are interested in establishing general principles and behaviors that relate to a variety of

  15. Stability of the lumbar spine. A study in mechanical engineering.

    Science.gov (United States)

    Bergmark, A

    1989-01-01

    From the mechanical point of view the spinal system is highly complex, containing a multitude of components, passive and active. In fact, even if the active components (the muscles) were exchanged by passive springs, the total number of elements considerably exceeds the minimum needed to maintain static equilibrium. In other words, the system is statically highly indeterminate. The particular role of the active components at static equilibrium is to enable a virtually arbitrary choice of posture, independent of the distribution and magnitude of the outer load albeit within physiological limits. Simultaneously this implies that ordinary procedures known from the analysis of mechanical systems with passive components cannot be applied. Hence the distribution of the forces over the different elements is not uniquely determined. Consequently nervous control of the force distribution over the muscles is needed, but little is known about how this achieved. This lack of knowledge implies great difficulties at numerical simulation of equilibrium states of the spinal system. These difficulties remain even if considerable reductions are made, such as the assumption that the thoracic cage behaves like a rigid body. A particularly useful point of view about the main principles of the force distributions appears to be the distinction between a local and a global system of muscles engaged in the equilibrium of the lumbar spine. The local system consists of muscles with insertion or origin (or both) at lumbar vertebrae, whereas the global system consists of muscles with origin on the pelvis and insertions on the thoracic cage. Given the posture of the lumbar spine, the force distribution over the local system appears to be essentially independent of the outer load of the body (though the force magnitudes are, of course, dependent on the magnitude of this load). Instead different distributions of the outer load on the body are met by different distributions of the forces in the

  16. Self-pinning by colloids confined at a contact line

    Science.gov (United States)

    Weon, Byung; Je, Jung

    2013-03-01

    Colloidal particles suspended in a fluid usually inhibit complete wetting of the fluid on a solid surface and cause pinning of the contact line, known as self-pinning. We show differences in spreading and drying behaviors of pure and colloidal droplets using optical and confocal imaging methods. These differences come from spreading inhibition by colloids confined at a contact line. We propose a self-pinning mechanism based on spreading inhibition by colloids. We find a good agreement between the mechanism and the experimental result taken by directly tracking individual colloids near the contact lines of evaporating colloidal droplets. This research was supported by the Creative Research Initiatives (Functional X-ray Imaging) of MEST/NRF.

  17. Properties and Mechanism of CFBC Fly Ash-cement based Stabilizers for Lake Sludge

    Institute of Scientific and Technical Information of China (English)

    TANG Hua; LIXiangguo; LI Menglei; SONG Liuqing; WU Zhenjun; XU Haixing

    2012-01-01

    Circulating fluidized bed combustion (CFBC) fly ash was mixed with cement or lime at a different ratio as a stabilizer to stabilize lake sludge.In order to understand the influences of stabilizers on the lake sludge properties,tests unconfined compressive strength,water stability and SEM observation were performed.The experimental results show that with the increase of the curing time,the strength of all the stabilized specimens increase,especially the samples containing cement.The strength of the specimens is decreased with the increasing of the CFBC fly ash/cement ratio,the optimum ratio between CFBC fly ash and cement is 2:3.The water stability of CFBC fly ash-cement based stabilizers is higher than those of cement and lime.Moreover,the lake sludge stabilization mechanism of CFBC fly ash-cement based stabilizers includes gelation and filling of the hydration products,i e,C-S-H gel and the AFt crystal,which act as benders to solidify those particles together and fill in the packing void of the aggregates.

  18. Trans-Planckian fluctuations and the stability of quantum mechanics

    CERN Document Server

    Valentini, Antony

    2014-01-01

    We present arguments suggesting that deviations from the Born probability rule could be generated for trans-Planckian field modes during inflation. Such deviations are theoretically possible in the de Broglie-Bohm pilot-wave formulation of quantum mechanics, according to which the Born rule describes a state of statistical equilibrium. We suggest that a stable equilibrium state can exist only in restricted conditions: on a classical background spacetime that is globally hyperbolic or in a mild quantum-gravity regime in which there is an effective Schr\\"odinger equation with a well-defined time parameter. These arguments suggest that quantum equilibrium will be unstable at the Planck scale. We construct a model in which quantum nonequilibrium is generated by a time-dependent regulator for pilot-wave dynamics, where the regulator is introduced to eliminate phase singularities. Applying our model to trans-Planckian modes that exit the Planck radius, we calculate the corrected primordial power spectrum and show t...

  19. Novel silicon allotropes: Stability, mechanical, and electronic properties

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Qingyang; Chai, Changchun; Zhao, Yingbo; Yang, Yintang; Yu, Xinhai; Liu, Yang; Zhang, Junqin [Key Laboratory of Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China); Wei, Qun, E-mail: weiaqun@163.com; Yao, Ronghui [School of Physics and Optoelectronic Engineering, Xidian University, Xi' an 710071 (China); Yan, Haiyan [College of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji 721013 (China); Xing, Mengjiang [Faculty of Information Engineering and Automation, Kunming University of Science and Technology, Kunming 650051 (China)

    2015-11-14

    One quasi-direct gap phase (Amm2) and three indirect gap phases (C2/m-16, C2/m-20, and I-4) of silicon allotropes are proposed. The detailed theoretical study on the structure, density of states, elastic properties, sound velocities, and Debye temperature of these four phases is carried out by using first principles calculations. The elastic constants of these four phases are calculated by strain-stress method. The elastic constants and the phonon calculations manifest all novel silicon allotropes in this paper are mechanically and dynamically stable at ambient condition. The B/G values indicate that these four phases of silicon are brittle materials at ambient pressure. The anisotropy properties show that C2/m-20 phase exhibits a larger anisotropy in its elastic modulus, shear elastic anisotropic factors, and several anisotropic indices than others. We have found that the Debye temperature of the four novel silicon allotropes gradually reduces in the order of C2/m-20 > Amm2 > C2/m-16 > I-4 at ambient pressure.

  20. Deformation Mechanism and Stability of a Rocky Slope

    Institute of Scientific and Technical Information of China (English)

    Huang Runqiu; Xiao Huabo; Ju Nengpan; Zhao Jianjun

    2007-01-01

    A high slope is located on the side of the spillway at a hydropower station in Southwest China, which has some weak inter-layers inclining outwards. Parts of the slope show heavy weathering and unloading. There appeared deformation and tensile crack either on the surface or on the afteredge of the slope during excavation, and under a platform (elev. 488 m), two levels of slopes collapsed on the downriver side. Based on the investigation in situ and the analysis of the geological structure, the conceptual model of deformation and failure mechanism was erected for this slope. Furthermore, the deformation characteristics were studied with FLAC3D numerical simulation. Comprehensive analysis shows that the whole deformation of the slope is unloading rebound in certain depth scope and the whole body does not slide along any weak interlayer. In addition, two parts with prominent local deformation in the shallow layer of the slope show the models of "creep sliding-tensile cracking" and "sliding-tensile cracking", respectively. Based on the above analysis, the corresponding project of support and reinforcement is proposed to make the slope more stable.

  1. One-pot synthesis of stable colloidal solutions of MFe{sub 2}O{sub 4} nanoparticles using oleylamine as solvent and stabilizer

    Energy Technology Data Exchange (ETDEWEB)

    Pérez-Mirabet, Leonardo [Departament de Química, Universitat Autònoma de Barcelona, Campus de la UAB, 08193 Bellaterra (Spain); Solano, Eduardo, E-mail: eduardo.solano@uab.cat [Departament de Química, Universitat Autònoma de Barcelona, Campus de la UAB, 08193 Bellaterra (Spain); Martínez-Julián, Fernando; Guzmán, Roger [Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra (Spain); Arbiol, Jordi [Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra (Spain); Institució Catalana de Recerca i Estudis Avançats (ICREA), 08019 Barcelona (Spain); Puig, Teresa; Obradors, Xavier; Pomar, Alberto [Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra (Spain); Yáñez, Ramón; Ros, Josep [Departament de Química, Universitat Autònoma de Barcelona, Campus de la UAB, 08193 Bellaterra (Spain); Ricart, Susagna [Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra (Spain)

    2013-03-15

    Highlights: ► One-pot synthesis of ferrite magnetic nanoparticles (<10 nm) in non-polar media. ► Nanoparticles present high monocrystal quality and monodispersion. ► Superparamagnetic behavior at room temperature. ► Nanoparticles transfer to polar media via ligand exchange. - Abstract: An easy, efficient, reproducible and scalable one-pot synthetic methodology to obtain magnetic spinel ferrite nanoparticles has been developed. This approach is based on one-pot thermal decomposition of Fe(acac){sub 3} and M(acac){sub 2} (M = Co, Mn, Cu and Zn) in oleylamine, which also acts as a capping ligand, by producing stable colloidal dispersions of nanoparticles in non-polar solvents. The properties of the nanoparticles have been studied via different techniques, such as transmission electron microscopy, which shows that nanoparticles are monocrystallines and a narrow dispersion in size; magnetic analyses have demonstrated that the resulting ferrite nanoparticles show high saturation values and superparamagnetic behavior at room temperature; X-ray diffraction has also been performed, and it confirms that the synthesized nanoparticles have a spinel structure. Complementarily, ligand exchange has been also carried out in order to produce dispersions of the synthesized nanoparticles in polar media.

  2. Specific detection of cysteine and homocysteine in biological fluids by tuning the pH values of fluorosurfactant-stabilized gold colloidal solution.

    Science.gov (United States)

    Xiao, Qunyan; Shang, Fei; Xu, Xuechen; Li, Qianqian; Lu, Chao; Lin, Jin-Ming

    2011-12-15

    This study describes the use of 14 nm nonionic fluorosurfactant-capped gold nanoparticles (FSN-capped AuNPs) for the simultaneous detection of cysteine (Cys) and homocysteine (Hcy) using colorimetric method, requiring no use of separation techniques. It was found that the kinetics of Cys/Hcy-induced aggregation of the 14 nm FSN-capped AuNPs strongly depends on the pH value of gold colloidal solution. At a pH of 6.5, the Cys-induced aggregation kinetics of the FSN-capped AuNPs was almost identical to that induced by Hcy, facilitating simultaneous detection of total Cys and Hcy up to a concentration as low as 0.15 μM; while at pH 12.0, the kinetics of Cys-induced aggregation was much faster than that inducted by Hcy, leading to selective detection of Cys at concentration as low as 1.0 μM in the presence of Hcy. The applicability of the method was validated by spiking known amount of Cys and Hcy in human urine and plasma samples, obtaining a recovery of 95.4-105.5%. The present approach is simple, high selective and provides high reproducibility, and has a great potentiality in disease diagnosis.

  3. Metal-oxide-metal point contact junction detectors. [detection mechanism and mechanical stability

    Science.gov (United States)

    Baird, J.; Havemann, R. H.; Fults, R. D.

    1973-01-01

    The detection mechanism(s) and design of a mechanically stable metal-oxide-metal point contact junction detector are considered. A prototype for a mechanically stable device has been constructed and tested. A technique has been developed which accurately predicts microwave video detector and heterodyne mixer SIM (semiconductor-insulator-metal) diode performance from low dc frequency volt-ampere curves. The difference in contact potential between the two metals and geometrically induced rectification constitute the detection mechanisms.

  4. Manipulation of colloidal crystallization

    NARCIS (Netherlands)

    Vermolen, E.C.M.

    2008-01-01

    Colloidal particles (approximately a micrometer in diameter) that are dispersed in a fluid, behave thermodynamically similar to atoms and molecules: at low concentrations they form a fluid, while at high concentrations they can crystallize into a colloidal crystal to gain entropy. The analogy with m

  5. Multiple Resonance and Stability of a Motor-elastic Linkage Mechanism System

    Institute of Scientific and Technical Information of China (English)

    LI Zhao-jun; CAI Gan-wei; DAI Wen-zheng

    2006-01-01

    The dynamics of a three-phase AC motor-elastic linkage mechanism system is considered. Taking the drive motor and the linkage mechanism as an integrated system, the coupling dynamic equations of the system are established by the finite element method. The multiple resonance and its stability of the system are studied using the method of multiple scales. The first order approximate solutions of the multiple resonance of the system are obtained. An algorithm for determining the stability of resonance is derived. The studies show that the multiple resonance and its stability of the system are not only related to the structure parameters of the linkage mechanism, but also to the electromagnetism parameters of the motor. At last, an experiment is given to verify the results of the theoretical analysis.

  6. Effect Mechanism of Penstock on Stability and Regulation Quality of Turbine Regulating System

    Directory of Open Access Journals (Sweden)

    Wencheng Guo

    2014-01-01

    Full Text Available This paper studies the effect mechanism of water inertia and head loss of penstock on stability and regulation quality of turbine regulating system with surge tank or not and proposes the construction method of equivalent model of regulating system. Firstly, the complete linear mathematical model of regulating system is established. Then, the free oscillation equation and time response of the frequency that describe stability and regulation quality, respectively, are obtained. Finally, the effects of penstock are analysed by using stability region and response curves. The results indicate that the stability and regulation quality of system without surge tank are determined by time response of frequency which only depends on water hammer wave in penstock, while, for system with surge tank, the time response of frequency depending on water hammer wave in penstock and water-level fluctuation in surge tank jointly determines the stability and regulation quality. Water inertia of penstock mainly affects the stability and time response of frequency of system without surge tank as well as the stability and head wave of time response of frequency with surge tank. Head loss of penstock mainly affects the stability and tail wave of time response of frequency with surge tank.

  7. Controls of interactions between iron hydroxide colloid and water on REE fractionations in surface waters: Experimen-tal study on pH-controlling mechanism

    Institute of Scientific and Technical Information of China (English)

    刘丛强; 吴佳红; 于文辉

    2002-01-01

    The influence of pH on the partitioning behavior of REE at the water/particulate interface has been studied experimentally. At the beginning of colloid formation the adsorption of REE on iron hydroxide colloids is dominant, followed by REE desorption. Finally adsorption and desorption tend to reach equilibration. The capability of iron hydroxide colloids to adsorb the HREE is greater than that to adsorb the LREE. With increasing pH, LREE/HREE fractionations will take place between iron hydroxide colloids and water, leading to the reduction of their partition coefficient ratio (DLREE/DHREE). The DREE distribution patterns show Y anomalies (DY/DHo <1), with obvious REE tetrad effects appearing under low pH conditions. Experimental results have shown that there do exist REE tetrad effects in nature. In addition to pH, the chemical type of surface water and ion intensity are also the important factors controlling REE tetrad effects and leading to fractionations between particulate-adsorbed REE and dissolved REE.

  8. Improving the durability of a drag-reducing nanocoating by enhancing its mechanical stability.

    Science.gov (United States)

    Cheng, Mengjiao; Zhang, Songsong; Dong, Hongyu; Han, Shihui; Wei, Hao; Shi, Feng

    2015-02-25

    The durability of superhydrophobic surface is a major problem to restrict industrial application of superhydrophobic materials from laboratory research, which can be attributed to a more general issue of mechanical stability for superhydrophobic coatings. Therefore, in order to handle this issue, we have fabricated a mechanically stable drag-reducing coating composed of elastic polydimethylsiloxane (PDMS) and hydrophobic copper particles on model ships, which can resist mechanical abrasion and has displayed a durable drag-reducing effect. In comparison with normal Au superhydrophobic coatings, the as-prepared PDMS/copper coatings showed durable drag reduction performance with a similar drag-reducing rate before (26%) and after (24%) mechanical abrasion. The mechanism for the enhanced mechanical stability and maintained drag reduction of the superhydrophobic surfaces was investigated through characterizations of surface morphology, surface wettability, and water adhesive force evaluation before and after abrasion. This is the first demonstration to realize the application of durable drag reduction by improving the mechanical stability of superhydrophobic coatings. We do believe that superhydrophobic surfaces with good resistance to mechanical abrasion or scratching may draw wide attention and gain significant applications with durable drag-reducing properties.

  9. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements.

    Science.gov (United States)

    Zou, Yi; Jayasuriya, Sunil; Manke, Charles W; Mao, Guangzhao

    2015-09-29

    Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken

  10. Polymer adsorption and its effect on colloidal stability : a theoretical and experimental study on the polyvinyl alcohol-silver iodide system

    NARCIS (Netherlands)

    Fleer, G.J.

    1971-01-01

    The purpose of this study was to gain insight in the factors determining the stability of hydrophobic sols in the presence of polymers, with the emphasis on the destabilisation of sols by polymers and the role played by salts therein.In chapter 1. the practical importance of polymer stabilisation an

  11. Shape recognition of microbial cells by colloidal cell imprints

    Science.gov (United States)

    Borovička, Josef; Stoyanov, Simeon D.; Paunov, Vesselin N.

    2013-08-01

    We have engineered a class of colloids which can recognize the shape and size of targeted microbial cells and selectively bind to their surfaces. These imprinted colloid particles, which we called ``colloid antibodies'', were fabricated by partial fragmentation of silica shells obtained by templating the targeted microbial cells. We successfully demonstrated the shape and size recognition between such colloidal imprints and matching microbial cells. High percentage of binding events of colloidal imprints with the size matching target particles was achieved. We demonstrated selective binding of colloidal imprints to target microbial cells in a binary mixture of cells of different shapes and sizes, which also resulted in high binding selectivity. We explored the role of the electrostatic interactions between the target cells and their colloid imprints by pre-coating both of them with polyelectrolytes. Selective binding occurred predominantly in the case of opposite surface charges of the colloid cell imprint and the targeted cells. The mechanism of the recognition is based on the amplification of the surface adhesion in the case of shape and size match due to the increased contact area between the target cell and the colloidal imprint. We also tested the selective binding for colloid imprints of particles of fixed shape and varying sizes. The concept of cell recognition by colloid imprints could be used for development of colloid antibodies for shape-selective binding of microbes. Such colloid antibodies could be additionally functionalized with surface groups to enhance their binding efficiency to cells of specific shape and deliver a drug payload directly to their surface or allow them to be manipulated using external fields. They could benefit the pharmaceutical industry in developing selective antimicrobial therapies and formulations.

  12. Synthesis of nanosized silver colloids by microwave dielectric heating

    Indian Academy of Sciences (India)

    Kirti Patel; Sudhir Kapoor; D P Dave; Tulsi Mukherjee

    2005-01-01

    Silver nanosized crystallites have been synthesized in aqueous and polyols viz., ethylene glycol and glycerol, using a microwave technique. Dispersions of colloidal silver have been prepared by the reduction of silver nitrate both in the presence and absence of stabilizer poly(vinylpyrolidone) (PVP). It was observed that PVP is capable of complexing and stabilizing Ag nanoparticles formed through the reduction of Ag+ ions in water and ethylene glycol. In the case of ethylene glycol, it has been shown that the use of PVP leads to particles with a high degree of stability. The colloids are stable in glycerol for months even in the absence of stabilizer.

  13. Role of organic matter on aggregate stability and related mechanisms through organic amendments

    Science.gov (United States)

    Zaher, Hafida

    2010-05-01

    To date, only a few studies have tried to simultaneously compare the role of neutral and uronic sugars and lipids on soil structural stability. Moreover, evidence for the mechanisms involved has often been established following wetting of moist aggregates after various pre-treatments thus altering aggregate structure and resulting in manipulations on altered aggregates on which the rapid wetting process may not be involved anymore. To the best of our knowledge, the objective of this work was to study the role of neutral and uronic sugars and lipids in affecting key mechanisms (swelling rate, pressure evolution) involved in the stabilization of soil structure. A long-term incubation study (48-wk) was performed on a clay loam and a silty-clay loam amended with de-inking-secondary sludge mix at three rates (8, 16 and 24 Mg dry matter ha-1), primary-secondary sludge mix at one rate (18 Mg oven-dry ha-1) and composted de-inking sludge at one rate (24 Mg ha-1). Different structural stability indices (stability of moist and dry aggregates, the amount of dispersible clay and loss of soil material following sudden wetting) were measured on a regular basis during the incubation, along with CO2 evolved, neutral and uronic sugar, and lipid contents. During the course of the incubations, significant increases in all stability indices were measured for both soil types. In general, the improvements in stability were proportional to the amount of C added as organic amendments. These improvements were linked to a very intense phase of C mineralization and associated with increases in neutral and uronic sugars as well as lipid contents. The statistical relationships found between the different carbonaceous fractions and stability indices were all highly significant and indicated no clear superiority of one fraction over another. Paper sludge amendments also resulted in significant decreases in maximum internal pressure of aggregate and aggregate swelling following immersion in water

  14. Implementation of a capsular bag model to enable sufficient lens stabilization within a mechanical eye model

    Science.gov (United States)

    Bayer, Natascha; Rank, Elisabet; Traxler, Lukas; Beckert, Erik; Drauschke, Andreas

    2015-03-01

    Cataract still remains the leading cause of blindness affecting 20 million people worldwide. To restore the patients vision the natural lens is removed and replaced by an intraocular lens (IOL). In modern cataract surgery the posterior capsular bag is maintained to prevent inflammation and to enable stabilization of the implant. Refractive changes following cataract surgery are attributable to lens misalignments occurring due to postoperative shifts and tilts of the artificial lens. Mechanical eye models allow a preoperative investigation of the impact of such misalignments and are crucial to improve the quality of the patients' sense of sight. Furthermore, the success of sophisticated IOLs that correct high order aberrations is depending on a critical evaluation of the lens position. A new type of an IOL holder is designed and implemented into a preexisting mechanical eye model. A physiological representation of the capsular bag is realized with an integrated film element to guarantee lens stabilization and centering. The positioning sensitivity of the IOL is evaluated by performing shifts and tilts in reference to the optical axis. The modulation transfer function is used to measure the optical quality at each position. Lens stability tests within the holder itself are performed by determining the modulation transfer function before and after measurement sequence. Mechanical stability and reproducible measurement results are guaranteed with the novel capsular bag model that allows a precise interpretation of postoperative lens misalignments. The integrated film element offers additional stabilization during measurement routine without damaging the haptics or deteriorating the optical performance.

  15. Saturated Zone Colloid Transport

    Energy Technology Data Exchange (ETDEWEB)

    H. S. Viswanathan

    2004-10-07

    This scientific analysis provides retardation factors for colloids transporting in the saturated zone (SZ) and the unsaturated zone (UZ). These retardation factors represent the reversible chemical and physical filtration of colloids in the SZ. The value of the colloid retardation factor, R{sub col} is dependent on several factors, such as colloid size, colloid type, and geochemical conditions (e.g., pH, Eh, and ionic strength). These factors are folded into the distributions of R{sub col} that have been developed from field and experimental data collected under varying geochemical conditions with different colloid types and sizes. Attachment rate constants, k{sub att}, and detachment rate constants, k{sub det}, of colloids to the fracture surface have been measured for the fractured volcanics, and separate R{sub col} uncertainty distributions have been developed for attachment and detachment to clastic material and mineral grains in the alluvium. Radionuclides such as plutonium and americium sorb mostly (90 to 99 percent) irreversibly to colloids (BSC 2004 [DIRS 170025], Section 6.3.3.2). The colloid retardation factors developed in this analysis are needed to simulate the transport of radionuclides that are irreversibly sorbed onto colloids; this transport is discussed in the model report ''Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]). Although it is not exclusive to any particular radionuclide release scenario, this scientific analysis especially addresses those scenarios pertaining to evidence from waste-degradation experiments, which indicate that plutonium and americium may be irreversibly attached to colloids for the time scales of interest. A section of this report will also discuss the validity of using microspheres as analogs to colloids in some of the lab and field experiments used to obtain the colloid retardation factors. In addition, a small fraction of colloids travels with the groundwater without any significant

  16. ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

    Energy Technology Data Exchange (ETDEWEB)

    Biener, M M; Biener, J; Wichmann, A; Wittstock, A; Baumann, T F; Baeumer, M; Hamza, A V

    2011-03-24

    Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

  17. Nonlinear analysis on purely mechanical stabilization of a wheeled inverted pendulum on a slope

    CERN Document Server

    Yoshida, Katsutoshi; Hosomi, Kenta

    2015-01-01

    This paper investigates the potential for stabilizing an inverted pendulum without electric devices, using gravitational potential energy. We propose a wheeled mechanism on a slope, specifically, a wheeled double pendulum, whose second pendulum transforms gravity force into braking force that acts on the wheel. In this paper, we derive steady-state equations of this system and conduct nonlinear analysis to obtain parameter conditions under which the standing position of the first pendulum becomes asymptotically stable. In this asymptotically stable condition, the proposed mechanism descends the slope in a stable standing position, while dissipating gravitational potential energy via the brake mechanism. By numerically continuing the stability limits in the parameter space, we find that the stable parameter region is simply connected. This implies that the proposed mechanism can be robust against errors in parameter setting.

  18. Cystine Plug and Other Novel Mechanisms of Large Mechanical Stability in Dimeric Proteins

    Science.gov (United States)

    Sikora, Mateusz; Cieplak, Marek

    2012-11-01

    We identify three dimeric proteins whose mechanostability is anisotropic and should exceed 1 nN along some directions. They come with distinct mechanical clamps: either shear-based, or involving a cystine slipknot, or due to dragging of a cystine plug through a cystine ring. The latter two mechanisms are topological in nature; the cystine plug mechanism has not yet been discussed but it turns out to provide the largest resistance to stretching. Its possible applications in elastomers are discussed.

  19. Electrosteric stabilization of colloidal TiO2 nanoparticles with DNA and polyethylene glycol for selective enhancement of UV detection sensitivity in capillary electrophoresis analysis.

    Science.gov (United States)

    Alsudir, Samar; Lai, Edward P C

    2017-03-01

    A new approach to selectively enhance the ultraviolet (UV) detection sensitivity of titania (TiO2), albeit in the presence of silica (SiO2), alumina (Al2O3), and zinc oxide (ZnO), nanoparticles in capillary electrophoresis (CE) analysis was developed. Interactions of Triton X-100 (TX-100), polyethylene glycol (PEG), and deoxyribonucleic acid (DNA) with TiO2 nanoparticles produced larger CE-UV peaks at various enhancement factors. Single-stranded DNA (ssDNA) was a more effective adsorbate than double-stranded DNA (dsDNA) due to its flexible molecular structure that participated in a stronger interaction with TiO2 nanoparticles via its sugar-phosphate backbone. Disaggregation of TiO2 nanoparticles upon DNA binding due to electrosteric stabilization was validated using dynamic light scattering. PEG coating of TiO2-DNA nanoparticles further enhanced the UV detection sensitivity in CE analysis by providing extra electrosteric stabilization. This analytical technique, which involves binding of TiO2 nanoparticles with DNA followed by coating with PEG, has allowed us to achieve progressively an enhancement factor up to 13.0 ± 3.0 - fold in analytical sensitivity for the accurate determination of disaggregated TiO2 nanoparticles. Graphical Abstract Selective enhancement of UV detection sensitivity for TiO2 nanoparticles via electrosteric stabilization using ssDNA and PEG.

  20. High colloidal stability of gold nanorods coated with a peptide-ethylene glycol: Analysis by cyanide-mediated etching and nanoparticle tracking analysis.

    Science.gov (United States)

    Free, Paul; Conger, Gao; Siji, Wu; Zhang, Jing Bo; Fernig, David G

    2016-10-01

    The stability of gold nanorods was assessed following coating with various charged or uncharged ligands, mostly peptides. Highly stable monodispersed gold nanorods were obtained by coating CTAB-stabilized gold nanorods with a pentapeptide with C-terminal ethylene glycol units (peptide-EG). UV-vis spectroscopy of these nanorods suspended in saline solutions indicated no signs of aggregation, and they were easily purified using size-exclusion chromatography. A more stringent measure of nanorod stability involved observing changes in the UV-vis absorbance of gold nanorods subjected to etching with cyanide. The λmax absorbance of peptide-EG coated nanorods red-shifted in etchant solution. The hypothesis that changes in the nanorod aspect ratio led to this red-shift was confirmed by TEM analysis, which showed pit formation along the transverse axis. The etching process was followed in solution using nanoparticle tracking analysis. The red-shift was shown to occur while the particles remained mono-dispersed, and so was not due to aggregation. Adding both etchant solution and peptide-EG to the nanorods was further shown to allow modulation of the Δλmax red-shift and increase the etchant resistance of peptide-EG nanorods. Thus, very stable gold nanorods can be produced using the peptide-EG coating approach and their optical properties modulated with etchant.

  1. Realistic calculation of the low- and high-density liquid phase separation in a charged colloidal dispersion

    Science.gov (United States)

    Lai, S. K.; Peng, W. P.; Wang, G. F.

    2001-04-01

    A realistic statistical-mechanics model is applied to describe the repulsive interaction between charged colloids. The latter, in combination with the long-range van der Waals attraction simulated under excess salt environment, gives rise to a total intercolloidal particle potential showing a clear second potential minimum. Differing from the usual Derjaguin-Landau-Verwey-Overbeek (DLVO) model, the present model is valid at any finite concentration of colloids and is thus an appropriate model for investigating the low- and high-density liquid phase transition. Employing this two-body colloid-colloid potential and in conjunction with the Weeks-Chandler-Andersen [J. D. Weeks, D. Chandler, and H. C. Andersen, J. Chem. Phys. 54, 5237 (1971)] thermodynamic perturbation theory, we derive analytical expressions for the pressure, chemical potential, and related thermodynamic functions. These thermodynamic quantities were used to calculate the phase diagrams of charged colloidal dispersions in terms of the critical parameters: temperature, volume fraction, and electrolyte concentration parameter kD. Compared with the DLVO model, we find the areas enclosed within the spinodal decomposition and also the liquid-liquid coexistence curves broader in the present model for an excess salt condition κ=kDσ0300, the disparities between the two models reduce. The same thermodynamic perturbation theory has been employed to study also the weak reversible coagulation whose physical origin is attributed to the presence of the second potential minimum. We examine various colloidal parameters that affect the structure of the latter and deduce from our analysis the conditions of colloidal stability. In comparison with the measured flocculation data for a binary mixture of polystyrene lattices and water, we find that our calculated results are generally reasonable, thus lending great credence to the presently used model.

  2. Implant materials modified by colloids

    Directory of Open Access Journals (Sweden)

    Zboromirska-Wnukiewicz Beata

    2016-03-01

    Full Text Available Recent advances in general medicine led to the development of biomaterials. Implant material should be characterized by a high biocompatibility to the tissue and appropriate functionality, i.e. to have high mechanical and electrical strength and be stable in an electrolyte environment – these are the most important properties of bioceramic materials. Considerations of biomaterials design embrace also electrical properties occurring on the implant-body fluid interface and consequently the electrokinetic potential, which can be altered by modifying the surface of the implant. In this work, the surface of the implants was modified to decrease the risk of infection by using metal colloids. Nanocolloids were obtained using different chemical and electrical methods. It was found that the colloids obtained by physical and electrical methods are more stable than colloids obtained by chemical route. In this work the surface of modified corundum implants was investigated. The implant modified by nanosilver, obtained by electrical method was selected. The in vivo research on animals was carried out. Clinical observations showed that the implants with modified surface could be applied to wounds caused by atherosclerotic skeleton, for curing the chronic and bacterial inflammations as well as for skeletal reconstruction surgery.

  3. Colloids in Biotechnology

    CERN Document Server

    Fanun, Monzer

    2010-01-01

    Colloids have come a long way from when Thomas Graham coined the term colloid to describe 'pseudo solutions'. This book enables scientists to close the gap between extensive research and translation into commercial options in biomedicine and biotechnology. It covers biosurfactants and surface properties, phase behavior, and orientational change of surfactant mixtures with peptides at the interface. It also covers adsorption of polymers and biopolymers on the surface and interface, discusses colloidal nanoparticles and their use in biotechnology, and delves into bioadhesion and microencapsulati

  4. Speed Observation and Position Feedback Stabilization of Partially Linearizable Mechanical Systems

    NARCIS (Netherlands)

    Venkatraman, Aneesh; Ortega, Romeo; Sarras, Ioannis; Schaft, Arjan van der

    2010-01-01

    The problems of speed observation and position feedback stabilization of mechanical systems are addressed in this paper. Our interest is centered on systems that can be rendered linear in the velocities via a (partial) change of coordinates. It is shown that the class is fully characterized by the s

  5. Defect structure and mechanical stability of microcrystalline titanium produced by equal channel angular pressing

    Science.gov (United States)

    Betekhtin, V. I.; Kadomtsev, A. G.; Narykova, M. V.; Amosova, O. V.; Sklenicka, V.

    2017-01-01

    It is established that increases in nanoporosity and the proportion of high-angle grain boundaries in the process of equal-channel angular pressing are the main structural factors leading to reduction in mechanical stability (durability) of microcrystalline titanium during long-term tests under creeping conditions.

  6. Rheological properties and mechanical stability of new gel-entrapment systems applied in bioreactors

    NARCIS (Netherlands)

    Vogelsang, C.; Wijffels, R.H.; Ostgaard, K.

    2000-01-01

    The mechanical stability of gels applied for entrapment and retention of biocatalysts in bioreactors is of crucial importance for successful scale-up applications. Gel abrasion in agitated reactors will depend on liquid shear, bubble shear, and wall shear, as well as collisions between the gel parti

  7. A multiscale view of therapeutic protein aggregation: a colloid science perspective.

    Science.gov (United States)

    Nicoud, Lucrèce; Owczarz, Marta; Arosio, Paolo; Morbidelli, Massimo

    2015-03-01

    The formation of aggregates in protein-based pharmaceuticals is a major issue that can compromise drug safety and drug efficacy. With a view to improving protein stability, considerable effort is put forth to unravel the fundamental mechanisms underlying the aggregation process. However, therapeutic protein aggregation is a complex multistep phenomenon that involves time and length scales spanning several orders of magnitude, and strategies addressing protein aggregation inhibition are currently still largely empirical in practice. Here, we review how key concepts developed in the frame of colloid science can be applied to gain knowledge on the kinetics and thermodynamics of therapeutic protein aggregation across different length scales. In particular, we discuss the use of coarse-grained molecular interaction potentials to quantify protein colloidal stability. We then show how population balance equations simulations can provide insights into the mechanisms of aggregate formation at the mesoscale, and we highlight the strength of the concept of fractal scaling to quantify irregular aggregate morphologies. Finally, we correlate the macroscopic rheological properties of protein solutions with the occupied volume fraction and the aggregate structure. Overall, this work illustrates the power and limitations of colloidal approaches in the multiscale description of the aggregation of therapeutic proteins.

  8. Differential Effects of Hydrophobic Core Packing Residues for Thermodynamic and Mechanical Stability of a Hyperthermophilic Protein.

    Science.gov (United States)

    Tych, Katarzyna M; Batchelor, Matthew; Hoffmann, Toni; Wilson, Michael C; Hughes, Megan L; Paci, Emanuele; Brockwell, David J; Dougan, Lorna

    2016-07-26

    Proteins from organisms that have adapted to environmental extremes provide attractive systems to explore and determine the origins of protein stability. Improved hydrophobic core packing and decreased loop-length flexibility can increase the thermodynamic stability of proteins from hyperthermophilic organisms. However, their impact on protein mechanical stability is not known. Here, we use protein engineering, biophysical characterization, single-molecule force spectroscopy (SMFS), and molecular dynamics (MD) simulations to measure the effect of altering hydrophobic core packing on the stability of the cold shock protein TmCSP from the hyperthermophilic bacterium Thermotoga maritima. We make two variants of TmCSP in which a mutation is made to reduce the size of aliphatic groups from buried hydrophobic side chains. In the first, a mutation is introduced in a long loop (TmCSP L40A); in the other, the mutation is introduced on the C-terminal β-strand (TmCSP V62A). We use MD simulations to confirm that the mutant TmCSP L40A shows the most significant increase in loop flexibility, and mutant TmCSP V62A shows greater disruption to the core packing. We measure the thermodynamic stability (ΔGD-N) of the mutated proteins and show that there is a more significant reduction for TmCSP L40A (ΔΔG = 63%) than TmCSP V62A (ΔΔG = 47%), as might be expected on the basis of the relative reduction in the size of the side chain. By contrast, SMFS measures the mechanical stability (ΔG*) and shows a greater reduction for TmCSP V62A (ΔΔG* = 8.4%) than TmCSP L40A (ΔΔG* = 2.5%). While the impact on the mechanical stability is subtle, the results demonstrate the power of tuning noncovalent interactions to modulate both the thermodynamic and mechanical stability of a protein. Such understanding and control provide the opportunity to design proteins with optimized thermodynamic and mechanical properties.

  9. Immobilization of mercury by carboxymethyl cellulose stabilized iron sulfide nanoparticles: reaction mechanisms and effects of stabilizer and water chemistry.

    Science.gov (United States)

    Gong, Yanyan; Liu, Yuanyuan; Xiong, Zhong; Zhao, Dongye

    2014-04-01

    Iron sulfide (FeS) nanoparticles were prepared with sodium carboxymethyl cellulose (CMC) as a stabilizer, and tested for enhanced removal of aqueous mercury (Hg(2+)). CMC at ≥0.03 wt % fully stabilized 0.5 g/L of FeS (i.e., CMC-to-FeS molar ratio ≥0.0006). FTIR spectra suggested that CMC molecules were attached to the nanoparticles through bidentate bridging and hydrogen bonding. Increasing the CMC-to-FeS molar ratio from 0 to 0.0006 enhanced mercury sorption capacity by 20%; yet, increasing the ratio from 0.0010 to 0.0025 diminished the sorption by 14%. FTIR and XRD analyses suggested that precipitation (formation of cinnabar and metacinnabar), ion exchange (formation of Hg0.89Fe0.11S), and surface complexation were important mechanisms for mercury removal. A pseudo-second-order kinetic model was able to interpret the sorption kinetics, whereas a dual-mode isotherm model was proposed to simulate the isotherms, which considers precipitation and adsorption. High mercury uptake was observed over the pH range of 6.5-10.5, whereas significant capacity loss was observed at pH 106 mg/L) and organic matter (5 mg/L as TOC) modestly inhibited mercury uptake. The immobilized mercury remained stable when preserved for 2.5 years at pH above neutral.

  10. Liquid crystal colloids

    CERN Document Server

    Muševič, Igor

    2017-01-01

    This book brings together the many concepts and discoveries in liquid crystal colloids contributed over the last twenty years and scattered across numerous articles and book chapters. It provides both a historical overview of the development of the field and a clear perspective on the future applications in photonics. The book covers all phenomena observed in liquid crystal colloids with an emphasis on experimental tools and applications of topology in condensed matter, as well as practical micro-photonics applications. It includes a number of spectacular manifestations of new topological phenomena not found or difficult to observe in other systems. Starting from the early works on nematic colloids, it explains the basics of topological defects in ordered media, charge and winding, and the elastic forces between colloidal particles in nematics. Following a detailed description of experimental methods, such as optical tweezing and particle tracking, the book eases the reader into the theoretical part, which de...

  11. Confocal microscopy of colloids

    Energy Technology Data Exchange (ETDEWEB)

    Prasad, V; Semwogerere, D; Weeks, Eric R [Department of Physics, Emory University, Atlanta, GA 30322 (United States)

    2007-03-21

    Colloids have increasingly been used to characterize or mimic many aspects of atomic and molecular systems. With confocal microscopy these colloidal particles can be tracked spatially in three dimensions with great precision over large time scales. This review discusses equilibrium phases such as crystals and liquids, and non-equilibrium phases such as glasses and gels. The phases that form depend strongly on the type of particle interaction that dominates. Hard-sphere-like colloids are the simplest, and interactions such as the attractive depletion force and electrostatic repulsion result in more non-trivial phases which can better model molecular materials. Furthermore, shearing or otherwise externally forcing these colloids while under microscopic observation helps connect the microscopic particle dynamics to the macroscopic flow behaviour. Finally, directions of future research in this field are discussed. (topical review)

  12. Contracts, Vouchers, and Child Care Subsidy Stability: A Preliminary Look at Associations between Subsidy Payment Mechanism and Stability of Subsidy Receipt

    Science.gov (United States)

    Holod, Aleksandra; Johnson, Anna D.; Martin, Anne; Gardner, Margo; Brooks-Gunn, Jeanne

    2012-01-01

    Background: The federal child care subsidy program, funded through the Child Care and Development Fund (CCDF), is the nation's largest public investment in early child care. However, little is known about whether and how subsidy payment mechanisms relate to the stability of subsidy receipt or the stability of children's care arrangements.…

  13. Mechanical and Thermophysical Properties of Cement and/or Paper (Cellulose Stabilized Compressed Clay Bricks

    Directory of Open Access Journals (Sweden)

    Emmanuel OUEDRAOGO

    2015-05-01

    Full Text Available This article presents an experimental study of the characterization of clay blocks stabilized with cement and/or recycled papers as construction materials. When they are utilized as finish for building envelops, they must have appropriate mechanical strength and water stability. The measurements of the mechanical and thermophysical properties show differences between the properties of four investigated specimens. Mechanical properties such as compression and tensile tresses of clay-cement and clay-cement-paper mixtures are found to be quite similar but are two to three times greater respectively for clay-paper and purely clay blocks. The values of the thermophysical properties of blocks incorporating paper show improvement of their thermo insulation performances.

  14. Structural, Mechanical Properties and Thermal Stability of ZrAlN Coatings

    Institute of Scientific and Technical Information of China (English)

    WANG M X; ZHANG J J; LID J

    2004-01-01

    Dry machining will result in elevated temperatures at the tool surface ( 800 ~ 1000 ℃ ). So, coating materials that can provide protection for cutting tools at these temperatures are of great technological interests. ZrAlN coating is proposed to possess high-temperature stable structural and mechanical properties due to the addition of the alloying element.ZrAlN coatings were grown using a dc reactive magnetron sputtering. The XRD and ultramicro-indentor were employed to investigate the effects of reaction gas partial pressure and substrate bias on structural, mechanical properties, as well as hightemperature stability. The ZrAlN coating, when deposited under optimum conditions ( -37 V substrate bias and 1.5 10-7 Torr N2 partial pressure), showed smooth surface with 22 GPa hardness and 2.2 GPa internal stress. Its structural and mechanical properties kept high-temperature stability before and after annealing .

  15. Aggregation kinetics of coalescing polymer colloids.

    Science.gov (United States)

    Gauer, Cornelius; Jia, Zichen; Wu, Hua; Morbidelli, Massimo

    2009-09-01

    The aggregation behavior of a soft, rubbery colloidal system with a relatively low glass transition temperature, T(g) approximately -20 degrees C, has been investigated. It is found that the average gyration and hydrodynamic radii, R(g) and R(h), measured by light scattering techniques, evolve in time in parallel, without exhibiting the crossover typical of rigid particle aggregation. Cryogenic scanning electron microscopy (cryo-SEM) images reveal sphere-like clusters, indicating that complete coalescence between particles occurs during aggregation. Since coalescence leads to a reduction in the total colloidal surface area, the surfactant adsorption equilibrium, and thus the colloidal stability, change in the course of aggregation. It is found that to simulate the observed kinetic behavior based on the population balance equations, it is necessary to assume that all the clusters are spherical and to account for variations in the colloidal stability of each aggregating particle pair with time. This indicates that, for the given system, the coalescence is very fast, i.e., its time scale is much smaller than that of the aggregation.

  16. Microstructure and thermal stability of mechanically alloyed Al3Ti/Al alloy

    Institute of Scientific and Technical Information of China (English)

    林建国; 魏浩岩; 黄正

    2001-01-01

    The microstructure stability of Al3Ti/Al alloy prepared by mechanical alloying (MA) was investigated in the simulating environment in which they may be used. The results show that the MA alloy possesses fine microstructure (the grain size is about 0.5  μm). After cycling loaded followed by heat exposure at 350  ℃ for 24  h, no microstructure coarsening of the alloy occurred, which means that the Al3Ti/Al alloy behaves good microstructure stability at high temperature. The compression yield strength of the alloy reaches up to 247  MPa at 350  ℃.

  17. Influence of biofilms on colloid transport: investigations with laponite as a model colloid

    Energy Technology Data Exchange (ETDEWEB)

    Leon-Morales, C.F.; Flemming, H.C.; Leis, A. [Duisburg Univ. (Germany). Inst. for Interface Biotechnology

    2003-07-01

    The synthetic clay mineral laponite RD was used as a model compound to investigate colloid transport in the presence of bacterial biofilms. A complex but pronounced delay in the transport of laponite was observed in colonised porous media, clearly demonstrating the influence of attached bacterial biomass on colloid transport. The transport of laponite under conditions which promoted laponite aggregation was associated with release of attached bacteria; this effect was shown to be independent of ionic strength, indicating that the colloids caused detachment of bacteria. Two major mechanisms are proposed to account for the different colloid transport patterns obtained in the presence or absence of biomass: (1) hydrodynamic effects due to aggregation of laponite and subsequent blockage of a proportion of the flow channels, and (2) sorption of laponite by bacterial biomass. (orig.)

  18. Dynamics of Fractal Cluster Gels with Embedded Active Colloids

    Science.gov (United States)

    Szakasits, Megan E.; Zhang, Wenxuan; Solomon, Michael J.

    2017-08-01

    We find that embedded active colloids increase the ensemble-averaged mean squared displacement of particles in otherwise passively fluctuating fractal cluster gels. The enhancement in dynamics occurs by a mechanism in which the active colloids contribute to the average dynamics both directly through their own active motion and indirectly through their excitation of neighboring passive colloids in the fractal network. Fractal cluster gels are synthesized by addition of magnesium chloride to an initially stable suspension of 1.0 μ m polystyrene colloids in which a dilute concentration of platinum coated Janus colloids has been dispersed. The Janus colloids are thereby incorporated into the fractal network. We measure the ensemble-averaged mean squared displacement of all colloids in the gel before and after the addition of hydrogen peroxide, a fuel that drives diffusiophoretic motion of the Janus particles. The gel mean squared displacement increases by up to a factor of 3 for an active to passive particle ratio of 1 ∶20 and inputted active energy—defined based on the hydrogen peroxide's effect on colloid swim speed and run length—that is up to 9.5 times thermal energy, on a per particle basis. We model the enhancement in gel particle dynamics as the sum of a direct contribution from the displacement of the Janus particles themselves and an indirect contribution from the strain field that the active colloids induce in the surrounding passive particles.

  19. Sublethal concentrations of silver nanoparticles affect the mechanical stability of biofilms.

    Science.gov (United States)

    Grün, Alexandra Y; Meier, Jutta; Metreveli, George; Schaumann, Gabriele E; Manz, Werner

    2016-12-01

    Bacterial biofilms are most likely confronted with silver nanoparticles (Ag NPs) as a pollutant stressor in aquatic systems. In this study, biofilms of Aquabacterium citratiphilum were exposed for 20 h to 30 and 70 nm citrate stabilized Ag NPs in low-dose concentrations ranging from 600 to 2400 μg l(-1), and the Ag NP-mediated effects on descriptive, structural, and functional biofilm characteristics, including viability, protein content, architecture, and mechanical stability, were investigated. Viability, based on the bacterial cell membrane integrity of A. citratiphilum, as determined by epifluorescence microscopy, remained unaffected after Ag NP exposure. Moreover, in contrast to information in the current literature, protein contents of cells and extracellular polymeric substances (EPS) and biofilm architecture, including dry mass, thickness, and density, were not significantly impacted by exposure to Ag NPs. However, the biofilms themselves served as effective sinks for Ag NPs, exhibiting enrichment factors from 5 to 8. Biofilms showed a greater capacity to accumulate 30 nm sized Ag NPs than 70 nm Ag NPs. Furthermore, Ag NPs significantly threatened the mechanical stability of biofilms, as determined by a newly developed assay. For 30 nm Ag NPs, the mechanical stability of biofilms decreased as the Ag NP concentrations applied to them increased. In contrast, 70 nm Ag NPs produced a similar decrease in mechanical stability for each applied concentration. Overall, this finding demonstrates that exposure to Ag NPs triggers remarkable changes in biofilm adhesion and/or cohesiveness. Because of biofilm-mediated ecological services, this response raises environmental concerns regarding Ag NP release into freshwater systems, even in sublethal concentrations.

  20. Engineering Proteins with Enhanced Mechanical Stability by Force Specific Sequence Motifs

    Science.gov (United States)

    Lu, Wenzhe; Negi, Surendra; Oberhauser, Andres F.; Braun, Werner

    2012-01-01

    Use of atomic force microscopy (AFM) has recently led to a better understanding of the molecular mechanisms of the unfolding process by mechanical forces; however, the rational design of novel proteins with specific mechanical strength remains challenging. We have approached this problem from a new perspective that generates linear physical-chemical properties (PCP) motifs from a limited AFM data set. Guided by our linear sequence analysis we designed and analyzed four new mutants of the titin I1 domain with the goal of increasing the domain's mechanical strength. All four mutants could be cloned and expressed as soluble proteins. AFM data indicate that at least two of the mutants have increased molecular mechanical strength. This observation suggests that the PCP method is useful to graft sequences specific for high mechanical stability to weak proteins to increase their mechanical stability, and represents an additional tool in the design of novel proteins besides steered molecular dynamics calculations, coarse grained simulations and phi-value analysis of the transition state. PMID:22274941

  1. Equilibrium crystal phases of triblock Janus colloids

    Science.gov (United States)

    Reinhart, Wesley F.; Panagiotopoulos, Athanassios Z.

    2016-09-01

    Triblock Janus colloids, which are colloidal spheres decorated with attractive patches at each pole, have recently generated significant interest as potential building blocks for functional materials. Their inherent anisotropy is known to induce self-assembly into open structures at moderate temperatures and pressures, where they are stabilized over close-packed crystals by entropic effects. We present a numerical investigation of the equilibrium phases of triblock Janus particles with many different patch geometries in three dimensions, using Monte Carlo simulations combined with free energy calculations. In all cases, we find that the free energy difference between crystal polymorphs is less than 0.2 kBT per particle. By varying the patch fraction and interaction range, we show that large patches stabilize the formation of structures with four bonds per patch over those with three. This transition occurs abruptly above a patch fraction of 0.30 and has a strong dependence on the interaction range. Furthermore, we find that a short interaction range favors four bonds per patch, with longer range increasingly stabilizing structures with only three bonds per patch. By quantifying the effect of patch geometry on the stability of the equilibrium crystal structures, we provide insights into the fundamental design rules for constructing complex colloidal crystals.

  2. On the mechanical stability of uranyl peroxide hydrates: Implications for nuclear fuel degradation

    Energy Technology Data Exchange (ETDEWEB)

    Weck, Philippe F.; Kim, Eunja; Buck, Edgar C.

    2015-09-11

    The mechanical properties and stability of studtite, (UO2)(O2)(H2O)2·2H2O, and metastudtite, (UO2)(O2)(H2O)2, two important corrosion phases observed on spent nuclear fuel exposed to water, have been investigated using density functional perturbation theory. While (UO2)(O2)(H2O)2 satisfies the necessary and sufficient Born criteria for mechanical stability, (UO2)(O2)(H2O)2·2H2O is found to be mechanically metastable, which might be the underlying cause of the irreversibility of the studtite to metastudtite transformation. According to Pugh’s and Poisson’s ratios and the Cauchy pressure, both phases are considered ductile and shear modulus is the parameter limiting their mechanical stability. Debye temperatures of 294 and 271 K are predicted for polycrystalline (UO2)(O2)(H2O)2·2H2O and (UO2)(O2)(H2O)2, suggesting a lower micro-hardness of metastudtite.

  3. A stability-based mechanism for hysteresis in the walk-trot transition in quadruped locomotion.

    Science.gov (United States)

    Aoi, Shinya; Katayama, Daiki; Fujiki, Soichiro; Tomita, Nozomi; Funato, Tetsuro; Yamashita, Tsuyoshi; Senda, Kei; Tsuchiya, Kazuo

    2013-04-01

    Quadrupeds vary their gaits in accordance with their locomotion speed. Such gait transitions exhibit hysteresis. However, the underlying mechanism for this hysteresis remains largely unclear. It has been suggested that gaits correspond to attractors in their dynamics and that gait transitions are non-equilibrium phase transitions that are accompanied by a loss in stability. In the present study, we used a robotic platform to investigate the dynamic stability of gaits and to clarify the hysteresis mechanism in the walk-trot transition of quadrupeds. Specifically, we used a quadruped robot as the body mechanical model and an oscillator network for the nervous system model to emulate dynamic locomotion of a quadruped. Experiments using this robot revealed that dynamic interactions among the robot mechanical system, the oscillator network, and the environment generate walk and trot gaits depending on the locomotion speed. In addition, a walk-trot transition that exhibited hysteresis was observed when the locomotion speed was changed. We evaluated the gait changes of the robot by measuring the locomotion of dogs. Furthermore, we investigated the stability structure during the gait transition of the robot by constructing a potential function from the return map of the relative phase of the legs and clarified the physical characteristics inherent to the gait transition in terms of the dynamics.

  4. Deciphering Molecular Mechanisms of Interface Buildup and Stability in Porous Si/Eumelanin Hybrids

    Directory of Open Access Journals (Sweden)

    Elisa Pinna

    2017-07-01

    Full Text Available Porous Si/eumelanin hybrids are a novel class of organic–inorganic hybrid materials that hold considerable promise for photovoltaic applications. Current progress toward device setup is, however, hindered by photocurrent stability issues, which require a detailed understanding of the mechanisms underlying the buildup and consolidation of the eumelanin–silicon interface. Herein we report an integrated experimental and computational study aimed at probing interface stability via surface modification and eumelanin manipulation, and at modeling the organic–inorganic interface via formation of a 5,6-dihydroxyindole (DHI tetramer and its adhesion to silicon. The results indicated that mild silicon oxidation increases photocurrent stability via enhancement of the DHI–surface interaction, and that higher oxidation states in DHI oligomers create more favorable conditions for the efficient adhesion of growing eumelanin.

  5. Structural and Mechanical Characterization of Sustainable Composites Based on Recycled and Stabilized Fly Ash

    Directory of Open Access Journals (Sweden)

    Stefano Besco

    2014-08-01

    Full Text Available This paper reports the results on the use of an innovative inert, based on stabilized fly ash from municipal solid waste incineration as a filler for polypropylene. The starting material, which contains large quantities of leachable Pb and Zn, was stabilized by means of an innovative process using rice husk ash as a waste silica source, together with other fly ashes, such as coal fly ash and flue gas desulfurization residues. The use of all waste materials to obtain a new filler makes the proposed technology extremely sustainable and competitive. The new composites, obtained by using the stabilized material as a filler for polypropylene, were characterized and their mechanical properties were also investigated. A comparison with a traditional polypropylene and calcium carbonate based compound was also done. This research activity was realized in the frame of the COSMOS-RICE project, financed by the EU Commission.

  6. Structural evolution and stability of mechanically alloyed Fe-Ni nanocrystalline

    Institute of Scientific and Technical Information of China (English)

    CHEN Zi; LIU Qi-zheng; MENG Qing-ping; RONG Yong-hua

    2005-01-01

    The structural evolution and stability of Fe100-xNix(x=10, 20, 35, 50) alloys prepared by mechanical alloying were investigated through X-ray diffraction analysis and transmission electron microscopy. The intrinsic conditions of preparation determining phase stability in nanocrystalline were clarified. After being milled for 120 h, the powders of Fe90Ni10 and Fe80Ni20 consist of a single α(bcc) phase, Fe30Ni30 powders are a single γ(fcc), and for Fe65Ni35 powders there is co-existence of α and γ phases. The as-milled Fe80Ni20 powders annealed at 680 ℃ exhibits the stability of high-temperature γ phase at room temperature, which is consistent with the theoretical prediction.

  7. Study on Roll Instability Mechanism and Stability Index of Articulated Steering Vehicles

    Directory of Open Access Journals (Sweden)

    Xuefei Li

    2016-01-01

    Full Text Available This study examines the roll instability mechanism and stability index of articulated steering vehicles (ASVs by taking wheel loaders as the research object. A seven-degree-of-freedom nonlinear dynamics model of the ASVs is built on the basis of multibody dynamics. A physical prototype model of an ASV is designed and manufactured to validate the dynamic model. Test results reasonably agree with the simulation results, which indicates that the established dynamic model can reasonably describe ASV movements. Detailed analysis of the rollover stability of the wheel loader is performed with the use of the established dynamic model. Analysis results show that rollover will occur when the roll angular velocity exceeds a critical threshold, which is affected by lateral acceleration and slope angle. On this basis, a dynamic stability index applicable to the ASVs is presented.

  8. Morphological instability of a non-equilibrium ice-colloid interface

    KAUST Repository

    Peppin, S. S. L.

    2009-10-02

    We assess the morphological stability of a non-equilibrium ice-colloidal suspension interface, and apply the theory to bentonite clay. An experimentally convenient scaling is employed that takes advantage of the vanishing segregation coefficient at low freezing velocities, and when anisotropic kinetic effects are included, the interface is shown to be unstable to travelling waves. The potential for travelling-wave modes reveals a possible mechanism for the polygonal and spiral ice lenses observed in frozen clays. A weakly nonlinear analysis yields a long-wave evolution equation for the interface shape containing a new parameter related to the highly nonlinear liquidus curve in colloidal systems. We discuss the implications of these results for the frost susceptibility of soils and the fabrication of microtailored porous materials. © 2009 The Royal Society.

  9. Spherical colloidal photonic crystals.

    Science.gov (United States)

    Zhao, Yuanjin; Shang, Luoran; Cheng, Yao; Gu, Zhongze

    2014-12-16

    CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be

  10. Thermal stabilities and decomposition mechanism of amino- and hydroxyl-functionalized ionic liquids

    Energy Technology Data Exchange (ETDEWEB)

    Xue, Zhimin; Zhang, Yuwei [Department of Chemistry, Renmin University of China, Beijing 100872 (China); Zhou, Xiao-qin [College of Chemistry, Qufu Normal University, Shandong, Qufu 273165 (China); Cao, Yuanyuan [Department of Chemistry, Renmin University of China, Beijing 100872 (China); Mu, Tiancheng, E-mail: tcmu@chem.ruc.edu.cn [Department of Chemistry, Renmin University of China, Beijing 100872 (China)

    2014-02-01

    Highlights: • The long term thermal stabilities of [C{sub 2}NH{sub 2}MIM][Br] and [C{sub 3}OHMIM][Cl] are overestimated. • The thermal decomposition mechanisms of [C{sub 2}NH{sub 2}MIM][Br] and [C{sub 3}OHMIM][Cl] are complicated. • Bimolecular nucleophilic substitution (SN2) is the main reaction mechanism. - Abstract: Thermal stabilities and thermal decomposition mechanisms of amino-functionalized ionic liquid (IL) 1-aminoethyl-3-methylimidazolium bromide ([C{sub 2}NH{sub 2}MIM][Br]) and hydroxyl-functionalized IL 1-hydropropyl-3-methylimidazolium chloride ([C{sub 3}OHMIM][Cl]) were investigated by thermogravimetric analysis (TGA), TG–mass spectroscopy (TG–MS), density functional theory (DFT), and nuclear magnetic resonance (NMR) spectrum. Results show that the [C{sub 2}NH{sub 2}MIM][Br] and [C{sub 3}OHMIM][Cl] are stable up to 200 °C and 220 °C, respectively. Also, DFT calculation indicates that the thermal decomposition mechanisms of [C{sub 2}NH{sub 2}MIM][Br] and [C{sub 3}OHMIM][Cl] are complicated, while bimolecular nucleophilic substitution (SN2) is the main reaction mechanism. TG–MS and NMR spectra further prove the mechanisms.

  11. [Discussing of influence mechanism of Chinese herbal monomer on physical stability of cream].

    Science.gov (United States)

    Yin, Hui-Fu; Nie, He-Yun; Wang, Sen; Zhu, Wei-Feng; Li, Rong-Miao

    2014-10-01

    This study left flavonoids and alkaloids Chinese herbal monomer with common parent nucleus as cream base carriages drug respectively, cream base were prepared with stable span 60-tween 80 emulsification system. The near-infrared stability analysis technology was performed to quantitatively characterize the physical stability of cream. Base on the theory of gel network structure, theory of emulsification, theory of solubility parameter and theory of double layer, the influence mechanism of Chinese herbal monomer on physical stability of cream was discussed. The results showed that tetrahydropalmatine, matrine and naringenin had similar solubility parameter value with cream base material, creams prepared with those Chinese herbal monomer have higher Zeta potential value and stronger physical stability, and that those creams had similar microstructure information with cream base. However, a larger solubility parameter difference exists between baicalin, baicalein, berberine, palmatine and cream base material. Creams prepared with those Chinese herbal monomers had lower Zeta potential value and poorer physical stability, and that those creams had great different microstructure information with cream base.

  12. Dynamics of the colloidal suspensions

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hai-yan; MA Hong-ru

    2006-01-01

    This article offers a survey on our current knowledge of the dynamics of the colloidal suspension,where each particle experiences the friction force with solvent,hydrodynamic interaction,and potential force from surrounding particles and thermodynamic force.It further contains a summary of the basic concepts about microstructures and equilibrium properties,and of analytical and numerical methods,which are relevant for the theoretical description of the suspensions.The description of the dynamics of colloidal particles,based on the generalized Smoluchowski equation,is justified for the time scale accessible in DLS experiments.The combined influence of hard sphere or electrostatic potential and solvent-mediated hydrodynamic interaction on the short-time dynamics of monodisperse suspensions is investigated in detail.A thorough study of tracer-diffusion in hard sphere and charge-stabilized suspensions is presented.Mean-square displacements and long-time tracer-diffusion coefficients are calculated with two alternative approximations,i.e.,a mode-coupling scheme and a single relaxation time ansatz.

  13. Effect of TiO2 Nanoparticles on Photochromism of WO3 Colloids

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    WO3 and TiO2 colloids were synthesized by the hydrolysis technique and part of the TiO2 colloid was treated by means of the hydrothermal method. The photochromic performances of the resulting materials obtained via combining the WO3 colloid with the treated TiO2 colloid and the non-treated TiO2 colloid, respectively, are very different. The TiO2 colloid without hydrothermal treatment can effectively improve the photochromic performance of the WO3 colloid. The TiO2 nanoparticles were investigated in detail by XRD, TEM, surface photovoltage spectra(SPS) and field-induced surface photovoltage spectrometry(FISPS). The photochromism mechanism of WO3 colloid is discussed.

  14. γ-Ray irradiation stability and damage mechanism of glycidyl amine epoxy resin

    Science.gov (United States)

    Diao, Feiyu; Zhang, Yan; Liu, Yujian; Fang, Jun; Luan, Weilin

    2016-09-01

    Irradiation stability of triglycidyl-p-aminophenol (TGPAP) epoxy resins was evaluated according to the changes of physico-chemical and mechanical properties under 60Co γ-ray irradiation with a dose rate of 10 kGy/h. The result shows that with the increase of radiation dose, bending strength, thermal stability, free radical concentration and storage modulus of epoxy resin decrease first, then increase slightly, and decline sharply at the end with a dose of 960 kGy, due to competition effects between radiation-induced degradation and cross-linking reaction. The damage mechanism was derived by analyzing structure and composition change of AFG-90 resins after irradiation via IR and XPS. Irradiation will result in weak bond breaking such as Csbnd C and Csbnd N bond, and new bond forming like Cdbnd C and Cdbnd O.

  15. Trajectory Generation and Stability Analysis for Reconfigurable Klann Mechanism Based Walking Robot

    Directory of Open Access Journals (Sweden)

    Jaichandar Kulandaidaasan Sheba

    2016-06-01

    Full Text Available Reconfigurable legged robots based on one degree of freedom are highly desired because they are effective on rough and irregular terrains and they provide mobility in such terrain with simple control schemes. It is necessary that reconfigurable legged robots should maintain stability during rest and motion, with a minimum number of legs while maintaining their full range of walking patterns resulting from different gait configuration. In this paper we present a method to generate input trajectory for reconfigurable quadruped robots based on Klann mechanism to properly synchronize movement. Six useful gait cycles based on this reconfigurable Klann mechanism for quadruped robots has been clearly shown here. The platform stability for these six useful gait cycles are validated through simulated results which clearly shows the capabilities of reconfigurable design.

  16. First-principles calculations of structural stability and mechanical properties of tungsten carbide under high pressure

    Science.gov (United States)

    Li, Xinting; Zhang, Xinyu; Qin, Jiaqian; Zhang, Suhong; Ning, Jinliang; Jing, Ran; Ma, Mingzhen; Liu, Riping

    2014-11-01

    The structural stability and mechanical properties of WC in WC-, MoC- and NaCl-type structures under high pressure are investigated systematically by first-principles calculations. The calculated equilibrium lattice constants at zero pressure agree well with available experimental and theoretical results. The formation enthalpy indicates that the most stable WC is in WC-type, then MoC-type finally NaCl-type. By the elastic stability criteria, it is predicted that the three structures are all mechanically stable. The elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν of the three structures are studied in the pressure range from 0 to 100 GPa. Furthermore, by analyzing the B/G ratio, the brittle/ductile behavior under high pressure is assessed. Moreover, the elastic anisotropy of the three structures up to 100 GPa is also discussed in detail.

  17. THE EUROPEAN MECHANISM FOR FINANCIAL STABILITY AND THE EURO-PLUS PACT

    Directory of Open Access Journals (Sweden)

    AUGUSTIN FUEREA

    2012-05-01

    Full Text Available The economic crisis that has affected countries from all continents has generated, among others, also a strong financial crisis, which in turn, has caused serious imbalances in the economic and financial environment of EU Member States.Under these circumstances, the Council, being in an exceptional situation, “outside the control of Member States”, as it itself states in the Preamble to Regulation No. 407/2010, considered necessary, “the immediate establishment of a stabilization mechanism at EU level in order to maintain the financial stability in the European Union”, mechanism that “would enable the Union to respond in a coordinated, rapid and effective way to the serious difficulties undergone by a certain Member State”

  18. Thermodynamic and mechanical stabilities of tantalum nitride Ta2N3

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Chao [Los Alamos National Laboratory; Lin, Zhijun [Los Alamos National Laboratory; Zhao, Yusheng [Los Alamos National Laboratory

    2009-01-01

    We perform first-principles density functional calculations on a newly discovered tantalum nitride with an orthorhombic U{sub 2}S{sub 3} structure to assess its thermodynamic and mechanical stabilities. Our random search unveils a tetragonal Ta{sub 2}N{sub 3} structure that is energetically more favorable than an orthorhombic Ta{sub 2}N{sub 3} at zero pressure. We predict that the tetragonal Ta{sub 2}N{sub 3} transforms into the orthorhombic phase above a relatively low pressure of 7.7 GPa. Single-crystal elastic constant calculations reveal that orthorhombic Ta{sub 2}N{sub 3} is mechanically unstable because of a negative c{sub 66}. Our calculations suggest that minor oxygen substitution for nitrogen plays an important role in stabilizing the orthorhombic Ta{sub 2}N{sub 3} structure.

  19. Physical factors affecting the transport and fate of colloids in saturated porous media

    Science.gov (United States)

    Bradford, Scott A.; Yates, Scott R.; Bettahar, Mehdi; Simunek, Jirka

    2002-12-01

    Saturated soil column experiments were conducted to explore the influence of colloid size and soil grain size distribution characteristics on the transport and fate of colloid particles in saturated porous media. Stable monodispersed colloids and porous media that are negatively charged were employed in these studies. Effluent colloid concentration curves and the final spatial distribution of retained colloids by the porous media were found to be highly dependent on the colloid size and soil grain size distribution. Relative peak effluent concentrations decreased and surface mass removal by the soil increased when the colloid size increased and the soil median grain size decreased. These observations were attributed to increased straining of the colloids; i.e., blocked pores act as dead ends for the colloids. When the colloid size is small relative to the soil pore sizes, straining becomes a less significant mechanism of colloid removal and attachment becomes more important. Mathematical modeling of the colloid transport experiments using traditional colloid attachment theory was conducted to highlight differences in colloid attachment and straining behavior and to identify parameter ranges that are applicable for attachment models. Simulated colloid effluent curves using fitted first-order attachment and detachment parameters were able to describe much of the effluent concentration data. The model was, however, less adequate at describing systems which exhibited a gradual approach to the peak effluent concentration and the spatial distribution of colloids when significant mass was retained in the soil. Current colloid filtration theory did not adequately predict the fitted first-order attachment coefficients, presumably due to straining in these systems.

  20. Colloidal quantum dot light-emitting devices

    Directory of Open Access Journals (Sweden)

    Vanessa Wood

    2010-07-01

    Full Text Available Colloidal quantum dot light-emitting devices (QD-LEDs have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI. We review the key advantages of using quantum dots (QDs in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs – optical excitation, Förster energy transfer, and direct charge injection – that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt. We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs.

  1. Curing Kinetics, Mechanical Properties and Thermal Stability of Epoxy/Graphene Nanoplatelets (GNPs) Powder Coatings

    Institute of Scientific and Technical Information of China (English)

    ZHI Maoyong; HUANG Wanxia

    2016-01-01

    Epoxy/graphene nanoplatelets (GNPs) powder coatings were fabricated using ultrasonic pre-dispersion of GNPs and melt-blend extrusion method. The isothermal curing kinetics of epoxy/GNPs powder coating were monitored by means of real-time Fourier transform infrared spectroscopy (FT-IR) with a heating cell. The mechanical properties of the epoxy/GNPs cured coatings had been investigated, by evaluating their fracture surfaces with ifeld-emission scanning electron microscopy (FE-SEM) after three-point-bending tests. The thermal stability of the epoxy/GNPs cured coatings was studied by thermo-gravimetric analysis (TGA). The isothermal curing kinetics result showed that the GNPs would not affect the autocatalytic reaction mechanism, but the loading of GNPs below 1.0 wt % additive played a prompting role in the curing of the epoxy/GNPs powder coatings. The fracture strain, fracture toughness and impact resistance of the epoxy/GNPs cured coatings increased dramatically at low levels of GNPs loading (1 wt %), indicating that the GNPs could improve the toughness of the epoxy/GNPs powder coatings. Furthermore, from FE-SEM studies of the fracture surfaces, the possible toughening mechanisms of the epoxy/GNPs cured coatings were proposed. TGA result showed that the incorporation of GNPs improved the thermal stability of the cured coatings. Hence, the GNPs modiifed epoxy can be an efifcient approach to toughen epoxy powder coating along with improving their thermal stability.

  2. Chemical-mechanical stability of the hierarchical structure of shell nacre

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The hierarchical structure and mechanical property of shell nacre are experimentally investigated from the new aspects of chemical stability and chemistry-mechanics coupling. Through chemical deproteinization or demineralization methods together with characterization techniques at micro/nano scales,it is found that the nacre of abalone,haliotis discus hannai,contains a hierarchical structure stacked with irregular aragonite platelets and interplatelet organic matrix thin layers. Yet the aragonite platelet itself is a nanocomposite consisting of nanoparticles and intraplatelet organic matrix framework. The mean diameter of the nanoparticles and the distribution of framework are quite different for different platelets. Though the interplatelet and in-traplatelet organic matrix can be both decomposed by sodium hydroxide solution,the chemical stability of individual aragonite platelets is much higher than that of the microstructure stacked with them. Further,macroscopic bending test or nanoindentation experiment is performed on the micro/nanostructure of nacre after sodium hydroxide treatment. It is found that the Young’s modulus of both the stacked microstructure and nanocomposite platelet reduced. The reduction of the microstructure is more remark than that of the platelet. Therefore the chemical-mechanical stability of the nanocomposite platelet itself is much higher than that of the stacked microstructure of nacre.

  3. Initial mechanical stability of cementless highly-porous titanium tibial components

    Energy Technology Data Exchange (ETDEWEB)

    Stone, Timothy Brandon [Los Alamos National Laboratory; Amer, Luke D [Los Alamos National Laboratory; Warren, Christopher P [Los Alamos National Laboratory; Cornwell, Phillip [Los Alamos National Laboratory; Meneghini, R Michael [UNIV OF CONNECTICUT HEALTH CENTER

    2008-01-01

    Cementless fixation in total knee replacement has seen limited use since reports of early failure surfaced in the late 80s and early 90s. However the emergence of improved biomaterials, particularly porous titanium and tantalum, has led to a renewed interest in developing a cementless tibial component to enhance long-term survivorship of the implants. Cement is commonly employed to minimize micromotion in new implants but represents a weak interface between the implant and bone. The elimination of cement and application of these new biomaterials, which theoretically provide improved stability and ultimate osseointegration, would likely result in greater knee replacement success. Additionally, the removal of cement from the procedure would help minimize surgical durations and get rid of the time needed for curing, thereby the chance of infection. The purpose of this biomechanical study was twofold. The first goal was to assess whether vibration analysis techniques can be used to evaluate and characterize initial mechanical stability of cementless implants more accurately than the traditional method of micromotion determination, which employs linear variable differential transducers (LVDTs). Second, an evaluative study was performed to determine the comparative mechanical stability of five designs of cementless tibial components under mechanical loading designed to simulate in vivo forces. The test groups will include a cemented Triathlon Keeled baseplate control group, three different 2-peg cementless baseplates with smooth, mid, and high roughnesses and a 4-peg cement/ess baseplate with mid-roughness.

  4. Mechanical stability of roll-to-roll printed solar cells under cyclic bending and torsion

    DEFF Research Database (Denmark)

    Finn, Mickey; Martens, Christian James; Zaretski, Aliaksandr V.

    2018-01-01

    The ability of printed organic solar cells (OSCs) to survive repeated mechanical deformation is critical to large-scale implementation. This paper reports an investigation into the mechanical stability of OSCs through bending and torsion testing of whole printed modules. Two types of modules...... strain cycles. Failure during torsion occurs through crack propagation initiated at stress concentrations on the edges of the module that were imposed by their rectangular geometry and ultimately leads to bifurcation of the entire module. Rather than the differences in electrode materials...

  5. Targeted delivery of colloids by swimming bacteria

    Science.gov (United States)

    Koumakis, N.; Lepore, A.; Maggi, C.; Di Leonardo, R.

    2013-01-01

    The possibility of exploiting motile microorganisms as tiny propellers represents a fascinating strategy for the transport of colloidal cargoes. However, delivery on target sites usually requires external control fields to steer propellers and trigger cargo release. The need for a constant feedback mechanism prevents the design of compact devices where biopropellers could perform their tasks autonomously. Here we show that properly designed three-dimensional (3D) microstructures can define accumulation areas where bacteria spontaneously and efficiently store colloidal beads. The process is stochastic in nature and results from the rectifying action of an asymmetric energy landscape over the fluctuating forces arising from collisions with swimming bacteria. As a result, the concentration of colloids over target areas can be strongly increased or depleted according to the topography of the underlying structures. Besides the significance to technological applications, our experiments pose some important questions regarding the structure of stationary probability distributions in non-equilibrium systems. PMID:24100868

  6. Stabilization

    Directory of Open Access Journals (Sweden)

    Muhammad H. Al-Malack

    2016-07-01

    Full Text Available Fuel oil flyash (FFA produced in power and water desalination plants firing crude oils in the Kingdom of Saudi Arabia is being disposed in landfills, which increases the burden on the environment, therefore, FFA utilization must be encouraged. In the current research, the effect of adding FFA on the engineering properties of two indigenous soils, namely sand and marl, was investigated. FFA was added at concentrations of 5%, 10% and 15% to both soils with and without the addition of Portland cement. Mixtures of the stabilized soils were thoroughly evaluated using compaction, California Bearing Ratio (CBR, unconfined compressive strength (USC and durability tests. Results of these tests indicated that stabilized sand mixtures could not attain the ACI strength requirements. However, marl was found to satisfy the ACI strength requirement when only 5% of FFA was added together with 5% of cement. When the FFA was increased to 10% and 15%, the mixture’s strength was found to decrease to values below the ACI requirements. Results of the Toxicity Characteristics Leaching Procedure (TCLP, which was performed on samples that passed the ACI requirements, indicated that FFA must be cautiously used in soil stabilization.

  7. Experimental study of the mechanical stabilization of electric arc furnace dust using fluid cement mortars.

    Science.gov (United States)

    Ledesma, E F; Jiménez, J R; Ayuso, J; Fernández, J M; Brito, J de

    2017-03-15

    This article shows the results of an experimental study carried out in order to determine the maximum amount of electric arc furnace dust (EAFD) that can be incorporated into fluid cement-based mortars to produce mechanically stable monolithic blocks. The leaching performance of all mixes was studied in order to classify them according to the EU Council Decision 2003/33/EC. Two mortars were used as reference and three levels of EAFD incorporation were tested in each of the reference mortars. As the incorporation ratio of EAFD/cement increases, the mechanical strength decreases. This is due to the greater EAFD/cement and water/cement ratios, besides the presence of a double-hydrated hydroxide of Ca and Zn (CaZn2(OH)6·2H2O) instead of the portlandite phase (Ca(OH)2) in the mixes made with EAFD, as well as non-hydrated tricalcium silicate. A mass ratio of 2:1 (EAFD: cement-based mortar) can be added maintaining a stable mechanical strength. The mechanical stabilization process also reduced the leaching of metals, although it was not able to reduce the Pb concentration below the limit for hazardous waste. The high amount of EAFD mechanically stabilized in this experimental study can be useful to reduce the storage volume required in hazardous waste landfills.

  8. Study of the mechanisms of the flame propagation and stabilization in porous media

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The CH4/air premixed gas combustion processes in porous media were numerically studied using the two-temperature reacting fluid model with dispersions and detailed chemical reaction mechanism GRI 3.0. The mechanisms of the propagation and stabilization of submerge flames and surface flames in porous media were illuminated distinctly by considering the magnitude of the terms in the two energy equations, analyzing the sensibility of flame propagation speed to flame location, heat exchange coefficient between gas and solid, thermal conductivity and radiative extinction coefficient of porous media. It was concluded that the propagation mechanism of a submerged flame is similar to that of a free flame with an additional preheat zone and that the surface-flame propagation mechanism in porous media is similar to that of a free flame with heat loss in reaction zone.

  9. Enhanced mechanical behavior of a nanocrystallised stainless steel and its thermal stability

    Energy Technology Data Exchange (ETDEWEB)

    Roland, T. [ICD, LASMIS, University of Technology of Troyes, 10010 Troyes (France); Retraint, D. [ICD, LASMIS, University of Technology of Troyes, 10010 Troyes (France)]. E-mail: delphine.retraint@utt.fr; Lu, K. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015 (China); Lu, J. [Department of Mechanical Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (China)

    2007-02-15

    This paper discusses the mechanical properties of a nanocrystallised stainless steel obtained using surface mechanical attrition treatment (SMAT) and the underlying grain refinement mechanism using transmission electron microscopy (TEM). It was shown that grain refinement down to the nanometer range has the potential to significantly improve the mechanical properties of a 316L stainless steel which becomes comparable in strength to titanium alloys. Hence, promising structural applications could be considered for such a material. At the same time, the thermal stability of this nanocrystallised material was studied in the temperature range from 100 to 800 deg. C. The results show that the nanometer scaled microstructure is retained up to 600 deg. C and that a controlled annealing treatment could even lead to enhancement of both strength and ductility of this material. All these results are explained in terms of microstructural investigations, X-ray diffraction measurements, tensile and bending tests as well as microhardness measurements.

  10. Colloidal Gold--Collagen Protein Core--Shell Nanoconjugate: One-Step Biomimetic Synthesis, Layer-by-Layer Assembled Film, and Controlled Cell Growth.

    Science.gov (United States)

    Xing, Ruirui; Jiao, Tifeng; Yan, Linyin; Ma, Guanghui; Liu, Lei; Dai, Luru; Li, Junbai; Möhwald, Helmuth; Yan, Xuehai

    2015-11-11

    The biogenic synthesis of biomolecule-gold nanoconjugates is of key importance for a broad range of biomedical applications. In this work, a one-step, green, and condition-gentle strategy is presented to synthesize stable colloidal gold-collagen core-shell nanoconjugates in an aqueous solution at room temperature, without use of any reducing agents and stabilizing agents. It is discovered that electrostatic binding between gold ions and collagen proteins and concomitant in situ reduction by hydroxyproline residues are critically responsible for the formation of the core-shell nanoconjugates. The film formed by layer-by-layer assembly of such colloidal gold-collagen nanoconjugates can notably improve the mechanical properties and promote cell adhesion, growth, and differentiation. Thus, the colloidal gold-collagen nanoconjugates synthesized by such a straightforward and clean manner, analogous to a biomineralization pathway, provide new alternatives for developing biologically based hybrid biomaterials toward a range of therapeutic and diagnostic applications.

  11. Mechanism of enhanced mechanical stability of a minimal RNA kissing complex elucidated by nonequilibrium molecular dynamics simulations.

    Science.gov (United States)

    Chen, Alan A; García, Angel E

    2012-06-12

    An RNA kissing loop from the Moloney murine leukemia virus (MMLV) exhibits unusual mechanical stability despite having only two intermolecular base pairs. Mutations at this junction have been shown to destabilize genome dimerization, with concomitant reductions in viral packaging efficiency and infectivity. Optical tweezers experiments have shown that it requires as much force to break the MMLV kissing-loop complex as is required to unfold an 11-bp RNA hairpin [Li PTX, Bustamante C, Tinoco I (2006) Proc Natl Acad Sci USA 103:15847-15852]. Using nonequilibrium all-atom molecular dynamics simulations, we have developed a detailed model for the kinetic intermediates of the force-induced dissociation of the MMLV dimerization initiation site kissing loop. Two hundred and eight dissociation events were simulated (approximately 16 μs total simulation time) under conditions of constant applied external force, which we use to construct a Markov state model for kissing-loop dissociation. We find that the complex undergoes a conformational rearrangement, which allows for equal distribution of the applied force among all of the intermolecular hydrogen bonds, which is intrinsically more stable than the sequential unzipping of an ordinary hairpin. Stacking interactions with adjacent, unpaired loop adenines further stabilize the complex by increasing the repair rate of partially broken H-bonds. These stacking interactions are prominently featured in the transition state, which requires additional coordinates orthogonal to the end-to-end extension to be uniquely identified. We propose that these stabilizing features explain the unusual stability of other retroviral kissing-loop complexes such as the HIV dimerization site.

  12. Elucidating the mechanical effects of pore water pressure increase on the stability of unsaturated soil slopes

    Science.gov (United States)

    Buscarnera, G.

    2012-12-01

    The increase of the pore water pressure due to rain infiltration can be a dominant component in the activation of slope failures. This paper shows an application of the theory of material stability to the triggering analysis of this important class of natural hazards. The goal is to identify the mechanisms through which the process of suction removal promotes the initiation of mechanical instabilities. The interplay between increase in pore water pressure, and failure mechanisms is investigated at material point level. In order to account for multiple failure mechanisms, the second-order work criterion is used and different stability indices are devised. The paper shows that the theory of material stability can assess the risk of shear failure and static liquefaction in both saturated and unsaturated contexts. It is shown that the combined use of an enhanced definition of second-order work for unsaturated porous media and a hydro-mechanical constitutive framework enables to retrieve bifurcation conditions for water-infiltration processes in unsaturated deposits. This finding discloses the importance of the coupling terms that incorporate the interaction between the solid skeleton and the pore fluids. As a consequence, these theoretical results suggest that some material properties that are not directly associated with the shearing resistance (e.g., the potential for wetting compaction) can play an important role in the initiation of slope failures. According to the proposed interpretation, the process of pore pressure increase can be understood as a trigger of uncontrolled strains, which at material point level are reflected by the onset of bifurcation conditions.

  13. Stabilising emulsion-based colloidal structures with mixed food ingredients.

    Science.gov (United States)

    Dickinson, Eric

    2013-03-15

    The physical scientist views food as a complex form of soft matter. The complexity has its origin in the numerous ingredients that are typically mixed together and the subtle variations in microstructure and texture induced by thermal and mechanical processing. The colloid science approach to food product formulation is based on the assumption that the major product attributes such as appearance, rheology and physical stability are determined by the spatial distribution and interactions of a small number of generic structural entities (biopolymers, particles, droplets, bubbles, crystals) organised in various kinds of structural arrangements (layers, complexes, aggregates, networks). This review describes some recent advances in this field with reference to three discrete classes of dispersed systems: particle-stabilised emulsions, emulsion gels and aerated emulsions. Particular attention is directed towards explaining the crucial role of the macromolecular ingredients (proteins and polysaccharides) in controlling the formation and stabilisation of the colloidal structures. The ultimate objective of this research is to provide the basic physicochemical insight required for the reliable manufacture of novel structured foods with an appealing taste and texture, whilst incorporating a more healthy set of ingredients than those found in many existing traditional products.

  14. Separation of Organic Dyes from Water by Colloidal Gas Aphrons

    Institute of Scientific and Technical Information of China (English)

    黄颖怡; 王运东; 戴猷元

    2002-01-01

    Colloidal gas aphrons (CGAs) are micron-sized gas bubbles produced by stirring surfactant solutions at high speed. A single CGA dispersed in water is composed of a gaseous inner core, surrounded by a double water-soapy layer. CGAs have large interfacial area per unit volume and exhibit relatively high stability. These characteristics make CGAs very suitable in flotation systems. This paper studied the flotation of organic dyes from water using CGAs. The experimental results show that the flotation process may follow four mechanisms, i.e., ion coupling of the oppositely charged species of the surfactant forming the CGA and the organic dye, reactions between CGA and the organic dye, ion-dye complex adsorbed on the surface of CGAs, and hydrophilic or hydrophobic characteristics of the organic dyes.

  15. The Use of Polymer Design in Resorbable Colloids

    Science.gov (United States)

    Finne-Wistrand, Anna; Albertsson, Ann-Christine

    2006-08-01

    During the past decade, researchers in the field of polymer chemistry have developed a wide range of very powerful procedures for constructing ever-more-sophisticated polymers. These methods subsequently have been used in suitable systems to solve specific medical problems. This is complicated, and many key factors such as mechanical properties, biocompatibility, biodegradation, stability, and degradation profile must be considered. Colloid particle systems can be used to solve many biomedical- and pharmaceutical-related problems, and it is expected that nanotechnology can be used to develop these materials, devices, and systems even further. For example, an injectible scaffold system with a defined release and degradation profile has huge potential for the repair and regeneration of damaged tissues. This short, nonexhaustive review presents examples of polymer architecture in resorbable particles that have been compared and tested in biomedical applications. We also discuss the design of polymers for core-shell structures.

  16. MOBILIZATION AND CHARACTERIZATION OF COLLOIDS GENERATED FROM CEMENT LEACHATES MOVING THROUGH A SRS SANDY SEDIMENT

    Energy Technology Data Exchange (ETDEWEB)

    Li, D.; Roberts, K.; Kaplan, D.; Seaman, J.

    2011-09-20

    Naturally occurring mobile colloids are ubiquitous and are involved in many important processes in the subsurface zone. For example, colloid generation and subsequent mobilization represent a possible mechanism for the transport of contaminants including radionuclides in the subsurface environments. For colloid-facilitated transport to be significant, three criteria must be met: (1) colloids must be generated; (2) contaminants must associate with the colloids preferentially to the immobile solid phase (aquifer); and (3) colloids must be transported through the groundwater or in subsurface environments - once these colloids start moving they become 'mobile colloids'. Although some experimental investigations of particle release in natural porous media have been conducted, the detailed mechanisms of release and re-deposition of colloidal particles within natural porous media are poorly understood. Even though this vector of transport is known, the extent of its importance is not known yet. Colloid-facilitated transport of trace radionuclides has been observed in the field, thus demonstrating a possible radiological risk associated with the colloids. The objective of this study was to determine if cementitious leachate would promote the in situ mobilization of natural colloidal particles from a SRS sandy sediment. The intent was to determine whether cementitious surface or subsurface structure would create plumes that could produce conditions conducive to sediment dispersion and mobile colloid generation. Column studies were conducted and the cation chemistries of influents and effluents were analyzed by ICP-OES, while the mobilized colloids were characterized using XRD, SEM, EDX, PSD and Zeta potential. The mobilization mechanisms of colloids in a SRS sandy sediment by cement leachates were studied.

  17. Physical properties and stability mechanisms of poly(ethylene glycol) conjugated liposome encapsulated hemoglobin dispersions.

    Science.gov (United States)

    Arifin, Dian R; Palmer, Andre F

    2005-01-01

    Liposomes encapsulating hemoglobin (LEHs) surface-conjugated with 2000 and 550 Da poly(ethylene glycol) (PEG) were produced via extrusion through 400, 200 and 100 nm pore diameter membranes in two types of phosphate buffer with different ionic strengths. The lipid bilayers were composed of dimyristoyl-phosphatidylcholine (DMPC), cholesterol, dimyristoyl-phosphoethanolamine-PEG (DMPE-PEG), dimyristoyl-phosphatidylglycerol (DMPG), and alpha-tocopherol (in a 43:40:10:5:2 mole ratio). N-acetyl-L-cysteine was coencapsulated in order to suppress hemoglobin (Hb) oxidation. Various physical properties of PEG-LEH dispersions were determined: size distribution, encapsulation efficiency, P50 (partial pressure of O2 where half of the oxygen binding sites are saturated with O2), cooperativity coefficient, and encapsulated methemoglobin (MetHb) level. In order to study the stabilization mechanism of these dispersions, the effective bending constant (KB) and the spontaneous radius of curvature (R0) of PEG-LEHs were extracted by fitting a mathematical model describing the size distribution of a liposome dispersion to the experimentally measured size distributions. We observed that liposome dispersions extruded in phosphate buffer (PB) were more monodisperse than liposomes extruded in phosphate buffered saline (PBS), and higher molecular weight PEG promoted the formation of narrower size distributions. Moreover, extrusion in PB and lipid conjugation with higher molecular weight PEG imparted higher bilayer rigidity (high KB), and stabilized the liposome dispersions by the spontaneous curvature mechanism, whereas the other liposome dispersions were stabilized by thermal undulations (low KB). The P50 and cooperativity coefficient of PEG-LEHs extruded in PBS and PB was comparable to that of human blood, and the encapsulated MetHb levels were less than 5%. The highest encapsulation efficiencies obtained were 27%-36% (82-109 mg Hb/mL) for LEH dispersions extruded in PBS and grafted with

  18. Magnetic nanocarriers of doxorubicin coated with poly(ethylene glycol) and folic acid: relation between coating structure, surface properties, colloidal stability, and cancer cell targeting.

    Science.gov (United States)

    Kaaki, Karine; Hervé-Aubert, Katel; Chiper, Manuela; Shkilnyy, Andriy; Soucé, Martin; Benoit, Roland; Paillard, Archibald; Dubois, Pierre; Saboungi, Marie-Louise; Chourpa, Igor

    2012-01-17

    We report the efficient one-step synthesis and detailed physicochemical evaluation of novel biocompatible nanosystems useful for cancer therapeutics and diagnostics (theranostics). These systems are the superparamagnetic iron oxide nanoparticles (SPIONs) carrying the anticancer drug doxorubicin and coated with the covalently bonded biocompatible polymer poly(ethylene glycol) (PEG), native and modified with the biological cancer targeting ligand folic acid (PEG-FA). These multifunctional nanoparticles (SPION-DOX-PEG-FA) are designed to rationally combine multilevel mechanisms of cancer cell targeting (magnetic and biological), bimodal cancer cell imaging (by means of MRI and fluorescence), and bimodal cancer treatment (by targeted drug delivery and by hyperthermia effect). Nevertheless, for these concepts to work together, the choice of ingredients and particle structure are critically important. Therefore, in the present work, a detailed physicochemical characterization of the organic coating of the hybrid nanoparticles is performed by several surface-specific instrumental methods, including surface-enhanced Raman scattering (SERS) spectroscopy, X-ray photoelectron spectrometry (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). We demonstrate that the anticancer drug doxorubicin is attached to the iron oxide surface and buried under the polymer layers, while folic acid is located on the extreme surface of the organic coating. Interestingly, the moderate presence of folic acid on the particle surface does not increase the particle surface potential, while it is sufficient to increase the particle uptake by MCF-7 cancer cells. All of these original results contribute to the better understanding of the structure-activity relationship for hybrid biocompatible nanosystems and are encouraging for the applications in cancer theranostics.

  19. Colloidal pen lithography.

    Science.gov (United States)

    Xue, Mianqi; Cai, Xiaojing; Chen, Ghenfu

    2015-02-04

    Colloidal pen lithography, a low-cost, high-throughput scanning probe contact printing method, has been developed, which is based on self-assembled colloidal arrays embedded in a soft elastomeric stamp. Patterned protein arrays are demonstrated using this method, with a feature size ranging from 100 nm to several micrometers. A brief study into the specificity reorganization of protein gives evidence for the feasibility of this method for writing protein chips. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Solutions Stability of Initial Boundary Problem, Modeling of Dynamics of Some Discrete Continuum Mechanical System

    Directory of Open Access Journals (Sweden)

    D. A. Eliseev

    2015-01-01

    Full Text Available The solution stability of an initial boundary problem for a linear hybrid system of differential equations, which models the rotation of a rigid body with two elastic rods located in the same plane is studied in the paper. To an axis passing through the mass center of the rigid body perpendicularly to the rods location plane is applied the stabilizing moment proportional to the angle of the system rotation, derivative of the angle, integral of the angle. The external moment provides a feedback. A method of studying the behavior of solutions of the initial boundary problem is proposed. This method allows to exclude from the hybrid system of differential equations partial differential equations, which describe the dynamics of distributed elements of a mechanical system. It allows us to build one equation for an angle of the system rotation. Its characteristic equation defines the stability of solutions of all the system. In the space of feedback-coefficients the areas that provide the asymptotic stability of solutions of the initial boundary problem are built up.

  1. Thermal and mechanical stability of retained austenite in aluminum-containing multiphase TRIP steels

    CERN Document Server

    Zwaag, S; Kruijver, S O; Sietsma, J

    2002-01-01

    Stability of retained austenite is the key issue to understand transformation-induced plasticity (TRIP) effect. In this work, both thermal stability and mechanical stability are investigated by thermo-magnetic as well as in situ conventional X-ray diffraction and micro synchrotron radiation diffraction measurements. The thermal stability in a 0.20C-1.52Mn-0.25Si-0.96Al (wt%) TRIP steel is studied in the temperature range between 5 and 300 K under a constant magnetic field of 5T. It is found that almost all austenite transforms thermally to martensite upon cooling to 5K and M sub s and M sub f temperatures are analyzed to be 355 and 115 K. Transformation kinetics on the fraction versus temperature relation are well described by a model based on thermodynamics. From the in situ conventional X-ray and synchrotron diffraction measurements in a 0.17C-1.46Mn-0.26Si-1.81Al (wt%) steel, the volume fraction of retained austenite is found to decrease as the strain increases according to Ludwigson and Berger relation. T...

  2. Mechanical synthesis of copper-carbon nanocomposites: Structural changes, strengthening and thermal stabilization

    Energy Technology Data Exchange (ETDEWEB)

    Nunes, D., E-mail: daniela.nunes@ist.utl.pt [Associacao Euratom/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); LNEG, Estrada do Paco do Lumiar, 1649-038 Lisboa (Portugal); ICEMS, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Livramento, V. [Associacao Euratom/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); LNEG, Estrada do Paco do Lumiar, 1649-038 Lisboa (Portugal); Mateus, R. [Associacao Euratom/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Correia, J.B. [LNEG, Estrada do Paco do Lumiar, 1649-038 Lisboa (Portugal); Alves, L.C. [ITN, Instituto Tecnologico e Nuclear, Estrada Nacional 10, 2686-953 Sacavem (Portugal); Vilarigues, M. [Departamento de Conservacao e Restauro e R and D Unit Vidro e da Ceramica Para as Artes, FCT-UNL, Quinta da Torre, 2829-516 Caparica (Portugal); Carvalho, P.A. [ICEMS, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Departamento de Bioengenharia, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal)

    2011-11-15

    Highlights: {yields} The study characterized Cu-nanodiamond (Cu-nD) and Cu-graphite (Cu-G) composites. {yields} Preservation of nD crystalline structure during high-energy milling was demonstrated. {yields} Higher refinement of matrix in Cu-nD comparing to Cu-G is due to a milling mechanism. {yields} Remarkable thermal stability and microhardness have been achieved in Cu-nD and Cu-G. {yields} Strengthening resulted mainly from grain refinement and second-phase reinforcement. - Abstract: Processing of copper-carbon nanocomposites by mechanical synthesis poses specific challenges as carbon phases are prone to amorphization and exhibit an intrinsically difficult bonding with copper. The present work investigates Cu-nanodiamond (Cu-nD) and Cu-graphite (Cu-G) composites produced by mechanical synthesis and subsequent heat treatments. Transmission electron microscopy observations showed homogeneous particle distributions and intimate bonding between the metallic matrix and the carbon phases. Ring diffraction patterns of chemically extracted carbon phases demonstrated that milled nanodiamond preserved crystallinity, while an essentially amorphous nature could be inferred for milled graphite. Raman spectra confirmed that nanodiamond particles remained essentially unaffected by the mechanical synthesis, whereas the bands of milled graphite were significantly changed into the typical amorphous carbon fingerprint. Particle-induced X-ray emission spectroscopy showed that the total contamination originating from the milling media remained below 0.7 wt.%. The Cu-nanodiamond composite exhibited remarkable microhardness and microstructural thermal stability when compared with pure nanostructured copper.

  3. Ultrasonic, Molecular and Mechanical Testing Diagnostics in Natural Fibre Reinforced, Polymer-Stabilized Earth Blocks

    Directory of Open Access Journals (Sweden)

    C. Galán-Marín

    2013-01-01

    Full Text Available The aim of this research study was to evaluate the influence of utilising natural polymers as a form of soil stabilization, in order to assess their potential for use in building applications. Mixtures were stabilized with a natural polymer (alginate and reinforced with wool fibres in order to improve the overall compressive and flexural strength of a series of composite materials. Ultrasonic pulse velocity (UPV and mechanical strength testing techniques were then used to measure the porous properties of the manufactured natural polymer-soil composites, which were formed into earth blocks. Mechanical tests were carried out for three different clays which showed that the polymer increased the mechanical resistance of the samples to varying degrees, depending on the plasticity index of each soil. Variation in soil grain size distributions and Atterberg limits were assessed and chemical compositions were studied and compared. X-ray diffraction (XRD, X-ray fluorescence spectroscopy (XRF, and energy dispersive X-ray fluorescence (EDXRF techniques were all used in conjunction with qualitative identification of the aggregates. Ultrasonic wave propagation was found to be a useful technique for assisting in the determination of soil shrinkage characteristics and fibre-soil adherence capacity and UPV results correlated well with the measured mechanical properties.

  4. Method and Mechanisms of Soil Stabilization Using Electric Arc Furnace Dust

    Science.gov (United States)

    Al-Amoudi, Omar S. Baghabra; Al-Homidy, Abdullah A.; Maslehuddin, Mohammed; Saleh, Tawfik A.

    2017-04-01

    This paper reports the method and mechanism for improving the strength of marl and desert sand utilizing electric arc furnace dust (EAFD), an industrial by-product, in lieu of cement or lime. EAFD was used in conjunction with a small quantity (2%) of cement. The mechanical properties and durability characteristics of marl and sand mixed with 2% cement plus 5-, 10-, 20- or 30%-EAFD, by weight of the soil, were evaluated. The soil-cement-EAFD mixtures were used to determine their unconfined compressive strength (UCS), soaked California Bearing Ratio (CBR) and durability. The risk of leaching of toxic heavy metals, such as lead and cadmium, from the stabilized soils to the groundwater was also investigated. The mechanisms of stabilization of the selected soils due to the use of EAFD along with a small quantity of cement are also elucidated. The usage of 20 to 30% EAFD with 2% cement was noted to considerably improve the mechanical properties and durability of both marl and sand.

  5. Characterization of an injectable, degradable polymer for mechanical stabilization of mandibular fractures.

    Science.gov (United States)

    Henslee, Allan M; Yoon, Diana M; Lu, Benjamin Y; Yu, Joseph; Arango, Andrew A; Marruffo, Liann P; Seng, Luke; Anver, Tamir D; Ather, Hunaiza; Nair, Manitha B; Piper, Sean O; Demian, Nagi; Wong, Mark E K; Kasper, F Kurtis; Mikos, Antonios G

    2015-04-01

    This study investigated the use of injectable poly(propylene fumarate) (PPF) formulations for mandibular fracture stabilization applications. A full factorial design with main effects analysis was employed to evaluate the effects of the PPF:N-vinyl pyrrolidone (NVP, crosslinking agent) ratio and dimethyl toluidine (DMT, accelerator) concentration on key physicochemical properties including setting time, maximum temperature, mechanical properties, sol fraction, and swelling ratio. Additionally, the effects of formulation crosslinking time on the mechanical and swelling properties were investigated. The results showed that increasing the PPF:NVP ratio from 3:1 to 4:1 or decreasing the DMT concentration from 0.05 to 0.01 v/w % significantly decreased all mechanical properties as well as significantly increased the sol fraction and swelling ratio. Also, increasing the crosslinking time at 37°C from 1 to 7 days significantly increased all mechanical properties and decreased both the sol fraction and swelling ratio. This study further showed that the flexural stiffness of ex vivo stabilized rabbit mandibles increased from 1.7 ± 0.3 N/mm with a traditional mini-plate fixator to 14.5 ± 4.1 N/mm for the 4:1 (0.05 v/w % DMT) PPF formulation at day 1. Overall, the formulations tested in this study were found to have properties suitable for potential further consideration in mandibular fracture fixation applications. © 2014 Wiley Periodicals, Inc.

  6. Curing Mechanism of Condensed Polynuclear Aromatic Resin and Thermal Stability of Cured Resin

    Institute of Scientific and Technical Information of China (English)

    Li Shibin; Sun Qiqian; Wang Yuwei; Wu Mingbo; Zhang Zailong

    2015-01-01

    In order to improve the thermal stability of condensed polynuclear aromatic (COPNA) resin synthesized from vacuum residue, 1,4-benzenedimethanol was added to cure COPNA resin. The curing mechanism was investigated by pro-ton nuclear magnetic resonance spectrometry, solid carbon-13 nuclear magnetic resonance spectrometry and Fourier trans-form infrared spectroscopy. Microstructures of the uncured and the cured COPNA resins were studied by scanning electron microscopy and X-ray diffractometry. The thermal stability of COPNA resins before and after curing was tested by thermo-gravimetric analysis. The element composition of the cured COPNA resin heated at different temperatures was analyzed by an element analyzer. The results showed that the uncured COPNA resin reacted with the cross-linking agent during the cur-ing process, and the curing mechanism was conifrmed to be the electrophilic substitution reaction. Compared with the un-cured COPNA resin, the cured COPNA resin had a smooth surface, well-ordered and streamlined sheet structure with more crystalline solids, better molecular arrangement and orientation. The weight loss process of the uncured and cured COPNA resins was divided into three stages. Carbon residue of the cured COPNA resin was 41.65%at 600℃, which was much higher than 25.02%of the uncured COPNA resin, which indicated that the cured COPNA resin had higher thermal stability.

  7. Organic fraction of municipal solid waste from mechanical selection: biological stabilization and recovery options.

    Science.gov (United States)

    Cesaro, Alessandra; Russo, Lara; Farina, Anna; Belgiorno, Vincenzo

    2016-01-01

    Although current trends address towards prevention strategies, the organic fraction of municipal solid waste is greatly produced, especially in high-income contexts. Its recovery-oriented collection is a common practice, but a relevant portion of the biodegradable waste is not source selected. Mechanical and biological treatments (MBT) are the most common option to sort and stabilize the biodegradable matter ending in residual waste stream. Following the changes of the framework around waste management, this paper aimed at analyzing the quality of the mechanically selected organic waste produced in MBT plants, in order to discuss its recovery options. The material performance was obtained by its composition as well as by its main chemical and physical parameters; biological stability was also assessed by both aerobic and anaerobic methods. On this basis, the effectiveness of an aerobic biostabilization process was assessed at pilot scale. After 21 days of treatment, results proved that the biomass had reached an acceptable biostabilization level, with a potential Dynamic Respirometric Index (DRIP) value lower than the limit required for its use as daily or final landfill cover material. However, the final stabilization level was seen to be influenced by scaling factors and the 21 days of treatment turned to be not so adequate when applied in the existing full-scale facility.

  8. Detecting Selection on Protein Stability through Statistical Mechanical Models of Folding and Evolution

    Directory of Open Access Journals (Sweden)

    Ugo Bastolla

    2014-03-01

    Full Text Available The properties of biomolecules depend both on physics and on the evolutionary process that formed them. These two points of view produce a powerful synergism. Physics sets the stage and the constraints that molecular evolution has to obey, and evolutionary theory helps in rationalizing the physical properties of biomolecules, including protein folding thermodynamics. To complete the parallelism, protein thermodynamics is founded on the statistical mechanics in the space of protein structures, and molecular evolution can be viewed as statistical mechanics in the space of protein sequences. In this review, we will integrate both points of view, applying them to detecting selection on the stability of the folded state of proteins. We will start discussing positive design, which strengthens the stability of the folded against the unfolded state of proteins. Positive design justifies why statistical potentials for protein folding can be obtained from the frequencies of structural motifs. Stability against unfolding is easier to achieve for longer proteins. On the contrary, negative design, which consists in destabilizing frequently formed misfolded conformations, is more difficult to achieve for longer proteins. The folding rate can be enhanced by strengthening short-range native interactions, but this requirement contrasts with negative design, and evolution has to trade-off between them. Finally, selection can accelerate functional movements by favoring low frequency normal modes of the dynamics of the native state that strongly correlate with the functional conformation change.

  9. Bio-geochemical mechanisms influencing the stability of As-bearing iron oxides

    Science.gov (United States)

    Garrido, F.; Dictor, M. C.; Morin, G.; Bodénan, F.; Baranger, P.

    2003-04-01

    Hydrous Ferric Oxydes (HFO) often occurring in the organo-mineral matrix of soils and sediments act as a preferential substrate for the fixation of toxic metals and metalloids as arsenic. The chemical stability of these complexes strongly depends on the physico-chemical and biological conditions of the medium. In this context, the aim of this work was to study mobility factors of arsenic by analogy with bio-geochemical reactions involved in soils and sediments. We studied the conditions of arsenic release in solution upon the reaction of synthetic As-doped iron-oxide minerals with specific micro-organisms (Fe(III)-reducing bacteria or As(V)-reducing bacteria) under controlled laboratory conditions. Our results showed that As release in solution proceeds in two step. First, a rapid As release in solution is caused by competitive sorption processes with other oxy-anions present in the culture medium. In a second step, the microbial reduction of Fe(III) and/or As(V) become the main factor affecting the stability of the As-iron oxide complexes. These two mechanisms were regulated by the physico-chemical conditions of the medium (pH, Eh and phosphate concentration). These results should help in a better understanding of the arsenic mobility in polluted environment. They confirm the major influence of the biological factor on the stability of the As trapping by HFO. This latter chemical trapping mechanism being involved in numerous As water-treatment processes.

  10. Colloidal crystals of core-shell type spheres with poly(styrene) core and poly(ethylene oxide) shell.

    Science.gov (United States)

    Okamoto, Junichi; Kimura, Hiroshi; Tsuchida, Akira; Okubo, Tsuneo; Ito, Koichi

    2007-04-15

    Elastic modulus and crystal growth kinetics have been studied for colloidal crystals of core-shell type colloidal spheres (diameter=160-200 nm) in aqueous suspension. Crystallization properties of three kinds of spheres, which have poly(styrene) core and poly(ethylene oxide) shell with different oxyethylene chain length (n=50, 80 and 150), were examined by reflection spectroscopy. The suspensions were deionized exhaustively for more than 1 year using mixed bed of ion-exchange resins. The rigidities of the crystals range from 0.11 to 120 Pa and from 0.56 to 76 Pa for the spheres of n=50 and 80, respectively, and increase sharply as the sphere volume fraction increase. The g factor, parameter for crystal stability, range from 0.029 to 0.13 and from 0.040 to 0.11 for the spheres of n=50 and 80, respectively. These g values indicate the formation of stable crystals, and the values were decreased as the sphere volume fraction increased. Two components of crystal growth rate coefficients, fast and slow, were observed in the order from 10(-3) to 10(1)s(-1). This is due to the secondary process in the colloidal crystallization mechanism, corresponding to reorientation from metastable crystals formed in the primary process and/or Ostwald-ripening process. There are no distinct differences in the structural, kinetic and elastic properties among the colloidal crystals of the different core-shell size spheres, nor difference between those of core-shell spheres and silica or poly(styrene) spheres. The results are very reasonably interpreted by the fact that colloidal crystals are formed in a closed container owing to long-range repulsive forces and the Brownian movement of colloidal spheres surrounded by extended electrical double layers, and their formation is not influenced by the rigidity and internal structure of the spheres.

  11. Comparison between Specific Lumber Mobilization and Core-Stability Exercises with Core-Stability Exercises Alone in Mechanical low back pain

    OpenAIRE

    Ahmed, Rafiq; Shakil-ur-Rehman, Syed; Sibtain, Fozia

    2014-01-01

    Objective: To Compare the Specific Lumber Mobilization (SLM) techniques and Core-Stability (CS) Exercises with Core-Stability Exercises Alone in Mechanical low back pain (MLP) Methods: A 6 month pretest-posttest design, quasi experimental study was conducted at department of physiotherapy Khyber Teaching Hospital (KTH) Peshawar, Pakistan. We conveniently selected a sample 40 patients and placed into two groups. The SLM techniques with CS exercises was applied in group A and CS exercises alone...

  12. About the mechanical stability of MnFe(P,Si,B) giant-magnetocaloric materials

    Energy Technology Data Exchange (ETDEWEB)

    Guillou, F., E-mail: f.guillou@tudelft.nl [FAME, Faculty of Applied Sciences, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands); Yibole, H.; Dijk, N.H. van [FAME, Faculty of Applied Sciences, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands); Zhang, L. [BASF Netherlands B.V., Strijkviertel 67, 3454 PK De Meern (Netherlands); Hardy, V. [CRISMAT, Ensicaen, UMR 6508 CNRS, 6 B" d Maréchal Juin, 14050 Caen Cedex (France); Brück, E. [FAME, Faculty of Applied Sciences, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands)

    2014-12-25

    Highlights: • Electrical resistivity and hardness show an evolution at T{sub C} with thermal cycling. • Degradation depends on the (c/a) lattice discontinuity at the transition. • Boron substituted materials present an improved mechanical stability. - Abstract: Due to its ability to control the latent heat and the hysteresis (thermal or magnetic) at the first-order transition (FOT) without deteriorating the saturation magnetisation, boron substitution in MnFe(P,Si) materials has recently been reported to be an ideal parameter to reach promising magnetocaloric performances: ΔS ≈ 10 Jkg{sup −1} K{sup −1} and cyclic ΔT of 2.6 K (and more) at a moderate magnetic field of ΔB = 1 T. Additionally, an interesting aspect for applications is the improvement of the mechanical stability in B doped materials compared to the pristine MnFe(P,Si) compounds. These improved mechanical properties were initially supported by naked-eye inspection and the observation of a constant ΔT during a few thousands of magnetic cycles. (Guillou et al., 2014) Here, the evolution upon cycling of MnFe(P,Si,B) materials is studied in a more quantitative and systematic manner. For that purpose transformation temperatures, electrical resistivity, micro-hardness and the microstructure are tracked as a function of the thermal cycling across the FOT for three prototypical compositions in the MnFe(P,Si,B) system. It turns out this set of data confirms the initial finding that B substitution has a positive effect on the mechanical stability. The origin of this improvement is discussed, in particular in respect to the lattice parameter discontinuities at the phase transition.

  13. Intrinsic mechanisms stabilize encoding and retrieval circuits differentially in a hippocampal network model.

    Science.gov (United States)

    Hummos, Ali; Franklin, Charles C; Nair, Satish S

    2014-12-01

    Acetylcholine regulates memory encoding and retrieval by inducing the hippocampus to switch between pattern separation and pattern completion modes. However, both processes can introduce significant variations in the level of network activity and potentially cause a seizure-like spread of excitation. Thus, mechanisms that keep network excitation within certain bounds are necessary to prevent such instability. We developed a biologically realistic computational model of the hippocampus to investigate potential intrinsic mechanisms that might stabilize the network dynamics during encoding and retrieval. The model was developed by matching experimental data, including neuronal behavior, synaptic current dynamics, network spatial connectivity patterns, and short-term synaptic plasticity. Furthermore, it was constrained to perform pattern completion and separation under the effects of acetylcholine. The model was then used to investigate the role of short-term synaptic depression at the recurrent synapses in CA3, and inhibition by basket cell (BC) interneurons and oriens lacunosum-moleculare (OLM) interneurons in stabilizing these processes. Results showed that when CA3 was considered in isolation, inhibition solely by BCs was not sufficient to control instability. However, both inhibition by OLM cells and short-term depression at the recurrent CA3 connections stabilized the network activity. In the larger network including the dentate gyrus, the model suggested that OLM inhibition could control the network during high cholinergic levels while depressing synapses at the recurrent CA3 connections were important during low cholinergic states. Our results demonstrate that short-term plasticity is a critical property of the network that enhances its robustness. Furthermore, simulations suggested that the low and high cholinergic states can each produce runaway excitation through unique mechanisms and different pathologies. Future studies aimed at elucidating the circuit

  14. Effect Mechanism of Structure-Changed Water on Heat Stability of Lysozyme

    Institute of Scientific and Technical Information of China (English)

    赵林; 谭欣

    2003-01-01

    Based on the mechanism of the effect of hydration on the heat stability of lysozyme and the theory of water molecule clusters, the effect of structure-changed water on heat stability of lysozyme has been studied. The results obtained by differential scanning calorimetry (DSC) showed that the thermal denaturation temperature of lysozyme had been elevated 8.47 K through hydration of lysozyme with processed water whose structure had been changed so it was called "structured water" compared to ordinary water. The reason is that structured water changed the dipole moment of water molecules and easily formed cyclic water hexamer or cage-like water hexamer, so that the interacting force of maintaining three-dimensional conformation of lysozyme could be reinforced.

  15. Mechanical and Vacuum Stability Design Criteria for the LHC Experimental Vacuum Chambers

    CERN Document Server

    Collins, I R; Lepeule, P; Veness, R J M

    1998-01-01

    Four colliding beam experiments are planned for the Large Hadron Collider (LHC) requiring experimental vacuum chambers in the interaction region. The beam pipe should be as transparent as possible to scattered particles and detectors should be as close as possible to the interaction point, resulting in small diameter beam pipes. This, together with the bunched beam structure, makes ion induced pre ssure bump instability, well known from the Intersecting Storage Rings (ISR) at CERN, a potential problem. Adequate conductance, cleanliness of the beam pipes and efficient pumping are required to avo id this instability. Suppression of electron multipacting requires appropriate surface coatings and cleaning procedures. Small beam pipe diameters must provide the required beam stay clear and still a llow margin for alignment and stability inside detectors. Design criteria to ensure both local and global stability under static and dynamic mechanical loads are defined.

  16. On stability of NiTi wire during thermo-mechanical cycling

    Indian Academy of Sciences (India)

    C N Saikrishna; K V Ramaiah; S Allam Prabhu; S K Bhaumik

    2009-06-01

    The use of NiTi wire as thermal actuator involves repeated thermal cycling through the transformation range under a constant or fluctuating load. The stability of the material under such conditions has been a concern for the past many years. Experimental results show that for a given alloy composition, the repetitive functional behaviour of NiTi wire is largely dependent on the processing schedule/parameters and the stress–strain regime of thermo-mechanical cycling (TMC). Among the various processing parameters, retained cold work in the material and the shape memory annealing temperature/time have significant influence. It has been shown in the present study that for a stable functional behaviour, the material needs to be tailored through judicious selection of these parameters. Study also shows that, after processing, the material requires an additional stabilization treatment for ensuring minimal variation in the repetitive functional response upon TMC.

  17. Blocking effect of colloids on arsenate adsorption during co-transport through saturated sand columns.

    Science.gov (United States)

    Ma, Jie; Guo, Huaming; Lei, Mei; Wan, Xiaoming; Zhang, Hanzhi; Feng, Xiaojuan; Wei, Rongfei; Tian, Liyan; Han, Xiaokun

    2016-06-01

    Transport of environmental pollutants through porous media is influenced by colloids. Co-transport of As(V) and soil colloids at different pH were systematically investigated by monitoring breakthrough curves (BTCs) in saturated sand columns. A solute transport model was applied to characterize transport and retention sites of As(V) in saturated sand in the presence of soil colloids. A colloid transport model and the DLVO theory were used to reveal the mechanism and hypothesis of soil colloid-promoted As(V) transport in the columns. Results showed that rapid transport of soil colloids, regulated by pH and ionic strength, promoted As(V) transport by blocking As(V) adsorption onto sand, although soil colloids had low adsorption for As(V). The promoted transport was more significant at higher concentrations of soil colloids (between 25 mg L(-1) and 150 mg L(-1)) due to greater blocking effect on As(V) adsorption onto the sand surfaces. The blocking effect of colloids was explained by the decreases in both instantaneous (equilibrium) As adsorption and first-order kinetic As adsorption on the sand surface sites. The discovery of this blocking effect improves our understanding of colloid-promoted As transport in saturated porous media, which provides new insights into role of colloids, especially colloids with low As adsorption capacity, in As transport and mobilization in soil-groundwater systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. Medical applications of colloids

    CERN Document Server

    Matijevic, Egon

    2008-01-01

    The first book of its type on the medical and biomedical applications of colloids, although there are some related titles on different topicsDiscusses the effects of uniform particles in drug formulations and releaseEvaluates particle transport and deposition in the human body.

  19. Liquid crystal colloids

    Directory of Open Access Journals (Sweden)

    2010-01-01

    Full Text Available This special issue of "Condensed Matter Physics" focuses on the most recent developments in the study of a fascinating soft matter system, representing colloidal particles in a liquid crystalline environment. Furthermore, some articles address pioneering steps in the discovery of liquid crystals going back to 1861 paper by Julius Planer.

  20. Nucleation in food colloids

    Science.gov (United States)

    Povey, Malcolm J. W.

    2016-12-01

    Nucleation in food colloids has been studied in detail using ultrasound spectroscopy. Our data show that classical nucleation theory (CNT) remains a sound basis from which to understand nucleation in food colloids and analogous model systems using n-alkanes. Various interpretations and modifications of CNT are discussed with regard to their relevance to food colloids. Much of the evidence presented is based on the ultrasound velocity spectrometry measurements which has many advantages for the study of nucleating systems compared to light scattering and NMR due to its sensitivity at low solid contents and its ability to measure true solid contents in the nucleation and early crystal growth stages. Ultrasound attenuation spectroscopy also responds to critical fluctuations in the induction region. We show, however, that a periodic pressure fluctuation such as a quasi-continuous (as opposed to a pulse comprising only a few pressure cycles) ultrasound field can alter the nucleation process, even at very low acoustic intensity. Thus care must be taken when using ultrasound techniques that the measurements do not alter the studied processes. Quasi-continuous ultrasound fields may enhance or suppress nucleation and the criteria to determine such effects are derived. The conclusions of this paper are relevant to colloidal systems in foods, pharmaceuticals, agro-chemicals, cosmetics, and personal products.