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Sample records for monodisperse colloidal spheres

  1. Sustainable and scalable production of monodisperse and highly uniform colloidal carbonaceous spheres using sodium polyacrylate as the dispersant.

    Science.gov (United States)

    Gong, Yutong; Xie, Lei; Li, Haoran; Wang, Yong

    2014-10-28

    Monodisperse, uniform colloidal carbonaceous spheres were fabricated by the hydrothermal treatment of glucose with the help of a tiny amount of sodium polyacrylate (PAANa). This synthetic strategy is effective at high glucose concentration and for scale-up experiments. The sphere size can be easily tuned by the reaction time, temperature and glucose concentration.

  2. A Continuous Time Random Walk Description of Monodisperse, Hard-Sphere Colloids below the Ordering Transition

    Science.gov (United States)

    Lechman, Jeremy; Pierce, Flint

    2012-02-01

    Diffusive transport is a ubiquitous process that is typically understood in terms of a classical random walk of non-interacting particles. Here we present the results for a model of hard-sphere colloids in a Newtonian incompressible solvent at various volume fractions below the ordering transition (˜50%). We numerically simulate the colloidal systems via Fast Lubrication Dynamics -- a Brownian Dynamics approach with corrected mean-field hydrodynamic interactions. Colloid-colloid interactions are also included so that we effectively solve a system of interacting Langevin equations. The results of the simulations are analyzed in terms of the diffusion coefficient as a function of time with the early and late time diffusion coefficients comparing well with experimental results. An interpretation of the full time dependent behavior of the diffusion coefficient and mean-squared displacement is given in terms of a continuous time random walk. Therefore, the deterministic, continuum diffusion equation which arises from the discrete, interacting random walkers is presented. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  3. Lock and key colloids through polymerization-induced buckling of monodisperse silicon oil droplets

    NARCIS (Netherlands)

    Sacanna, S.|info:eu-repo/dai/nl/311471676; Irvine, W.T.M.; Rossi, L.|info:eu-repo/dai/nl/314410376; Pine, D.J.

    2011-01-01

    We have developed a new simple method to fabricate bulk amounts of colloidal spheres with well defined cavities from monodisperse emulsions. Herein, we describe the formation mechanism of ‘‘reactive’’ silicon oil droplets that deform to reproducible shapes via a polymerization-induced buckling

  4. A general approach for monodisperse colloidal perovskites, Chemistry of Materials

    NARCIS (Netherlands)

    Demirors, A.F.; Imhof, A.

    2009-01-01

    We describe a novel general method for synthesizing monodisperse colloidal perovskite particles at room temperature by postsynthesis addition of metal hydroxides to amorphous titania colloids. In previous work, we used titania particles to synthesize homogenously mixed silica-titania composite parti

  5. Apparent wall-slip of colloidal hard-sphere suspensions in microchannel flow

    NARCIS (Netherlands)

    Ghosh, Somnath; van den Ende, Henricus T.M.; Mugele, Friedrich Gunther; Duits, Michael H.G.

    2016-01-01

    We investigated the dependence of the apparent slip length (β) on the particle concentration for suspensions of colloidal hard spheres flowing through microchannels with smooth walls. Hydrostatic pressure was used to pump monodisperse suspensions of 1 μm silica spheres in water–glycerol mixture thro

  6. Preparation of polystyrene spheres in different particle sizes and assembly of the PS colloidal crystals

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Monodisperse polystyrene (PS) colloidal spheres were successfully prepared through emulsifier-free emulsion polymerization by controlling the polymerization reaction time, ionic strength of the system, concentration of the ionic copolymer (sodium p-styrenesulfonate) and other factors. The PS colloidal spheres were assembled into colloidal crystals whose structures were mainly face-centered cubic (fcc) close-packed. Then FDTD method was used to calculate the color-rendering characteristics of the colloidal crystals surface. The calculated results were consistent with the experimental results.

  7. Facile Synthesis of Monodispersed Polysulfide Spheres for Building Structural Colors with High Color Visibility and Broad Viewing Angle.

    Science.gov (United States)

    Li, Feihu; Tang, Bingtao; Wu, Suli; Zhang, Shufen

    2017-01-01

    The synthesis and assembly of monodispersed colloidal spheres are currently the subject of extensive investigation to fabricate artificial structural color materials. However, artificial structural colors from general colloidal crystals still suffer from the low color visibility and strong viewing angle dependence which seriously hinder their practical application in paints, colorimetric sensors, and color displays. Herein, monodispersed polysulfide (PSF) spheres with intrinsic high refractive index (as high as 1.858) and light-absorbing characteristics are designed, synthesized through a facile polycondensation and crosslinking process between sodium disulfide and 1,2,3-trichloropropane. Owing to their high monodispersity, sufficient surface charge, and good dispersion stability, the PSF spheres can be assembled into large-scale and high-quality 3D photonic crystals. More importantly, high structural color visibility and broad viewing angle are easily achieved because the unique features of PSF can remarkably enhance the relative reflectivity and eliminate the disturbance of scattering and background light. The results of this study provide a simple and efficient strategy to create structural colors with high color visibility, which is very important for their practical application.

  8. Structure of colloidal sphere-plate mixtures

    Science.gov (United States)

    Doshi, N.; Cinacchi, G.; van Duijneveldt, J. S.; Cosgrove, T.; Prescott, S. W.; Grillo, I.; Phipps, J.; Gittins, D. I.

    2011-05-01

    In addition to containing spherical pigment particles, coatings usually contain plate-like clay particles. It is thought that these improve the opacity of the paint film by providing an efficient spacing of the pigment particles. This observation is counterintuitive, as suspensions of particles of different shapes and sizes tend to phase separate on increase of concentration. In order to clarify this matter a model colloidal system is studied here, with a sphere-plate diameter ratio similar to that found in paints. For dilute suspensions, small angle neutron scattering revealed that the addition of plates leads to enhanced density fluctuations of the spheres, in agreement with new theoretical predictions. On increasing the total colloid concentration the plates and spheres phase separate due to the disparity in their shape. This is in agreement with previous theoretical and experimental work on colloidal sphere-plate mixtures, where one particle acts as a depleting agent. The fact that no large scale phase separation is observed in coatings is ascribed to dynamic arrest in intimately mixed, or possibly micro-phase separated structures, at elevated concentration.

  9. Structure of colloidal sphere-plate mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Doshi, N; Cinacchi, G; Van Duijneveldt, J S; Cosgrove, T; Prescott, S W [School of Chemistry, University of Bristol, Bristol BS8 1TS (United Kingdom); Grillo, I [Institut Laue-Langevin, 6 rue Jules Horowitz BP 156, 38042 Grenoble Cedex 9 (France); Phipps, J [Imerys Minerals Ltd, Par Moor Centre, Par Moor Road, Par, Cornwall PL24 2SQ (United Kingdom); Gittins, D I, E-mail: Giorgio.Cinacchi@bristol.ac.uk, E-mail: J.S.van-Duijneveldt@bristol.ac.uk [Imerys Performance and Filtration Minerals Ltd, 130 Castilian Drive, Goleta, CA 93117 (United States)

    2011-05-18

    In addition to containing spherical pigment particles, coatings usually contain plate-like clay particles. It is thought that these improve the opacity of the paint film by providing an efficient spacing of the pigment particles. This observation is counterintuitive, as suspensions of particles of different shapes and sizes tend to phase separate on increase of concentration. In order to clarify this matter a model colloidal system is studied here, with a sphere-plate diameter ratio similar to that found in paints. For dilute suspensions, small angle neutron scattering revealed that the addition of plates leads to enhanced density fluctuations of the spheres, in agreement with new theoretical predictions. On increasing the total colloid concentration the plates and spheres phase separate due to the disparity in their shape. This is in agreement with previous theoretical and experimental work on colloidal sphere-plate mixtures, where one particle acts as a depleting agent. The fact that no large scale phase separation is observed in coatings is ascribed to dynamic arrest in intimately mixed, or possibly micro-phase separated structures, at elevated concentration.

  10. Structure of crystals of hard colloidal spheres

    Energy Technology Data Exchange (ETDEWEB)

    Pusey, P.N.; van Megen, W.; Bartlett, P.; Ackerson, B.J.; Rarity, J.G.; Underwood, S.M. (Royal Signals and Radar Establishment, Malvern, WR14 3PS, United Kingsom (GB) Department of Applied Physics, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia School of Chemistry, Bristol University, Bristol, BS8 1TS, United Kingdom Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078)

    1989-12-18

    We report light-scattering measurements of powder diffraction patterns of crystals of essentially hard colloidal spheres. These are consistent with structures formed by stacking close-packed planes of particles in a sequence of permitted lateral positions, {ital A},{ital B},{ital C}, which shows a high degree of randomness. Crystals grown slowly, while still containing many stacking faults, show a tendency towards face-centered-cubic packing: possible explanations for this observation are discussed.

  11. Directed Assembly of colloidal rods, spheres and their mixtures

    NARCIS (Netherlands)

    Bakker, H.E.

    2017-01-01

    The directed assembly of colloidal rods, spheres and their mixtures in external fields such as gravity, electric fields and shear flow was investigated. Using confocal microscopy we determined the experimental phase diagram of a binary mixture of colloidal silica rods and spheres that form a binary

  12. Direct measurement of thermodynamic properties of colloidal hard spheres

    NARCIS (Netherlands)

    Dullens, R.P.A.; Kegel, W.K.; Aarts, D.G.A.L.

    2008-01-01

    Recently, we have shown how to measure thermodynamic properties of colloidal hard sphere suspensions by microscopy [Dullens et al. (2006) PNAS 103, 529]. Here, we give full experimental details on how to acquire three dimensional snapshots of a colloidal hard sphere suspension over a wide range of d

  13. A Convenient and Templated Method for the Fabrication of Monodisperse Micrometer Hollow Titania Spheres

    Directory of Open Access Journals (Sweden)

    Haibo Yao

    2013-01-01

    Full Text Available A simple and widely applicable methodology was presented to synthesize monodisperse micrometer hollow titania spheres (HTS based on the templating method. It was performed by using the preformed poly(styrene-acrylic acid (PSA as template spheres which was mixed with tetrabutyltitanate (TBOT in an ethanol solvent under steam treatment. The HTS which were obtained by the calcination of PSA/TiO2 composite core-shell spheres had a narrow particle size distribution and commendable surface topography characterized by SEM. The calcined HTS at 500°C displayed crystalline reflection peaks that were characteristic to the anatase phase by XRD. Moreover, some key influencing factors including TBOT concentration and reaction time were analyzed. As expected, the diameter of HTS could be readily controlled by altering the size of PSA template spheres. In addition, the approach was also applied to fabricate hollow zirconia spheres and other inorganic spheres.

  14. Solvothermal synthesis and controlled self-assembly of monodisperse titanium-based perovskite colloidal nanocrystals

    Science.gov (United States)

    Caruntu, Daniela; Rostamzadeh, Taha; Costanzo, Tommaso; Salemizadeh Parizi, Saman; Caruntu, Gabriel

    2015-07-01

    The rational design of monodisperse ferroelectric nanocrystals with controlled size and shape and their organization into hierarchical structures has been a critical step for understanding the polar ordering in nanoscale ferroelectrics, as well as the design of nanocrystal-based functional materials which harness the properties of individual nanoparticles and the collective interactions between them. We report here on the synthesis and self-assembly of aggregate-free, single-crystalline titanium-based perovskite nanoparticles with controlled morphology and surface composition by using a simple, easily scalable and highly versatile colloidal route. Single-crystalline, non-aggregated BaTiO3 colloidal nanocrystals, used as a model system, have been prepared under solvothermal conditions at temperatures as low as 180 °C. The shape of the nanocrystals was tuned from spheroidal to cubic upon changing the polarity of the solvent, whereas their size was varied from 16 to 30 nm for spheres and 5 to 78 nm for cubes by changing the concentration of the precursors and the reaction time, respectively. The hydrophobic, oleic acid-passivated nanoparticles exhibit very good solubility in non-polar solvents and can be rendered dispersible in polar solvents by a simple process involving the oxidative cleavage of the double bond upon treating the nanopowders with the Lemieux-von Rudloff reagent. Lattice dynamic analysis indicated that regardless of their size, BaTiO3 nanocrystals present local disorder within the perovskite unit cell, associated with the existence of polar ordering. We also demonstrate for the first time that, in addition to being used for fabricating large area, crack-free, highly uniform films, BaTiO3 nanocubes can serve as building blocks for the design of 2D and 3D mesoscale structures, such as superlattices and superparticles. Interestingly, the type of superlattice structure (simple cubic or face centered cubic) appears to be determined by the type of solvent

  15. Synthesis of Monodisperse Walnut-Like SnO2 Spheres and Their Photocatalytic Performances

    Directory of Open Access Journals (Sweden)

    Jing Wang

    2015-01-01

    Full Text Available Novel walnut-like SnO2 spheres have been synthesized using a one-step hydrothermal reaction with SnCl2·2H2O and KOH as raw materials. The morphology, microstructure, and optical properties of the products were characterized by X-ray powder diffraction (XRD, Raman spectrum, scanning electron microscopy (SEM, transmission electron microscopy (TEM, selected area electron diffraction (SAED, and ultraviolet-visible (UV-Vis absorption spectroscopy. The detailed studies revealed that these synthesized spheres are highly monodisperse and have a uniform size of approximately 250 nm. Photocatalytic activity of the prepared SnO2 spheres was evaluated by the degradation of methylene orange. The synthesized SnO2 spheres exhibited excellent photocatalytic degradation. In addition, a possible formation mechanism of the walnut-like nanostructures was proposed based on reaction time-dependent experiments.

  16. Monodisperse Clusters in Charged Attractive Colloids: Linear Renormalization of Repulsion.

    Science.gov (United States)

    Růžička, Štěpán; Allen, Michael P

    2015-08-11

    Experiments done on polydisperse particles of cadmium selenide have recently shown that the particles form spherical isolated clusters with low polydispersity of cluster size. The computer simulation model of Xia et al. ( Nat. Nanotechnol. 2011 , 6 , 580 ) explaining this behavior used a short-range van der Waals attraction combined with a variable long-range screened electrostatic repulsion, depending linearly on the volume of the clusters. In this work, we term this dependence "linear renormalization" of the repulsive term, and we use advanced Monte Carlo simulations to investigate the kinetically slowed down phase separation in a similar but simpler model. We show that amorphous drops do not dissolve and crystallinity evolves very slowly under linear renormalization, and we confirm that low polydispersity of cluster size can also be achieved using this model. The results indicate that the linear renormalization generally leads to monodisperse clusters.

  17. Slip and flow of hard-sphere colloidal glasses.

    Science.gov (United States)

    Ballesta, P; Besseling, R; Isa, L; Petekidis, G; Poon, W C K

    2008-12-19

    We study the flow of concentrated hard-sphere colloidal suspensions along smooth, nonstick walls using cone-plate rheometry and simultaneous confocal microscopy. In the glass regime, the global flow shows a transition from Herschel-Bulkley behavior at large shear rate to a characteristic Bingham slip response at small rates, absent for ergodic colloidal fluids. Imaging reveals both the "solid" microstructure during full slip and the local nature of the "slip to shear" transition. Both the local and global flow are described by a phenomenological model, and the associated Bingham slip parameters exhibit characteristic scaling with size and concentration of the hard spheres.

  18. Growth Kinetics of Monodisperse Polystyrene Microspheres Prepared by Dispersion Polymerization

    Directory of Open Access Journals (Sweden)

    Fan Li

    2013-01-01

    Full Text Available Dispersion polymerization has been widely applied to the synthesis of monodisperse micron-sized polymer colloidal spheres. Many efforts have been devoted to studying the influence of initial conditions on the size and uniformity of the resultant microspheres, aiming to synthesize micron-size monodisperse colloidal spheres. However, the inner contradiction between the size and the size distribution of colloidal spheres hinders the realization of this goal. In this work, we drew our attention from the initial conditions to the growth stage of dispersion polymerization. We tracked the size evolution of colloidal sphere during the dispersion polymerization, through which we established a kinetic model that described the relationship between the monomer concentration and the reaction time. The model may provide a guideline to prepare large polymer colloidal spheres with good monodispersity by continuous monomer feeding during the growth stage to maintain the concentration of monomer at a constant value in a dispersion polymerization process.

  19. Effective Depletion Potential of Colloidal Spheres

    Institute of Scientific and Technical Information of China (English)

    LI Wei-Hua; MA Hong-Ru

    2004-01-01

    @@ A new semianalytical method, which is a combination of the density functional theory with Rosenfeld density functional and the Ornstein-Zernike equation, is proposed for the calculation of the effective depletion potentials between a pair of big spheres immersed in a small hard sphere fluid. The calculated results are almost identical to the integral equation method with the Percus-Yevick approximation, and are also in agreement well with the Monte Carlo simulation results.

  20. Dynamics of polyelectrolyte adsorption and colloidal flocculation upon mixing studied using mono-dispersed polystyrene latex particles

    NARCIS (Netherlands)

    Feng, Lili; Cohen Stuart, Martien; Adachi, Yasuhisa

    2015-01-01

    The dynamic behavior of polyelectrolytes just after their encounter with the surface of bare colloidal particles is analyzed, using the flocculation properties of mono-dispersed polystyrene latex (PSL) particles. Applying a Standardized Colloid Mixing (SCM) approach, effects of ionic strength and

  1. Molecularly imprinted shells from polymer and xerogel matrices on polystyrene colloidal spheres.

    Science.gov (United States)

    Guan, Guijian; Liu, Renyong; Mei, Qingsong; Zhang, Zhongping

    2012-04-10

    We have devised a facile and general methodology for the synthesis of various molecularly imprinted shells at the surface of polystyrene (PS) colloidal spheres to recognize the explosive compound 2,4,6-trinitrotoluene (TNT). PS spheres with surface-functionalized carboxyl-group layers could direct a selective imprinting polymerization on their surface through the hydrogen-bonding interactions between surface carboxyl groups and amino monomers. Meanwhile, homogeneous polymerization in the solution phase was completely prevented by stepwise polymerization. The overall process led to the formation of monodisperse molecularly imprinted core-shell microspheres, and was very successful in the preparation of organic polymer and inorganic xerogel shells. Furthermore, greater capacity and faster binding kinetics towards target species were achieved, because surface-imprinted sites ensured the complete removal of templates, good accessibility to target molecules, and low mass-transfer resistance. The results reported herein, concerning the production of high-quality molecularly imprinted products, could also form the basis for the formulation of a new strategy for the fabrication of various functional coating layers on colloidal spheres with potential applications in the fields of separations and chemical sensing.

  2. Self-assembly in colloidal hard-sphere systems

    NARCIS (Netherlands)

    Filion, L.C.

    2011-01-01

    In this thesis, we examine the phase behaviour and nucleation in a variety of hard-sphere systems. In Chapter 1 we present a short introduction and describe some of the simulation techniques used in this thesis. One of the main difficulties in predicting the phase behaviour in colloidal, atomic and

  3. Self-assembly in colloidal hard-sphere systems

    NARCIS (Netherlands)

    Filion, L.C.|info:eu-repo/dai/nl/326823484

    2011-01-01

    In this thesis, we examine the phase behaviour and nucleation in a variety of hard-sphere systems. In Chapter 1 we present a short introduction and describe some of the simulation techniques used in this thesis. One of the main difficulties in predicting the phase behaviour in colloidal, atomic and

  4. Effect of colloidal particle size on adsorbed monodisperse and bidisperse monolayers.

    Science.gov (United States)

    Rosenberg, Rachel T; Dan, Nily

    2011-07-19

    Coating hydrogel films or microspheres by an adsorbed colloidal shell is one synthesis method for forming colloidosomes. The colloidal shell allows control of the release rate of encapsulated materials, as well as selective transport. Previous studies found that the packing density of self-assembled, adsorbed colloidal monolayers is independent of the colloidal particle size. In this paper we develop an equilibrium model that correlates the packing density of charged colloidal particles in an adsorbed shell to the particle dimensions in monodisperse and bidisperse systems. In systems where the molar concentration in solution is fixed, the increase in adsorption energy with increasing particle size leads to a monotonic increase in the monolayer packing density with particle radius. However, in systems where the mass fraction of the particles in the adsorbing solutions is fixed, increasing particle size also reduces the molar concentration of particles in solution, thereby reducing the probability of adsorption. The result is a nonmonotonic dependence of the packing density in the adsorbed layer on the particle radius. In bidisperse monolayers composed of two particle sizes, the packing density in the layer increases significantly with size asymmetry. These results may be utilized to design the properties of colloidal shells and coatings to achieve specific properties such as transport rate and selectivity.

  5. A SURFACTANT-ASSISTED APPROACH FOR PREPARING COLLOIDAL AZO POLYMER SPHERES WITH NARROW SIZE DISTRIBUTION

    Institute of Scientific and Technical Information of China (English)

    Xiao-lan Tong; Yao-bang Li; Ya-ning He; Xiao-gong Wang

    2006-01-01

    A surfactant-assisted method for preparing colloidal spheres with narrow size distribution from a polydispersed azo polymer has been developed in this work. The colloidal spheres were formed through gradual hydrophobic aggregation of the polymeric chains in THF-H2O dispersion media, which was induced by a steady increase in the water content. Results showed that the addition of a small amount of surfactant (SDBS) could significantly narrow the size distribution of the colloidal spheres. The size distribution of the colloidal spheres was determined by the concentrations of azo polymer and the amount of surfactant in the systems. When the concentrations of polymer and surfactant amount were in a proper range,colloidal spheres with narrow size distribution could be obtained. The colloidal spheres formed by this method could be elongated along the polarization direction of the laser beams upon Ar+ laser irradiation. The colloidal spheres are considered to be a new type of the colloid-based functional materials.

  6. When mixtures of hard-sphere-like colloids do not behave as mixtures of hard spheres.

    Science.gov (United States)

    Germain, Ph; Malherbe, J G; Amokrane, S

    2004-10-01

    The validity of the concept of "hard-sphere-like" particles for mixtures of colloids is questioned from a theoretical point of view. This concerns the class of pseudobinary mixtures in which the nonsteric interactions between the colloids are "residual" (with very small range and moderate strength). It is shown that contrary to common expectation, such interactions may have unexpected consequences on the theoretical phase diagram. The distinction between this situation and true solute-solvent mixtures is emphasized.

  7. Structure-transport correlation for the diffusive tortuosity of bulk, monodisperse, random sphere packings.

    Science.gov (United States)

    Khirevich, Siarhei; Höltzel, Alexandra; Daneyko, Anton; Seidel-Morgenstern, Andreas; Tallarek, Ulrich

    2011-09-16

    The mass transport properties of bulk random sphere packings depend primarily on the bed (external) porosity ε, but also on the packing microstructure. We investigate the influence of the packing microstructure on the diffusive tortuosity τ=D(m)/D(eff), which relates the bulk diffusion coefficient (D(m)) to the effective (asymptotic) diffusion coefficient in a porous medium (D(eff)), by numerical simulations of diffusion in a set of computer-generated, monodisperse, hard-sphere packings. Variation of packing generation algorithm and protocol yielded four Jodrey-Tory and two Monte Carlo packing types with systematically varied degrees of microstructural heterogeneity in the range between the random-close and the random-loose packing limit (ε=0.366-0.46). The distinctive tortuosity-porosity scaling of the packing types is influenced by the extent to which the structural environment of individual pores varies in a packing, and to quantify this influence we propose a measure based on Delaunay tessellation. We demonstrate that the ratio of the minimum to the maximum void face area of a Delaunay tetrahedron around a pore between four adjacent spheres, (A(min)/A(max))(D), is a measure for the structural heterogeneity in the direct environment of this pore, and that the standard deviation σ of the (A(min)/A(max))(D)-distribution considering all pores in a packing mimics the tortuosity-porosity scaling of the generated packing types. Thus, σ(A(min)/A(max))(D) provides a structure-transport correlation for diffusion in bulk, monodisperse, random sphere packings. Copyright © 2011 Elsevier B.V. All rights reserved.

  8. Microwave Synthesized Monodisperse CdS Spheres of Different Size and Color for Solar Cell Applications

    Directory of Open Access Journals (Sweden)

    Carlos A. Rodríguez-Castañeda

    2015-01-01

    Full Text Available Monodisperse CdS spheres of size of 40 to 140 nm were obtained by microwave heating from basic solutions. It is observed that larger CdS spheres were formed at lower solution pH (8.4–8.8 and smaller ones at higher solution pH (10.8–11.3. The color of CdS products changed with solution pH and reaction temperature; those synthesized at lower pH and temperature were of green-yellow color, whereas those formed at higher pH and temperature were of orange-yellow color. A good photovoltage was observed in CdS:poly(3-hexylthiophene solar cells with spherical CdS particles. This is due to the good dispersion of CdS nanoparticles in P3HT solution that led to a large interface area between the organic and inorganic semiconductors. Higher photocurrent density was obtained in green-yellow CdS particles of lower defect density. The efficient microwave chemistry accelerated the hydrolysis of thiourea in pH lower than 9 and produced monodisperse spherical CdS nanoparticles suitable for solar cell applications.

  9. Random-close packing limits for monodisperse and polydisperse hard spheres.

    Science.gov (United States)

    Baranau, Vasili; Tallarek, Ulrich

    2014-06-07

    We investigate how the densities of inherent structures, which we refer to as the closest jammed configurations, are distributed for packings of 10(4) frictionless hard spheres. A computational algorithm is introduced to generate closest jammed configurations and determine corresponding densities. Closest jamming densities for monodisperse packings generated with high compression rates using Lubachevsky-Stillinger and force-biased algorithms are distributed in a narrow density range from φ = 0.634-0.636 to φ≈ 0.64; closest jamming densities for monodisperse packings generated with low compression rates converge to φ≈ 0.65 and grow rapidly when crystallization starts with very low compression rates. We interpret φ≈ 0.64 as the random-close packing (RCP) limit and φ≈ 0.65 as a lower bound of the glass close packing (GCP) limit, whereas φ = 0.634-0.636 is attributed to another characteristic (lowest typical, LT) density φLT. The three characteristic densities φLT, φRCP, and φGCP are determined for polydisperse packings with log-normal sphere radii distributions.

  10. Mono-dispersed cross-linked polystyrene micro-spheres prepared by seed swelling polymerization method

    Institute of Scientific and Technical Information of China (English)

    Dongsha WANG; Yanjun LIU

    2008-01-01

    A two-step swelling procedure was adopted to synthesize mono-dispersed and highly cross-linked poly (St-divinylbenzene) particles with PSt micro-spheres (1.80 μmin diameter). The PSt micro-spheres were prepared by a dispersion polymerization method and used as seeds. The effects of monomer concentration, ratio of ethanol to water, swelling reagents, crosslinking reagents, swelling temper-ature and agitation speed on particle size were investigated in detail. The morphologies and size distributions of these micro-spheres were examined by SEM and particle size analysis (PSA). The Tg of the micro-spheres was measured by DSC. The results indicate that the particles (6.20 μm in diameter) exhibit excellent mono dispersed property and high crosslinking degree when the concentration of the swelling reagent was 25%, the concentration of the cross-linking reagents was 23%, the swelling temperature was 30℃ and the stirring speed was 150 r/min.

  11. Passive and active microrheology of hard-sphere colloids.

    Science.gov (United States)

    Wilson, L G; Harrison, A W; Schofield, A B; Arlt, J; Poon, W C K

    2009-03-26

    We performed passive and active microrheology using probe particles in a bath of well-characterized, model hard-sphere colloids in the fluid state over the whole range of volume fractions below the glass transition. The probe and bath particles have nearly the same size. Passive tracking of probe particles yields short-time self-diffusion coefficients. Comparison with literature data demonstrates that the interaction between probe and bath particles is hard-sphere-like. The short-time diffusivities yield one set of microviscosities as a function of volume fraction, which agrees with previous macrorheological measurements of the high-frequency viscosity of hard-sphere colloids. Using optical tweezers, we measure the force on a trapped probe particle as the rest of the sample is translated at constant velocity. This yields a second set of microviscosities at high Péclet numbers. These agree with previous macrorheological measurements of the high-shear viscosity of similar colloids, at shear-rates below the onset of shear-thickening.

  12. Phase diagrams of colloidal spheres with a constant zeta-potential

    NARCIS (Netherlands)

    Smallenburg, F.|info:eu-repo/dai/nl/313939039; Boon, N.J.H.|info:eu-repo/dai/nl/313960143; Kater, M.; Dijkstra, M.|info:eu-repo/dai/nl/123538807; van Roij, R.H.H.G.|info:eu-repo/dai/nl/152978984

    2011-01-01

    We study suspensions of colloidal spheres with a constant zeta-potential within Poisson–Boltzmann theory, quantifying the discharging of the spheres with increasing colloid density and decreasing salt concentration. We use the calculated renormalized charge of the colloids to determine their

  13. Small silicon, big opportunities: the development and future of colloidally-stable monodisperse silicon nanocrystals.

    Science.gov (United States)

    Mastronardi, Melanie L; Henderson, Eric J; Puzzo, Daniel P; Ozin, Geoffrey A

    2012-11-14

    Nanomaterials are becoming increasingly widespread in consumer technologies, but there is global concern about the toxicity of nanomaterials to humans and the environment as they move rapidly from the research laboratory to the market place. With this in mind, it makes sense to intensify the nanochemistry community's global research effort on the synthesis and study of nanoparticles that are purportedly "green". One potentially green nanoparticle that seems to be a most promising candidate in this context is silicon, whose appealing optical, optoelectronic, photonic, and biomedical attributes are recently gaining much attention. In this paper, we outline some of our recent contributions to the development of the growing field of silicon nanocrystals (ncSi) in order to stress the importance of continued study of ncSi as a green alternative to the archetypal semiconductor nanocrystals like CdSe, InAs, and PbS. While a variety of developments in synthetic methods, characterization techniques, and applications have been reported in recent years, the ability to prepare colloidally-stable monodisperse ncSi samples may prove to have the largest impact on the field, as it opens the door to study and access the tunable size-dependent properties of ncSi. Here, we summarize our recent contributions in size-separation methods to achieve monodisperse samples, the characterization of size-dependant property trends, the development of ncSi applications, and their potential impact on the promising future of ncSi.

  14. Depletion potentials in colloidal mixtures of hard spheres and rods.

    Science.gov (United States)

    Li, Weihua; Yang, Tao; Ma, Hong-ru

    2008-01-28

    The depletion potential between a hard sphere and a planar hard wall, or two hard spheres, imposed by suspended rigid spherocylindrical rods is computed by the acceptance ratio method through the application of Monte Carlo simulation. The accurate results and ideal-gas approximation results of the depletion potential are determined with the acceptance ratio method in our simulations. For comparison, the depletion potentials are also studied by using both the density functional theory and Derjaguin approximations. The density profile as a function of positions and orientations of rods, used in the density functional theory, is calculated by Monte Carlo simulation. The potential obtained by the acceptance ratio method is in good agreement with that of density functional theory under the ideal-gas approximation. The comparison between our results and those of other theories suggests that the acceptance ratio method is the only efficient method used to compute the depletion potential induced by nonspherical colloids with the volume fraction beyond the ideal-gas approximation.

  15. Sedimentation of concentrated monodisperse colloidal suspensions: role of collective particle interaction forces.

    Science.gov (United States)

    Vesaratchanon, Jan S; Nikolov, Alex; Wasan, Darsh T

    2008-06-01

    The sedimentation velocities and concentration profiles of low-charge, monodisperse hydroxylate latex particle suspensions were investigated experimentally as a function of the particle concentration to study the effects of the collective particle interactions on suspension stability. We used the Kossel diffraction technique to measure the particle concentration profile and sedimentation rate. We conducted the sedimentation experiments using three different particle sizes. Collective hydrodynamic interactions dominate the particle-particle interactions at particle concentrations up to 6.5 vol%. However, at higher particle concentrations, additional collective particle-particle interactions resulting from the self-depletion attraction cause particle aggregation inside the suspension. The collective particle-particle interaction forces play a much more important role when relatively small particles (500 nm in diameter or less) are used. We developed a theoretical model based on the statistical particle dynamics simulation method to examine the role of the collective particle interactions in concentrated suspensions in the colloidal microstructure formation and sedimentation rates. The theoretical results agree with the experimentally-measured values of the settling velocities and concentration profiles.

  16. Facile synthesis and characterization of uniform CdS colloidal spheres

    Institute of Scientific and Technical Information of China (English)

    Xiu Jie Yang; Xin Ping Li; Xiang Tao Bai; Li Qiang Zheng

    2012-01-01

    Uniform CdS colloidal spheres have been successfully synthesized via a simple hydrothermal method.X-ray diffraction (XRD) analyses indicate that the products exhibit a hexagonal structure.Scanning electron (SEM) and transmission electron microscopy (TEM) are used to characterize CdS colloidal spheres.The final size of the spheres may be selected from a range of 71 ± 2 nm to approximately 181 ± 5 nm by changing the amount of polyvinylpyrrolidone (PVP) and hexamethylenetetramine (HMT).The CdS colloidal spheres are not obtained in the absence of either of the capping agents.A synergistic effect between HMT and PVP is proposed to be crucial for the formation of colloidal spheres.

  17. Preparation of modified SiO2 colloidal spheres with succinic acid and the assembly of colloidal crystals

    Institute of Scientific and Technical Information of China (English)

    FANG Jun; WANG XiuFeng; WANG LieSong; CHENG Bing; WU YuanTing; ZHU WanLin

    2007-01-01

    SiO2 colloidal spheres were synthesized by St(o)ber method. In order to enhance surface charge of the SiO2 spheres, they were modified with succinic acid. Scanning electron microscope (SEM) shows that the average size of modified SiO2 spheres is 473 nm, and its distribution standard deviation is less than 5%; Fourier-transform infrared spectra (FT-IR) and X-ray photoelectron spectrometer (XPS) results indicate that one end of succinic acid is chemically bonded to the SiO2 spheres through esterification; Zeta potential of the modified SiO2 spheres in water solution is improved from -53.72 to -67.46 mV, and surface charge density of the modified SiO2 spheres is enhanced from 0.19 to 0.94 μC/cm2. SiO2 colloidal crystal was fabricated from aqueous colloidal solution by the vertical deposition method at 40℃ and 60% relative humidity. SEM images show that the sample of SiO2 colloidal crystal is face-centered cubic (fcc) structure with its (111) planes parallel to the substrate. Transmission measurement shows the existence of photonic band gap at 1047 nm.

  18. Synthesis, photocatalytic activity, and photogenerated hydroxyl radicals of monodisperse colloidal ZnO nanospheres

    Science.gov (United States)

    Yang, Chong; Li, Qingsong; Tang, Limei; Xin, Kun; Bai, Ailing; Yu, Yingmin

    2015-12-01

    In the present study, monodisperse colloidal zinc oxide (ZnO) nanospheres were successfully synthesized via a newly developed two-stage solution method followed by facile calcination at various temperatures. The effects of calcination temperature on the structure, morphology, and optical properties as well as the photocatalytic activity of the as-made ZnO samples were investigated systematically by Fourier transform infrared spectrometry, X-ray diffraction, field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, diffuse reflectance UV-visible spectroscopy (DRS), photoluminescence, and related photocatalytic activity tests. The thermal decomposition was analyzed by thermogravimetric analysis. The crystallinity was found to gradually increase with increasing calcination temperature, whereas the decrease in the Brunauer-Emmett-Teller specific surface area of the samples with calcination may be ascribed to the increased particle size. The DRS results provided clear evidence for the decrease in band gap energy of ZnO samples with an increase in calcination temperature. The photoluminescence spectra demonstrated the calcination-dependent emission features, especially the UV emission intensity. In particular, the ZnO product calcined at 400 °C exhibited the highest photocatalytic activity, degrading methylene blue by almost 99.1% in 70 min, which is ascribed to the large specific surface area and pore volume, high electron-hole pair separation efficient, and great redox potential of the obtained ZnO nanoparticles. In addition, the production of photogenerated hydroxyl radicals (•OH) was consistent with the methylene blue degradation efficiency over the as-made ZnO nanoparticles. Using isopropanol as a hydroxyl radical scavenger, •OH was determined to be the main active oxygen species in the photocatalytic process. A possible mechanism of photodegradation under UV light irradiation also is proposed.

  19. Antisolvent Precipitation for the Synthesis of Monodisperse Mesoporous Niobium Oxide Spheres as Highly Effective Solid Acid Catalysts

    KAUST Repository

    Li, Cheng Chao

    2012-03-20

    We have developed a low-cost reaction protocol to synthesize mesoporous Nb 2O 5-based solid acid catalysts with external shape control. In the synthesis, monodisperse glycolated niobium oxide spheres (GNOS) were prepared by means of a simple antisolvent precipitation approach and subsequently converted to mesoporous niobium oxide spheres (MNOS) with a large surface area of 312m 2g -1 by means of the hydrothermal treatment. The antisolvent acetone used to obtain GNOS was recovered through distillation at high purity. The obtained mesoporous MNOS were functionalized further with sulfate anions at different temperatures or incorporated with tungstophosphoric acid to obtain recyclable solid acid catalysts. These MNOS-based catalysts showed excellent performance in a wide range of acid-catalyzed reactions, such as Friedel-Crafts alkylation, esterification, and hydrolysis of acetates. As they are monodisperse spheres with diameters in the submicrometer range, the catalysts can be easily separated and reused. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Oscillatory-shear-induced order in nonaqueous dispersions of charged colloidal spheres

    NARCIS (Netherlands)

    Yan, Y.D.; Dhont, J.K.G.; Smits, C.; Lekkerkerker, H.N.W.

    1994-01-01

    A light scattering study is presented of the nonequilibrium microstructure of nonaqueous dispersions of repulsive charged colloidal silica spheres subjected to an oscillatory shear flow. Two ordered structures are induced upon increasing the oscillation amplitude: alternating face-centred-cubic

  1. Phase diagrams of colloidal spheres with a constant zeta-potential.

    Science.gov (United States)

    Smallenburg, Frank; Boon, Niels; Kater, Maarten; Dijkstra, Marjolein; van Roij, René

    2011-02-21

    We study suspensions of colloidal spheres with a constant zeta-potential within Poisson-Boltzmann theory, quantifying the discharging of the spheres with increasing colloid density and decreasing salt concentration. We use the calculated renormalized charge of the colloids to determine their pairwise effective screened-Coulomb repulsions. Bulk phase diagrams in the colloid concentration-salt concentration representation follow, for various zeta-potentials, by a mapping onto published fits of phase boundaries of point-Yukawa systems. Although the resulting phase diagrams do feature face-centered cubic and body-centered cubic phases, they are dominated by the (re-entrant) fluid phase due to the colloidal discharging with increasing colloid concentration and decreasing salt concentration.

  2. 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.

  3. Bulk and wetting phenomena in a colloidal mixture of hard spheres and platelets

    OpenAIRE

    Harnau, L.; Dietrich, S.

    2004-01-01

    Density functional theory is used to study binary colloidal fluids consisting of hard spheres and thin platelets in their bulk and near a planar hard wall. This system exhibits liquid-liquid coexistence of a phase that is rich in spheres (poor in platelets) and a phase that is poor in spheres (rich in platelets). For the mixture near a planar hard wall, we find that the phase rich in spheres wets the wall completely upon approaching the liquid demixing binodal from the sphere-poor phase, prov...

  4. Hybrid thin films derived from UV-curable acrylate-modified waterborne polyurethane and monodispersed colloidal silica

    Directory of Open Access Journals (Sweden)

    C. H. Yang

    2012-01-01

    Full Text Available Hybrid thin films containing nano-sized inorganic domains were synthesized from UV-curable acrylate-modified waterborne polyurethane (WPU-AC and monodispersed colloidal silica with coupling agent. The coupling agent, 3-(trimethoxysilylpropyl methacrylate (MSMA, was bonded onto colloidal silica first, and then mixed with WPU-AC to form a precursor solution. This precursor was spin coated, dried and UV-cured to generate the hybrid films. The silica content in the hybrid thin films was varied from 0 to 30 wt%. Experimental results showed the aggregation of silica particles in the hybrid films. Thus, the silica domain in the hybrid films was varied from 30 to 50 nm by the different ratios of MSMAsilica to WPU-AC. The prepared hybrid films from the crosslinked WPU-AC/MSMA-silica showed much better thermal stability and mechanical properties than pure WPU-AC.

  5. Packing Effect of Excluded Volume on Hard-Sphere Colloids

    Institute of Scientific and Technical Information of China (English)

    肖长明; 金国钧; 马余强

    2001-01-01

    We apply the principle of maximum entropy to consider the excluded volume effect on the phase separation of binary mixtures consisting of hard spheres with two different diameters. We show that a critical volume fraction of hard spheres exists locating the packing of large spheres. In particular, through numerical calculation, we have found that the critical volume fraction becomes lower when the ratio α = σ1/σ2 of large-to-small sphere diameters increases, but becomes higher when the ratio of the large sphere volume fraction to the total volume fraction of large and small spheres increases.

  6. Fabrication of monodisperse hollow silica spheres and effect on water vapor permeability of polyacrylate membrane.

    Science.gov (United States)

    Bao, Yan; Yang, Yongqiang; Ma, Jianzhong

    2013-10-01

    Polystyrene/silica core-shell spheres were fabricated using polystyrene as templates by hydrolysis and condensation of tetraethyl orthosilicate through a sol-gel process, in which polystyrene was synthesized by emulsion polymerization. Then, hollow silica spheres were obtained after selective removal of the organic polystyrene core from the polystyrene/silica core-shell spheres by tetrahydrofuran etching. The effect of hollow silica spheres on water vapor permeability, mechanical property, and water uptake of polyacrylate membrane were investigated. The microstructure analysis shows that the mean size and wall thickness of hollow silica spheres are 170 nm and 20 nm, respectively. The silica shells consist of amorphous silica seed assembly with a broad size distribution, which roughen the surfaces of hollow silica spheres greatly. The specific surface area of hollow silica spheres is bigger than that of polystyrene/silica core-shell spheres. Hollow silica spheres can significantly improve water vapor permeability of polyacrylate membrane, but lead to the reduction in mechanical property.

  7. Fabrication of Phase-Change Polymer Colloidal Photonic Crystals

    Directory of Open Access Journals (Sweden)

    Tianyi Zhao

    2014-01-01

    Full Text Available This paper presents the preparation of phase-change polymer colloidal photonic crystals (PCs by assembling hollow latex spheres encapsulated with dodecanol for the first time. The monodispersed hollow latex spheres were obtained by phase reversion of monodispersed core-shell latex spheres in the n-hexane, which dissolves the PS core and retains the PMMA/PAA shell. The as-prepared phase-change colloidal PCs show stable phase-change behavior. This fabrication of phase-change colloidal PCs would be significant for PC’s applications in functional coatings and various optic devices.

  8. Numerical simulations of flows through fixed networks of monodispersed and bi-dispersed spheres, for moderate Reynolds numbers; Simulations numeriques d'ecoulements a travers des reseaux fixes de spheres monodisperses et bidisperses, pour des nombres de Reynolds moderes

    Energy Technology Data Exchange (ETDEWEB)

    Massol, A.

    2004-02-15

    The application of statistically averaged two-fluid models for the simulation of complex indus- trial two-phase flows requires the development of adequate models for the drag force exerted on the inclusions and the interfacial heat exchange. This task becomes problematic at high volume fractions of the dispersed phase. The quality of the simulation strongly depends upon the inter- facial exchange terms, starting with the steady drag force. For example, an accurate modelling of the drag force is therefore a crucial point to simulate the expansion of dense fluidized beds. Most models used to study the exchange terms between particles and fluids are based on the interaction between an isolated particle and a surrounding gas. Those models are clearly not adequate in cases where the volume fraction of particles increases and particle-particle interactions become important. Studying such cases is a complex task because of the multiple possible configurations. While the interaction between an isolated sphere and a gas depends only on the particle size and the slip velocity between gas and particles, the interaction between a cloud of particles and a gas depends on many more parameters: size and velocity distribution of particles, relative position of particles. Even if the particles keep relative fixed positions, there is an infinite number of combinations to construct such an array. The objective of the present work is to perform steady and unsteady simulations of the flow in regular arrays of fixed particles in order to analyze the influence of the size and distributions of spheres on drag force and heat transfer (the array of spheres can be either monodispersed, either bi-dispersed). Several authors have studied the drag exerted on the spheres, but only for low Reynolds numbers and/or solid volume fractions close to the packed limit. Moreover some discrepancies are observed between the different studies. On top of that, all existing studies are limited to steady flows

  9. Solidification of a colloidal hard sphere like model system approaching and crossing the glass transition.

    Science.gov (United States)

    Franke, Markus; Golde, Sebastian; Schöpe, Hans Joachim

    2014-08-07

    We investigated the process of vitrification and crystallization in a model system of colloidal hard spheres. The kinetics of the solidification process was measured using time resolved static light scattering, while the time evolution of the dynamic properties was determined using time resolved dynamic light scattering. By performing further analysis we confirm that solidification of hard sphere colloids is mediated by precursors. Analyzing the dynamic properties we can show that the long time dynamics and thus the shear rigidity of the metastable melt is highly correlated with the number density of solid clusters (precursors) nucleated. In crystallization these objects convert into highly ordered crystals whereas in the case of vitrification this conversion is blocked and the system is (temporarily) locked in the metastable precursor state. From the early stages of solidification one cannot clearly conclude whether the melt will crystallize or vitrify. Furthermore our data suggests that colloidal hard sphere glasses can crystallize via homogeneous nucleation.

  10. Monodisperse TiO2 Spheres with High Charge Density and Their Self-Assembly.

    Science.gov (United States)

    Xia, Hongbo; Wu, Suli; Su, Xin; Zhang, Shufen

    2017-01-03

    Titanium dioxide (TiO2 ) spheres are potential candidates to fabricate three-dimensional (3D) photonic crystals owing to their high refractive index and low absorption in the visible and near-infrared regions. Here, TiO2 spheres with both high surface charge density and uniform size, which are necessary for the self-assembly of TiO2 spheres, have been prepared by means of sol-gel methods in ethanol in the presence of thioglycolic acid as ligand. Thioglycolic acid, which contains two functional groups, not only acts as coordinating ligand for stabilizing and controlling the growth of TiO2 spheres but also endows the resulting TiO2 spheres with high charge density as based on ζ-potential analysis when the pH of the TiO2 aqueous dispersion was 6.5 or higher. The SEM images illustrate that the diameter of the prepared TiO2 spheres can be tuned from 100 to 300 nm by simply controlling the concentration of H2 O. FTIR spectra confirm that thioglycolic acid bonded to the surface of TiO2 spheres through carboxylic groups. As anticipated, the obtained TiO2 spheres could self-assemble to form a 3D opal photonic crystal structure by means of a simple gravity sedimentation method. Then the TiO2 spheres in the 3D opal photonic crystal structure were able to transform into a pure anatase phase by annealing at different temperatures.

  11. Bulk fluid phase behaviour of colloidal platelet-sphere and platelet-polymer mixtures.

    Science.gov (United States)

    de las Heras, Daniel; Schmidt, Matthias

    2013-04-13

    Using a geometry-based fundamental measure density functional theory, we calculate bulk fluid phase diagrams of colloidal mixtures of vanishingly thin hard circular platelets and hard spheres. We find isotropic-nematic phase separation, with strong broadening of the biphasic region, upon increasing the pressure. In mixtures with large size ratio of platelet and sphere diameters, there is also demixing between two nematic phases with differing platelet concentrations. We formulate a fundamental measure density functional for mixtures of colloidal platelets and freely overlapping spheres, which represent ideal polymers, and use it to obtain phase diagrams. We find that, for low platelet-polymer size ratio, in addition to isotropic-nematic and nematic-nematic phase coexistence, platelet-polymer mixtures also display isotropic-isotropic demixing. By contrast, we do not find isotropic-isotropic demixing in hard-core platelet-sphere mixtures for the size ratios considered.

  12. Bulk and wetting phenomena in a colloidal mixture of hard spheres and platelets.

    Science.gov (United States)

    Harnau, L; Dietrich, S

    2005-01-01

    Density functional theory is used to study binary colloidal fluids consisting of hard spheres and thin platelets in their bulk and near a planar hard wall. This system exhibits liquid-liquid coexistence of a phase that is rich in spheres (poor in platelets) and a phase that is poor in spheres (rich in platelets). For the mixture near a planar hard wall, we find that the phase rich in spheres wets the wall completely upon approaching the liquid demixing binodal from the sphere-poor phase, provided the concentration of the platelets is smaller than a threshold value which marks a first-order wetting transition at coexistence. No layering transitions are found, in contrast to recent studies on binary mixtures of spheres and nonadsorbing polymers or thin hard rods.

  13. Phase behaviour of deionized binary mixtures of charged colloidal spheres.

    Science.gov (United States)

    Lorenz, Nina J; Schöpe, Hans Joachim; Reiber, Holger; Palberg, Thomas; Wette, Patrick; Klassen, Ina; Holland-Moritz, Dirk; Herlach, Dieter; Okubo, Tsuneo

    2009-11-18

    We review recent work on the phase behaviour of binary charged sphere mixtures as a function of particle concentration and composition. Both size ratios Γ and charge ratios Λ are varied over a wide range. Unlike the case for hard spheres, the long-ranged Coulomb interaction stabilizes the crystal phase at low particle concentrations and shifts the occurrence of amorphous solids to particle concentrations considerably larger than the freezing concentration. Depending on Γ and Λ, we observe upper azeotrope, spindle, lower azeotrope and eutectic types of phase diagrams, all known well from metal systems. Most solids are of body centred cubic structure. Occasionally stoichiometric compounds are formed at large particle concentrations. For very low Γ, entropic effects dominate and induce a fluid-fluid phase separation. Since for charged spheres the charge ratio Λ is also decisive for the type of phase diagram, future experiments with charge variable silica spheres are suggested.

  14. Depletion potential in colloidal mixtures of hard spheres and platelets.

    Science.gov (United States)

    Harnau, L; Dietrich, S

    2004-05-01

    The depletion potential between two hard spheres in a solvent of thin hard disclike platelets is investigated by using either the Derjaguin approximation or density functional theory. Particular attention is paid to the density dependence of the depletion potential. A second-order virial approximation is applied, which yields nearly exact results for the bulk properties of the hard-platelet fluid at densities two times smaller than the density of the isotropic fluid at isotropic-nematic phase coexistence. As the platelet density increases, the attractive primary minimum of the depletion potential deepens and an additional small repulsive barrier at larger sphere separations develops. Upon decreasing the ratio of the radius of the spheres and the platelets, the primary minimum diminishes and the position of the small repulsive barrier shifts to smaller values of the sphere separation.

  15. Solid–liquid interfacial free energy of small colloidal hard-sphere crystals

    NARCIS (Netherlands)

    Cacciuto, A.; Auer, S.; Frenkel, D.

    2003-01-01

    Using free-energy calculations on small crystalline clusters, we estimate the free-energy density γSL for the solid–liquid equimolar interface of a system of hard-sphere colloids. By studying the behavior of a crystallite at coexistence, we determine the dependence of γSL on the radius of curvature

  16. Concentrated, polydisperse solutions of colloidal particles. Light scattering and sedimentation of hard-sphere mixture

    NARCIS (Netherlands)

    Vrij, A.

    1982-01-01

    The usefulness of the hard-sphere model in characterizing polydispersity in concentrated colloidal solutions is stressed. A recently derived equation for (∂ρi/∂μj)μ is used to give a simpler route for application to light scattering and sedimentation in multicomponent and polydisperse systems. Some

  17. Direct observation of dynamical heterogeneities in colloidal hard-sphere suspensions

    NARCIS (Netherlands)

    Kegel, W.K.; Blaaderen, A. van

    2000-01-01

    The real-space dynamics in a model system of colloidal hard spheres was studied by means of time-resolved ßuorescence confocal scanning microscopy. Direct experimental evidence for the presence of dynamical heterogeneities in a dense liquid was obtained from an analysis of particle trajectories in t

  18. Tunable long range forces mediated by self-propelled colloidal hard spheres

    NARCIS (Netherlands)

    Ni, R.; Cohen Stuart, M.A.; Bolhuis, P.G.

    2015-01-01

    Using Brownian dynamics simulations, we systematically study the effective interaction between two parallel hard walls in a 2D suspension of self-propelled (active) colloidal hard spheres, and we find that the effective force between two hard walls can be tuned from a long range repulsion into a lon

  19. Fabrication of functional hollow carbon spheres with large hollow interior as active colloidal catalysts

    Institute of Scientific and Technical Information of China (English)

    Qiang Sun; Guanghui Wang; Wencui Li; Xiangqian Zhang; Anhui Lu

    2012-01-01

    In this study,we have established a facile method to synthesize functional hollow carbon spheres with large hollow interior,which can act as active colloidal catalysts.The method includes the following steps:first,hollow polymer spheres with large hollow interior were prepared using sodium oleate as the hollow core generator,and 2,4-dihydroxybenzoic acid and hexamethylene tetramine (HMT) as the polymer precursors under hydrothermal conditions; Fe3+ or Ag+ cations were then introduced into the as-prepared hollow polymer spheres through the carboxyl groups; finally,the hollow polymer spheres can be pseudomorphically converted to hollow carbon spheres during pyrolysis process,meanwhile iron or silver nanoparticles can also be formed in the carbon shell simultaneously.The structures of the obtained functional hollow carbon spheres were characterized by TEM,XRD,and TG.As an example,Ag-doped hollow carbon spheres were used as colloid catalysts which showed high catalytic activity in 4-nitrophenol reduction reaction.

  20. Hyperuniformity of self-assembled soft colloidal spheres

    Science.gov (United States)

    Bretz, Coline

    2015-03-01

    Hyperuniformity characterizes a state of matter for which density fluctuations vanish on large scales. Hyperuniform materials are of technological importance as they exhibit interesting photonic properties. We have shown that such materials can be obtained by assembling spheres into a disordered jammed 2D- packing. To this end, we use a binary mixture of large and small Poly(NIPAM) particles confined between two cover slips. These soft spheres have been chosen for their temperature-sensitive properties. We can locally increase or decrease the volume fraction occupied by the spheres by finely tuning the temperature. By applying various temperature patterns, we are studying the spatial arrangements of the microgels and characterizing their hyperuniform properties through reconstruction and detection algorithms. CNRS-Rhodia-UPenn UMI 3254, Bristol, PA 19007-3624, USA

  1. Crystal thickness and sphere dispersion dependence of the photonic band gap of silica colloidal crystals

    Institute of Scientific and Technical Information of China (English)

    Yongjun He(何拥军); Zhongchao Wei(韦中超); Yongchun Zhong(钟永春); Jianwei Diao(刁建伟); Hezhou Wang(汪河洲)

    2004-01-01

    Experimental results demonstrate that the band gap of colloidal suspension crystal changes with both the thickness of crystal and the dispersity of micro-spheres.As the thickness decreases,a red shift of band gap is observed,and there is a maximum of red shift.The values of the maximum red shifts are dependent on the standard deviations of micro-spheres.The experimental results are consistent with theoretical calculation.As the colloidal suspension crystal is assembled from micro-spheres with a standard deviation of 8.4% in a thick cell,an incident angles independent broadband is observed,which is explained as an amorphous structure.Two amorphous models are discussed.

  2. Assembly of Fe3O4 nanoparticles on SiO2 monodisperse spheres

    Indian Academy of Sciences (India)

    K C Barick; D Bahadur

    2006-11-01

    The assembly of superparamagnetic Fe3O4 nanoparticles on submicroscopic SiO2 spheres have been prepared by an in situ reaction using different molar ratios of Fe3+/Fe2+ (50–200%). It has been observed that morphology of the assembly and properties of these hybrid materials composed of SiO2 as core and Fe3O4 nanoparticles as shell depend on the molar ratio of Fe3+/Fe2+.

  3. 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

  4. Simulating colloids with Baxter's adhesive hard sphere model

    NARCIS (Netherlands)

    Miller, M.A.; Frenkel, D.

    2004-01-01

    The structure of the Baxter adhesive hard sphere fluid is examined using computer simulation. The radial distribution function (which exhibits unusual discontinuities due to the particle adhesion) and static structure factor are calculated with high accuracy over a range of conditions and compared w

  5. Simulating colloids with Baxter's adhesive hard sphere model

    NARCIS (Netherlands)

    Miller, M.A.; Frenkel, D.

    2004-01-01

    The structure of the Baxter adhesive hard sphere fluid is examined using computer simulation. The radial distribution function (which exhibits unusual discontinuities due to the particle adhesion) and static structure factor are calculated with high accuracy over a range of conditions and compared

  6. Monodisperse porous silicon spheres as anode materials for lithium ion batteries.

    Science.gov (United States)

    Wang, Wei; Favors, Zachary; Ionescu, Robert; Ye, Rachel; Bay, Hamed Hosseini; Ozkan, Mihrimah; Ozkan, Cengiz S

    2015-03-05

    Highly monodisperse porous silicon nanospheres (MPSSs) are synthesized via a simple and scalable hydrolysis process with subsequent surface-protected magnesiothermic reduction. The spherical nature of the MPSSs allows for a homogenous stress-strain distribution within the structure during lithiation and delithiation, which dramatically improves the electrochemical stability. To fully extract the real performance of the MPSSs, carbon nanotubes (CNTs) were added to enhance the electronic conductivity within the composite electrode structure, which has been verified to be an effective way to improve the rate and cycling performance of anodes based on nano-Si. The Li-ion battery (LIB) anodes based on MPSSs demonstrate a high reversible capacity of 3105 mAh g(-1). In particular, reversible Li storage capacities above 1500 mAh g(-1) were maintained after 500 cycles at a high rate of C/2. We believe this innovative approach for synthesizing porous Si-based LIB anode materials by using surface-protected magnesiothermic reduction can be readily applied to other types of SiOx nano/microstructures.

  7. Melting and freezing lines for a mixture of charged colloidal spheres with spindle-type phase diagram

    Science.gov (United States)

    Lorenz, Nina J.; Palberg, Thomas

    2010-09-01

    We have measured the phase behavior of a binary mixture of like-charged colloidal spheres with a size ratio of Γ =0.9 and a charge ratio of Λ =0.96 as a function of particle number density n and composition p. Under exhaustively deionized conditions, the aqueous suspension forms solid solutions of body centered cubic structure for all compositions. The freezing and melting lines as a function of composition show opposite behavior and open a wide, spindle shaped coexistence region. Lacking more sophisticated treatments, we model the interaction in our mixtures as an effective one-component pair energy accounting for number weighted effective charge and screening constant. Using this description, we find that within experimental error the location of the experimental melting points meets the range of melting points predicted for monodisperse, one-component Yukawa systems made in several theoretical approaches. We further discuss that a detailed understanding of the exact phase diagram shape including the composition dependent width of the coexistence region will need an extended theoretical treatment.

  8. Fabrication of Macro-porous β-zeolite by Using Colloidal Polystyrene Spheres as a Template

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A β-zeolite/polystyrene composite material was synthesized by co-deposition of mono-disperse polystyrene spheres and nano β-zeolite particles in aqueous suspension on a vertical substrate. Macro-porous β-zeolite was obtained after the polystyrene template was removed by calcination. The micro/macro-pore structure of the prepared β-zeolite was highly ordered. In comparison with other assembly methods, the co-deposition method could obtain a highly ordered macro-porous material with relatively large zeolite filling particles, and therefore the co-deposition of particles with different size is a promising method for the fabrication of macro-porous materials.

  9. Second virial coefficient at the critical point in a fluid of colloidal spheres plus depletants.

    Science.gov (United States)

    Tuinier, Remco; Feenstra, Maartje S

    2014-11-11

    Vliegenthart-Lekkerkerker (VL) criterion B2 = -6vc for second virial coefficient B2 at the critical (colloidal) gas-liquid point is considered for a mixture of spheres with volume vc plus depletants. For the onset of fluid-phase instability, the VL criterion holds for a wide range of shapes of direct attractive forces between hard-core spheres (Vliegenthart, G. A.; Lekkerkerker, H. N. W. J. Chem. Phys. 2000, 112, 5364). In the case of long-ranged attractions imposed indirectly via depletants, it is found that the VL relation fails. Instead, B2/vc at the critical point depends strongly on the sphere/depletant size ratio. By making the hard spheres sticky, we find that B2 moves gradually toward the VL criterion upon increasing the stickiness.

  10. Crystallization kinetics of polydisperse colloidal hard spheres. II. Binary mixtures.

    Science.gov (United States)

    Martin, S; Bryant, G; van Megen, W

    2005-02-01

    In this paper we present measurements of the crystallization kinetics of binary mixtures of two different sized hard sphere particles. The growth of the Bragg reflections over time were analyzed to yield the crystallite scattering vector, the total amount of crystal, and the average linear crystal size. It was observed that a particle size distribution skewed to higher sized particles has a less detrimental effect on the crystal structure than a skew to smaller sized particles. In the latter case we observe that initial crystallite growth occurs at only a small number of sites, with further crystallization sites developing at later times. Based on these measurements we elaborate further on the previously proposed growth mechanism whereby crystallization occurs in conjunction with a local fractionation process in the fluid, which significantly affects the kinetic growth of crystallites in polydisperse systems.

  11. 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.

  12. Efficient one-pot synthesis of monodisperse alkyl-terminated colloidal germanium nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Carolan, Darragh, E-mail: darragh.carolan@tyndall.ie; Doyle, Hugh, E-mail: hugh.doyle@tyndall.ie [University College Cork, Tyndall National Institute (Ireland)

    2014-12-15

    An efficient one-pot method for fabricating alkyl-capped germanium nanocrystals (Ge NCs) is reported. Ge NCs with a size of 3.9 ± 0.5 nm, are formed by co-reduction of germanium tetrachloride in the presence of n-butyltrichlorogermane, producing NCs with butyl-terminated surfaces. The advantage of this method is that it allows rapid synthesis and functionalisation of NCs with minimal post-synthetic purification requirements. TEM imaging showed that the Ge NCs are monodisperse and highly crystalline, while EDX and SAED confirmed the chemical identity and crystal phase of the NCs. FTIR and XPS confirmed that the Ge NCs were well passivated, with some oxidation of the nanocrystal surface. Optical spectroscopy of the NCs showed a strong absorbance in the UV region and an excitation wavelength dependent photoluminescence in the UV/violet. Time resolved photoluminescence measurements showed the presence of two nanosecond lifetime components, consistent with recombination of photogenerated excitons at low lying energy states present at the nanocrystal surface. Photoluminescence quantum yields were determined to be 37 %, one of the highest values reported for organically terminated Ge NCs.

  13. Simulating asymmetric colloidal mixture with adhesive hard sphere model.

    Science.gov (United States)

    Jamnik, A

    2008-06-21

    Monte Carlo simulation and Percus-Yevick (PY) theory are used to investigate the structural properties of a two-component system of the Baxter adhesive fluids with the size asymmetry of the particles of both components mimicking an asymmetric binary colloidal mixture. The radial distribution functions for all possible species pairs, g(11)(r), g(22)(r), and g(12)(r), exhibit discontinuities at the interparticle distances corresponding to certain combinations of n and m values (n and m being integers) in the sum nsigma(1)+msigma(2) (sigma(1) and sigma(2) being the hard-core diameters of individual components) as a consequence of the impulse character of 1-1, 2-2, and 1-2 attractive interactions. In contrast to the PY theory, which predicts the delta function peaks in the shape of g(ij)(r) only at the distances which are the multiple of the molecular sizes corresponding to different linear structures of successively connected particles, the simulation results reveal additional peaks at intermediate distances originating from the formation of rigid clusters of various geometries.

  14. Hard, soft, and sticky spheres for dynamical studies of disordered colloidal packings

    Science.gov (United States)

    Gratale, Matthew Daniel

    This thesis describes experiments which explore the role of interparticle interactions as a means to alter, and control, the properties of dense colloidal packings. The first set of experiments studied phonon modes in two-dimensional colloidal crystals composed of soft microgel particles with hard polystyrene particle dopants distributed randomly on the triangular lattice. By mixing hard and soft spheres we obtain close-packed lattices of spheres with random bond strength disorder, textit{i.e.,} the effective springs coupling nearest-neighbors are either very stiff, very soft, or of intermediate stiffness. Video microscopy, particle tracking, and covariance matrix techniques are employed to derive the phonon modes of the corresponding ``shadow'' crystals, thereby enabling us to study how bond strength disorder affects vibrational properties. Hard and soft particles participate equally in low frequency phonon modes, and the samples exhibit Debye-like density of states behavior characteristic of crystals at low frequency. For mid- and high-frequency phonons, the relative participation of hard versus soft particles in each mode is found to vary systematically with dopant concentration. The second set of experiments investigated depletion interaction potentials between micron-size colloidal particles induced by nanometer-scale micelles composed of the surfactant hexaethylene glycol monododecyl ether (C12E6). The strength and range of the depletion interaction is revealed to arise from variations in shape anisotropy of the rod-like surfactant micelles. This shape anisotropy increases with increasing sample temperature. By fitting the colloidal interaction potentials to theoretical models, we extract the rod-like micelle length and shape anisotropy as a function of temperature. This work introduces micelle shape anisotropy as a means to control interparticle interactions in colloidal suspensions, and shows how interparticle depletion potentials of micron-scale objects

  15. Phase diagram of mixtures of hard colloidal spheres and discs: A free-volume scaled-particle approach

    OpenAIRE

    Lekkerkerker, H. N. W.; Oversteegen, S.M.

    2004-01-01

    Phase diagrams of mixtures of colloidal hard spheres with hard discs are calculated by means of the free-volume theory. The free-volume fraction available to the discs is determined from scaled-particle theory. The calculations show that depletion induced phase separation should occur at low disc concentrations in systems now experimentally available. The gas–liquid equilibrium of the spheres becomes stable at comparable size ratios as with bimodal mixtures of spheres or mixtures of rods and ...

  16. Molecular dynamics of a dense fluid of polydisperse hard spheres

    OpenAIRE

    Sear, Richard P.

    2000-01-01

    Slow dynamics in a fluid are studied in one of the most basic systems possible: polydisperse hard spheres. Monodisperse hard spheres cannot be studied as the slow down in dynamics as the density is increased is preempted by crystallisation. As the dynamics slow they become more heterogeneous, the spread in the distances traveled by different particles in the same time increases. However, the dynamics appears to be less heterogeneous than in hard-sphere-like colloids at the same volume fractio...

  17. Measurement of the zero-field magnetic dipole moment of magnetizable colloidal silica spheres

    Energy Technology Data Exchange (ETDEWEB)

    Claesson, E M; Erne, B H; Bakelaar, I A; Kuipers, B W M; Philipse, A P [Van' t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht (Netherlands)

    2007-01-24

    The magnetic properties of dispersions of magnetic silica microspheres have been investigated by measuring the magnetization curves and the complex magnetic susceptibility as a function of frequency and field amplitude. The silica spheres appear to have a net permanent magnetic dipole moment, even in zero field, which is increased significantly after a temporary exposure of the silica colloids to a saturating magnetic field. The magnetic properties of the microparticles in zero field are discussed in terms of the number and the orientations of the embedded nanoparticle dipoles along an easy axis of magnetization in the absence of an external field.

  18. Testing the Derjaguin approximation for colloidal mixtures of spheres and disks.

    Science.gov (United States)

    Oversteegen, S M; Lekkerkerker, H N W

    2003-08-01

    The depletion potential between two large hard spheres due to the presence of hard disks has been derived up to first order in the number density of disks by Piech and Walz [J. Colloid Interface Sci. 232, 86 (2000)] using the Derjaguin approximation. Using the generalized Gibbs equation, we compare this depletion potential to the exact solution up to first order in density. The Derjaguin approximation turns out to be surprisingly accurate; for aspect ratios smaller than 0.25 the error is less than 1%.

  19. Phase diagram of mixtures of hard colloidal spheres and discs: a free-volume scaled-particle approach.

    Science.gov (United States)

    Oversteegen, S M; Lekkerkerker, H N W

    2004-02-01

    Phase diagrams of mixtures of colloidal hard spheres with hard discs are calculated by means of the free-volume theory. The free-volume fraction available to the discs is determined from scaled-particle theory. The calculations show that depletion induced phase separation should occur at low disc concentrations in systems now experimentally available. The gas-liquid equilibrium of the spheres becomes stable at comparable size ratios as with bimodal mixtures of spheres or mixtures of rods and spheres. Introducing finite thickness of the platelets gives rise to a significant lowering of the fluid branch of the binodal. Copyright 2004 American Institute of Physics

  20. Magnetohydrodynamic motion of a colloidal sphere with self-electrochemical surface reactions in a spherical cavity.

    Science.gov (United States)

    Hsieh, Tzu H; Keh, Huan J

    2013-02-21

    An analytical study is presented for the magnetic-field-induced motion of a colloidal sphere with spontaneous electrochemical reactions on its surface situated at the center of a spherical cavity filled with an electrolyte solution at the quasi-steady state. The zeta potential associated with the particle surface may have an arbitrary distribution, whereas the electric double layers adjoining the particle and cavity surfaces are taken to be thin relative to the particle size and the spacing between the solid surfaces. The electric current and magnetic flux density distributions are solved for the particle and fluid phases of arbitrary electric conductivities and magnetic permeabilities. Applying a generalized reciprocal theorem to the Stokes equations with a Lorentz force term resulting from these density distributions for the fluid motion, we obtain explicit formulas for the translational and angular velocities of the colloidal sphere valid for all values of the particle-to-cavity size ratio. The particle velocities decrease monotonically with an increase in this size ratio. For the limiting case of an infinitely large cavity, our result reduces to the relevant solution for an unconfined spherical particle. The boundary effect on the movement of the particle with interfacial self-electrochemical reactions induced by the magnetohydrodynamic force is equivalent to that in sedimentation and much stronger than that in general phoretic motions.

  1. Multicomponent adhesive hard sphere models and short-ranged attractive interactions in colloidal or micellar solutions.

    Science.gov (United States)

    Gazzillo, Domenico; Giacometti, Achille; Fantoni, Riccardo; Sollich, Peter

    2006-11-01

    We investigate the dependence of the stickiness parameters tij=1/(12tauij)--where the tauij are the conventional Baxter parameters--on the solute diameters sigmai and sigmaj in multicomponent sticky hard sphere (SHS) models for fluid mixtures of mesoscopic neutral particles. A variety of simple but realistic interaction potentials, utilized in the literature to model short-ranged attractions present in real solutions of colloids or reverse micelles, is reviewed. We consider: (i) van der Waals attractions, (ii) hard-sphere-depletion forces, (iii) polymer-coated colloids, and (iv) solvation effects (in particular hydrophobic bonding and attractions between reverse micelles of water-in-oil microemulsions). We map each of these potentials onto an equivalent SHS model by requiring the equality of the second virial coefficients. The main finding is that, for most of the potentials considered, the size-dependence of tij(T,sigmai,sigmaj) can be approximated by essentially the same expression, i.e., a simple polynomial in the variable sigmaisigmaj/sigmaij2, with coefficients depending on the temperature T, or--for depletion interactions--on the packing fraction eta0 of the depletant particles.

  2. Physics of Hard Sphere Experiment: Scattering, Rheology and Microscopy Study of Colloidal Particles

    Science.gov (United States)

    Cheng, Z.-D.; Zhu, J.; Phan, S.-E.; Russel, W. B.; Chaikin, P. M.; Meyer, W. V.

    2002-01-01

    The Physics of Hard Sphere Experiment has two incarnations: the first as a scattering and rheology experiment on STS-83 and STS-94 and the second as a microscopy experiment to be performed in the future on LMM on the space station. Here we describe some of the quantitative and qualitative results from previous flights on the dynamics of crystallization in microgravity and especially the observed interaction of growing crystallites in the coexistance regime. To clarify rheological measurements we also present ground based experiments on the low shear rate viscosity and diffusion coefficient of several hard sphere experiments at high volume fraction. We also show how these experiments will be performed with confocal microscopy and laser tweezers in our lab and as preparation for the phAse II experiments on LMM. One of the main aims of the microscopy study will be the control of colloidal samples using an array of applied fields with an eye toward colloidal architectures. Temperature gradients, electric field gradients, laser tweezers and a variety of switchable imposed surface patterns are used toward this control.

  3. Ultra-small-angle neutron scattering: a tool to study packing of relatively monodisperse polymer spheres and their binary mixtures.

    Science.gov (United States)

    Reynolds, Philip A; McGillivray, Duncan J; Jackson, Andrew J; White, John W

    2009-07-01

    We measured ultra-small-angle neutron scattering (USANS) from polymethylmethacrylate spheres tamped down in air. Two slightly polydisperse pure sphere sizes (1.5 and 7.5 microm diameters) and five mixtures of these were used. All were loose packed (packing fractions of 0.3-0.6) with nongravitational forces (e.g., friction) important, preventing close packing. The USANS data are rich in information on powder packing. A modified Percus-Yevick fluid model was used to parametrize the data-adequately but not well. The modifications required the introduction of small voids, less than the sphere size, and a parameter reflecting substantial deviation from the Percus-Yevick prediction of the sphere-sphere correlation function. The mixed samples fitted less well, and two further modifying factors were necessary. These were local inhomogeneities, where the concentration of same-size spheres, both large and small, deviated from the mean packing, and a factor accounting for the presence within these "clusters" of self-avoidance of the large spheres (that is, large spheres coated with more small spheres than Percus-Yevick would predict). The overall deviations from the hard-sphere Percus-Yevick model that we find here suggest that fluid models of loose packed powders are unlikely to be successful but lay the ground work for future theoretical and computational works.

  4. Observation of a shape-dependent density maximum in random prackigns and glasses of colloidal silica ellipsoids

    NARCIS (Netherlands)

    Sacanna, S.; Rossi, L.; Wouterse, A.; Philipse, A.P.

    2007-01-01

    We have measured the random packing density of monodisperse colloidal silica ellipsoids with a well-defined shape, gradually deviating from a sphere shape up to prolates with aspect ratios of about 5, to find for a colloidal system the first experimental observation for the density maximum (at an as

  5. Phase diagram of mixtures of hard colloidal spheres and discs: A free-volume scaled-particle approach

    NARCIS (Netherlands)

    Lekkerkerker, H.N.W.; Oversteegen, S.M.

    2004-01-01

    Phase diagrams of mixtures of colloidal hard spheres with hard discs are calculated by means of the free-volume theory. The free-volume fraction available to the discs is determined from scaled-particle theory. The calculations show that depletion induced phase separation should occur at low disc co

  6. Phase diagram of mixtures of hard colloidal spheres and discs: A free-volume scaled-particle approach

    NARCIS (Netherlands)

    Lekkerkerker, H.N.W.; Oversteegen, S.M.

    2004-01-01

    Phase diagrams of mixtures of colloidal hard spheres with hard discs are calculated by means of the free-volume theory. The free-volume fraction available to the discs is determined from scaled-particle theory. The calculations show that depletion induced phase separation should occur at low disc

  7. 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...

  8. Communication: radial distribution functions in a two-dimensional binary colloidal hard sphere system.

    Science.gov (United States)

    Thorneywork, Alice L; Roth, Roland; Aarts, Dirk G A L; Dullens, Roel P A

    2014-04-28

    Two-dimensional hard disks are a fundamentally important many-body model system in classical statistical mechanics. Despite their significance, a comprehensive experimental data set for two-dimensional single component and binary hard disks is lacking. Here, we present a direct comparison between the full set of radial distribution functions and the contact values of a two-dimensional binary colloidal hard sphere model system and those calculated using fundamental measure theory. We find excellent quantitative agreement between our experimental data and theoretical predictions for both single component and binary hard disk systems. Our results provide a unique and fully quantitative mapping between experiments and theory, which is crucial in establishing the fundamental link between structure and dynamics in simple liquids and glass forming systems.

  9. Correlation between dynamical and structural heterogeneities in colloidal hard-sphere suspensions

    Science.gov (United States)

    Golde, Sebastian; Palberg, Thomas; Schöpe, Hans Joachim

    2016-07-01

    Dynamical and structural heterogeneities have long been thought to play a key role in a unified picture of solidification in view of the two competitive processes of crystallization and vitrification. Here, we study these heterogeneities by means of a combination of dynamic and static light-scattering techniques applied to the simplest model system exhibiting crystallization and vitrification: the colloidal hard-sphere system. Our method enables us to quantify and correlate the temporal evolution of the amount of ordered clusters (precursors) and the amount of slow particles. Our analysis shows that their temporal evolutions are closely related and that there is an intimate link between structural and dynamic heterogeneities, crystal nucleation and the non-crystallization transition.

  10. Experimental observation of structural crossover in binary mixtures of colloidal hard spheres.

    Science.gov (United States)

    Baumgartl, Jörg; Dullens, Roel P A; Dijkstra, Marjolein; Roth, Roland; Bechinger, Clemens

    2007-05-11

    Using confocal microscopy, we investigate the structure of binary mixtures of colloidal hard spheres with size ratio q=0.61. As a function of the packing fraction of the two particle species, we observe a marked change of the dominant wavelength in the pair-correlation function. This behavior is in excellent agreement with a recently predicted structural crossover in such mixtures. In addition, the repercussions of structural crossover on the real-space structure of a binary fluid are analyzed. We suggest a relation between crossover and the lateral extension of networks containing only equally-sized particles that are connected by nearest-neighbor bonds. This is supported by Monte Carlo simulations which are performed at different packing fractions and size ratios.

  11. Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow

    KAUST Repository

    Cheng, X.

    2011-12-23

    Colloidal suspensions self-assemble into equilibrium structures ranging from face- and body-centered cubic crystals to binary ionic crystals, and even kagome lattices. When driven out of equilibrium by hydrodynamic interactions, even more diverse structures can be accessed. However, mechanisms underlying out-of-equilibrium assembly are much less understood, though such processes are clearly relevant in many natural and industrial systems. Even in the simple case of hard-sphere colloidal particles under shear, there are conflicting predictions about whether particles link up into string-like structures along the shear flow direction. Here, using confocal microscopy, we measure the shear-induced suspension structure. Surprisingly, rather than flow-aligned strings, we observe log-rolling strings of particles normal to the plane of shear. By employing Stokesian dynamics simulations, we address the mechanism leading to this out-of-equilibrium structure and show that it emerges from a delicate balance between hydrodynamic and interparticle interactions. These results demonstrate a method for assembling large-scale particle structures using shear flows.

  12. Motion of a colloidal sphere with interfacial self-electrochemical reactions induced by a magnetic field.

    Science.gov (United States)

    Hsieh, Tzu H; Keh, Huan J

    2012-05-07

    The motion of a spherical colloidal particle with spontaneous electrochemical reactions occurring on its surface in an ionic solution subjected to an applied magnetic field is analyzed for an arbitrary zeta potential distribution. The thickness of the electric double layer adjacent to the particle surface is assumed to be much less than the particle radius. The solutions of the Laplace equations governing the magnetic scalar potential and electric potential, respectively, lead to the magnetic flux and electric current density distributions in the particle and fluid phases of arbitrary magnetic permeabilities and electric conductivities. The Stokes equations modified with the Lorentz force contribution for the fluid motion are dealt by using a generalized reciprocal theorem, and closed-form formulas for the translational and angular velocities of the colloidal sphere induced by the magnetohydrodynamic effect are obtained. The dipole and quadrupole moments of the zeta potential distribution over the particle surface cause the particle translation and rotation, respectively. The induced velocities of the particle are unexpectedly significant, and their dependence on the characteristics of the particle-fluid system is physically different from that for electromagnetophoretic particles or phoretic swimmers.

  13. Communication: Dynamical density functional theory for dense suspensions of colloidal hard spheres.

    Science.gov (United States)

    Stopper, Daniel; Roth, Roland; Hansen-Goos, Hendrik

    2015-11-14

    We study structural relaxation of colloidal hard spheres undergoing Brownian motion using dynamical density functional theory. Contrary to the partial linearization route [D. Stopper et al., Phys. Rev. E 92, 022151 (2015)] which amounts to using different free energy functionals for the self and distinct part of the van Hove function G(r, t), we put forward a unified description employing a single functional for both components. To this end, interactions within the self part are removed via the zero-dimensional limit of the functional with a quenched self component. In addition, we make use of a theoretical result for the long-time mobility in hard-sphere suspensions, which we adapt to the inhomogeneous fluid. Our results for G(r, t) are in excellent agreement with numerical simulations even in the dense liquid phase. In particular, our theory accurately yields the crossover from free diffusion at short times to the slower long-time diffusion in a crowded environment.

  14. Motions in binary mixtures of hard colloidal spheres: melting of the glass.

    Science.gov (United States)

    Williams, S R; van Megen, W

    2001-10-01

    Dynamic light-scattering experiments are performed on binary mixtures of hard-sphere-like colloidal suspensions with a size ratio of 0.6. The optical properties of the particles are such that the relative contrast of the two species is very sensitive to temperature, a feature that is exploited to obtain the three partial coherent intermediate scattering functions. The glass transition is identified by the onset of structural arrest, or arrest of the alpha process, on the time scale of the experiment. This is observed in a one-component suspension at a packing fraction of 0.575. The intermediate scattering functions measured on the mixtures quantify how, on introduction of the smaller spheres, the alpha process is released, i.e., how the glass melts. Increasing the fraction of smaller particles causes the alpha process to speed up but, at a given wave vector, also incurs a change to its amplitude in proportion to the change in the (partial) structure factor.

  15. Modeling the Permittivity of Two-Phase Media Containing Monodisperse Spheres: Effects of Microstructure and Multiple Scattering

    OpenAIRE

    Doyle, Timothy E; Robinson, David A.; Scott B. Jones; Warnick, Keith H.; Carruth, Brent L.

    2007-01-01

    A numerical modeling approach was developed to predict the dielectric properties of heterogeneous particulate materials with arbitrary microstructures. To test the method, simulation and experimental data were acquired for the effective permittivities of various glass sphere suspensions. Both ordered lattices and random microstructures of up to 3600 spheres were modeled for volume fractions of 0.025–0.60. The electric fields in the suspensions were computed using an iterative multipole method...

  16. Monte Carlo simulations of the solid-liquid transition in hard spheres and colloid-polymer mixtures.

    Science.gov (United States)

    Zykova-Timan, T; Horbach, J; Binder, K

    2010-07-07

    Monte Carlo simulations at constant pressure are performed to study coexistence and interfacial properties of the liquid-solid transition in hard spheres and in colloid-polymer mixtures. The latter system is described as a one-component Asakura-Oosawa (AO) model where the polymer's degrees of freedom are incorporated via an attractive part in the effective potential for the colloid-colloid interactions. For the considered AO model, the polymer reservoir packing fraction is eta(p) (r)=0.1 and the colloid-polymer size ratio is q[triple bond]sigma(p)/sigma=0.15 (with sigma(p) and sigma as the diameter of polymers and colloids, respectively). Inhomogeneous solid-liquid systems are prepared by placing the solid fcc phase in the middle of a rectangular simulation box, creating two interfaces with the adjoined bulk liquid. By analyzing the growth of the crystalline region at various pressures and for different system sizes, the coexistence pressure p(co) is obtained, yielding p(co)=11.576 k(B)T/sigma(3) for the hard-sphere system and p(co)=8.00 k(B)T/sigma(3) for the AO model (with k(B) as the Boltzmann constant and T as the temperature). Several order parameters are introduced to distinguish between solid and liquid phases and to describe the interfacial properties. From the capillary-wave broadening of the solid-liquid interface, the interfacial stiffness is obtained for the (100) crystalline plane, giving the values gamma approximately 0.49 k(B)T/sigma(2) for the hard-sphere system and gamma approximately 0.95 k(B)T/sigma(2) for the AO model.

  17. Magnetohydrodynamic effects on a charged colloidal sphere with arbitrary double-layer thickness.

    Science.gov (United States)

    Hsieh, Tzu H; Keh, Huan J

    2010-10-01

    An analytical study is presented for the magnetohydrodynamic (MHD) effects on a translating and rotating colloidal sphere in an arbitrary electrolyte solution prescribed with a general flow field and a uniform magnetic field at a steady state. The electric double layer surrounding the charged particle may have an arbitrary thickness relative to the particle radius. Through the use of a simple perturbation method, the Stokes equations modified with an electric force term, including the Lorentz force contribution, are dealt by using a generalized reciprocal theorem. Using the equilibrium double-layer potential distribution from solving the linearized Poisson-Boltzmann equation, we obtain closed-form formulas for the translational and angular velocities of the spherical particle induced by the MHD effects to the leading order. It is found that the MHD effects on the particle movement associated with the translation and rotation of the particle and the ambient fluid are monotonically increasing functions of κa, where κ is the Debye screening parameter and a is the particle radius. Any pure rotational Stokes flow of the electrolyte solution in the presence of the magnetic field exerts no MHD effect on the particle directly in the case of a very thick double layer (κa→0). The MHD effect caused by the pure straining flow of the electrolyte solution can drive the particle to rotate, but it makes no contribution to the translation of the particle.

  18. Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Force, torque, translation, and rotation

    Energy Technology Data Exchange (ETDEWEB)

    Zia, Roseanna N., E-mail: zia@cbe.cornell.edu; Su, Yu [Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853 (United States); Swan, James W. [Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2015-12-14

    The formulation of detailed models for the dynamics of condensed soft matter including colloidal suspensions and other complex fluids requires accurate description of the physical forces between microstructural constituents. In dilute suspensions, pair-level interactions are sufficient to capture hydrodynamic, interparticle, and thermodynamic forces. In dense suspensions, many-body interactions must be considered. Prior analytical approaches to capturing such interactions such as mean-field approaches replace detailed interactions with averaged approximations. However, long-range coupling and effects of concentration on local structure, which may play an important role in, e.g., phase transitions, are smeared out in such approaches. An alternative to such approximations is the detailed modeling of hydrodynamic interactions utilizing precise couplings between moments of the hydrodynamic traction on a suspended particle and the motion of that or other suspended particles. For two isolated spheres, a set of these functions was calculated by Jeffrey and Onishi [J. Fluid Mech. 139, 261–290 (1984)] and Jeffrey [J. Phys. Fluids 4, 16–29 (1992)]. Along with pioneering work by Batchelor, these are the touchstone for low-Reynolds-number hydrodynamic interactions and have been applied directly in the solution of many important problems related to the dynamics of dilute colloidal dispersions [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375–400 (1972) and G. K. Batchelor, J. Fluid Mech. 74, 1–29 (1976)]. Toward extension of these functions to concentrated systems, here we present a new stochastic sampling technique to rapidly calculate an analogous set of mobility functions describing the hydrodynamic interactions between two hard spheres immersed in a suspension of arbitrary concentration, utilizing accelerated Stokesian dynamics simulations. These mobility functions provide precise, radially dependent couplings of hydrodynamic force and torque to particle

  19. Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Force, torque, translation, and rotation

    Science.gov (United States)

    Zia, Roseanna N.; Swan, James W.; Su, Yu

    2015-12-01

    The formulation of detailed models for the dynamics of condensed soft matter including colloidal suspensions and other complex fluids requires accurate description of the physical forces between microstructural constituents. In dilute suspensions, pair-level interactions are sufficient to capture hydrodynamic, interparticle, and thermodynamic forces. In dense suspensions, many-body interactions must be considered. Prior analytical approaches to capturing such interactions such as mean-field approaches replace detailed interactions with averaged approximations. However, long-range coupling and effects of concentration on local structure, which may play an important role in, e.g., phase transitions, are smeared out in such approaches. An alternative to such approximations is the detailed modeling of hydrodynamic interactions utilizing precise couplings between moments of the hydrodynamic traction on a suspended particle and the motion of that or other suspended particles. For two isolated spheres, a set of these functions was calculated by Jeffrey and Onishi [J. Fluid Mech. 139, 261-290 (1984)] and Jeffrey [J. Phys. Fluids 4, 16-29 (1992)]. Along with pioneering work by Batchelor, these are the touchstone for low-Reynolds-number hydrodynamic interactions and have been applied directly in the solution of many important problems related to the dynamics of dilute colloidal dispersions [G. K. Batchelor and J. T. Green, J. Fluid Mech. 56, 375-400 (1972) and G. K. Batchelor, J. Fluid Mech. 74, 1-29 (1976)]. Toward extension of these functions to concentrated systems, here we present a new stochastic sampling technique to rapidly calculate an analogous set of mobility functions describing the hydrodynamic interactions between two hard spheres immersed in a suspension of arbitrary concentration, utilizing accelerated Stokesian dynamics simulations. These mobility functions provide precise, radially dependent couplings of hydrodynamic force and torque to particle translation

  20. Tailored synthesis of monodispersed nano/submicron porous silicon oxycarbide (SiOC) spheres with improved Li-storage performance as an anode material for Li-ion batteries

    Science.gov (United States)

    Shi, Huimin; Yuan, Anbao; Xu, Jiaqiang

    2017-10-01

    A spherical silicon oxycarbide (SiOC) material (monodispersed nano/submicron porous SiOC spheres) is successfully synthesized via a specially designed synthetic strategy involving pyrolysis of phenyltriethoxysilane derived pre-ceramic polymer spheres at 900 °C. In order to prevent sintering of the pre-ceramic polymer spheres upon heating, a given amount of hollow porous SiO2 nanobelts which are separately prepared from tetraethyl orthosilicate with CuO nanobelts as templates are introduced into the pre-ceramic polymer spheres before pyrolysis. This material is investigated as an anode for lithium-ion batteries in comparison with the large-size bulk SiOC material synthesized under the similar conditions but without hollow SiO2 nanobelts. The maximum reversible specific capacity of ca. 900 mAh g-1 is delivered at the current density of 100 mA g-1 and ca. 98% of the initial capacity is remained after 100 cycles at 100 mA g-1 for the SiOC spheres material, which are much superior to the bulk SiOC material. The improved lithium storage performance in terms of specific capacity and cyclability is attributed to its particular morphology of monodisperse nano/submicron porous spheres as well as its modified composition and microstructure. This SiOC material has higher Li-storage activity and better stability against volume expansion during repeated lithiation and delithiation cycling.

  1. Large difference in the elastic properties of fcc and hcp hard-sphere crystals

    NARCIS (Netherlands)

    Pronk, S.; Frenkel, D.

    2003-01-01

    We report a numerical calculation of the elastic constants of the fcc and hcp crystal phases of monodisperse hard-sphere colloids. Surprisingly, some of these elastic constants are very different (up to 20%), even though the free-energy, pressure, and bulk compressibility of the two crystal structur

  2. 胶质碳球为模板制备NiO空心球%Synthesis of NiO Hollow Spheres Using Colloidal Carbon Spheres as Template

    Institute of Scientific and Technical Information of China (English)

    武拥建; 郑明涛; 谢春林; 靳权; 易观贵; 刘应亮

    2011-01-01

    以胶质碳球为模板、六亚甲基四胺为沉淀剂,在乙醇中溶剂热反应,再经500℃煅烧6h制备了NiO空心球.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)和低温氮吸附-脱附,对NiO的结构和形貌进行了表征.结果表明溶剂热反应时间是制备完整NiO空心球的关键因素,溶剂热反应12h,再经空气中煅烧,可制得形貌均一的NiO空心球.所得产物是由NiO纳米粒子组装而成的具有多孔结构的空心球.同时,本文对NiO空心球结构的形成过程和可能机理进行了分析和讨论.%NiO hollow spheres were synthesized by a solvothermal reaction using colloidal carbon spheres (CCS) as sacricial template and hexamethylenetetramine (HMT) as precipitating agent in ethanol,and then calcined at 500 ℃ for 6 h.The characteristics of these NiO hollow spheres samples were characterized by XRD,SEM,TEM,FTIR and low temperature nitrogen adsorption-desorption isotherms.The results show that solvothermal reaction time is crucial to the integrity of the hollow spheres.The well defined NiO hollow spheres can be synthesized through 12 h solvothermal treatment and then calcination in air.The as-synthesized NiO hollow spheres have the porous wall consisted of nanosized particles.Moreover,the formation mechanism of NiO hollow spheres is also discussed.

  3. Influence of α-amylase template concentration on systematic entrapment of highly stable and monodispersed colloidal gold nanoparticles

    Science.gov (United States)

    Ananth, A. Nitthin; Ananth, A. Nimrodh; Jose, Sujin P.; Umapathy, S.; Mathavan, T.

    2016-01-01

    Nano gold / α-amylase colloidal dispersions of profound stability were made using simple procedure with a conventional reducing agent. The surface plasmon resonance of the gold nanocrystals was used to quantify the extent of the dispersion stability and functionalization. It is found that the reduced gold nanoparticles were trapped into the protein network without denaturation the structure of α-amylase protein. This kind of entrapment of particles into the protein network prevents clustering of individual gold nanoparticles (6.42 nm ± 0.92 nm) by acting as a natural spacer. Systematic entrapment was facilitated by the affinity of gold to the sulfur moieties (Au-S) in the protein structure.

  4. A Monte Carlo Study of Influences on Depletion Force from Another Large Sphere in Colloidal Suspensions

    Institute of Scientific and Technical Information of China (English)

    XIAO Chang-Ming; GUO Ji-Yuan; HU Ping

    2006-01-01

    @@ According to the acceptance ratio method, the influences on the depletion interactions between a large sphere and a plate from another closely placed large sphere are studied by Monte Carlo simulation. The numerical results show that both the depletion potential and depletion force are affected by the presence of the closely placed large sphere; the closer the large sphere are placed to them, the larger the influence will be. Furthermore, the influences on the depletion interactions from another large sphere are more sensitive to the angle than to the distance.

  5. When shape is enough: from colloidal spheres to twisted polyhedra, from icosahedral to chiral order

    NARCIS (Netherlands)

    Dussi, S.|info:eu-repo/dai/nl/372628885

    2016-01-01

    In this thesis, we study entropy-driven phase transitions in suspensions of colloidal particles. Colloids are small particles, with typical sizes ranging from the nanometer to the micron, dispersed in a medium that is composed of much smaller particles (atoms or molecules). Because of this size diff

  6. Rapid Preparation of Monodisperse Nano-Silver Colloids Using Microwave Irradiation%微波法快速制备单分散纳米银溶胶

    Institute of Scientific and Technical Information of China (English)

    徐光年; 乔学亮; 邱小林; 陈建国

    2012-01-01

    不添加任何还原剂,在PVP保护下通过微波辐射[Ag(NH3)2]OH络合物水溶液激发自由电子还原Ag+形成纳米银溶胶.UV-Vis吸收光谱测试表明,胶态纳米银粒子的吸光度随微波辐射时间的延长而增加,但最大吸收波长基本不变.当Ag+/PVP质量比为1:8,微波辐射时间为5 min时,吸光度趋于稳定.TEM观测和图像分析结果表明,纳米银粒子的形貌为球形、单分散、平均粒径1.36 nm、标准偏差0.54 nm.%The Ag+ were reduced to elemental silver by free-electron from microwave radiation [Ag(NH3)2]OH complex aqueous solution without any reducing agent, and the nano-silver sol was formed under the protection of PVP. UV-Vis absorption spectra show that the absorbance of the colloidal silver nanoparticles increases with the radiation time, but the maximal absorption wavelength does not change. The absorbance keeps stable when the microwave radiation time is up to 5 min at the mass ratio of Ag7PVP=l:8. TEM observation and image analysis results show that the morphology of nano-silver particles are spherical and monodisperse, with an average diameter of 1.36 nm and the standard deviation of 0.54 nm.

  7. Fabrication of Colloidal Laves Phases via Hard Tetramers and Hard Spheres: Bulk Phase Diagram and Sedimentation Behavior.

    Science.gov (United States)

    Avvisati, Guido; Dasgupta, Tonnishtha; Dijkstra, Marjolein

    2017-08-22

    Colloidal photonic crystals display peculiar optical properties that make them particularly suitable for application in different fields. However, the low packing fraction of the targeted structures usually poses a real challenge in the fabrication stage. Here, we propose a route to colloidal photonic crystals via a binary mixture of hard tetramers and hard spheres. By combining theory and computer simulations, we calculate the phase diagram as well as the stacking diagram of the mixture and show that a colloidal analogue of the MgCu2 Laves phase-which can serve as a precursor of a photonic band-gap structure-is a thermodynamically stable phase in a large region of the phase diagram. Our findings show a relatively large coexistence region between the fluid and the Laves phase, which is potentially accessible by experiments. Furthermore, we determine the sedimentation behavior of the suggested mixture, by identifying several stacking sequences in the sediment. Our work uncovers a self-assembly path toward a photonic structure with a band gap in the visible region.

  8. Fabrication of Colloidal Laves Phases via Hard Tetramers and Hard Spheres: Bulk Phase Diagram and Sedimentation Behavior

    Science.gov (United States)

    2017-01-01

    Colloidal photonic crystals display peculiar optical properties that make them particularly suitable for application in different fields. However, the low packing fraction of the targeted structures usually poses a real challenge in the fabrication stage. Here, we propose a route to colloidal photonic crystals via a binary mixture of hard tetramers and hard spheres. By combining theory and computer simulations, we calculate the phase diagram as well as the stacking diagram of the mixture and show that a colloidal analogue of the MgCu2 Laves phase—which can serve as a precursor of a photonic band-gap structure—is a thermodynamically stable phase in a large region of the phase diagram. Our findings show a relatively large coexistence region between the fluid and the Laves phase, which is potentially accessible by experiments. Furthermore, we determine the sedimentation behavior of the suggested mixture, by identifying several stacking sequences in the sediment. Our work uncovers a self-assembly path toward a photonic structure with a band gap in the visible region. PMID:28787126

  9. Electric-Field-Induced Lock-and-Key Interactions between Colloidal Spheres and Bowls

    NARCIS (Netherlands)

    Kamp, Marlous; Elbers, Nina A.; Troppenz, Thomas; Imhof, Arnout; Dijkstra, Marjolein; Van Roij, René; Van Blaaderen, Alfons

    2016-01-01

    To realize new and directed self-assembly (SA) pathways, the focus in colloid science and nanoscience has shifted from spherical particles and interactions to increasingly more complex shapes and interparticle potentials. This field is fueled by recent breakthroughs in particle synthesis, such as

  10. Measurement of the zero-field magnetic dipole moment of magnetizable colloidal silica spheres

    NARCIS (Netherlands)

    Claesson, E.M.; Erne, B.H.; Bakelaar, I.A.; Kuipers, B.W.M.; Philipse, A.P.

    2007-01-01

    The magnetic properties of dispersions of magnetic silica microspheres have been investigated by measuring the magnetization curves and the complex magnetic susceptibility as a function of frequency and field amplitude. The silica spheres appear to have a net permanent magnetic dipole moment, even i

  11. Slanted stacking faults and persistent face centered cubic crystal growth in sedimentary colloidal hard sphere crystals

    NARCIS (Netherlands)

    Hilhorst, J.; Wolters, J. R.; Petukhov, A.V.

    2010-01-01

    Hard sphere crystal growth is a delicate interplay between kinetics and thermodynamics, where the former is commonly thought to favour a random hexagonal close packed structure and the latter leads to a face centered cubic crystal. In this article, we discuss the influence of slanted stacking faults

  12. Density functional theory for colloidal mixtures of hard platelets, rods, and spheres.

    Science.gov (United States)

    Esztermann, Ansgar; Reich, Hendrik; Schmidt, Matthias

    2006-01-01

    A geometry-based density-functional theory is presented for mixtures of hard spheres, hard needles, and hard platelets; both the needles and platelets are taken to be of vanishing thickness. Geometrical weight functions that are characteristic for each species are given, and it is shown how convolutions of pairs of weight functions recover each Mayer bond of the ternary mixture and hence ensure the correct second virial expansion of the excess free-energy functional. The case of sphere-platelet overlap relies on the same approximation as does Rosenfeld's functional for strictly two-dimensional hard disks. We explicitly control contributions to the excess free energy that are of third order in density. Analytic expressions relevant for the application of the theory to states with planar translational and cylindrical rotational symmetry--e.g., to describe behavior at planar smooth walls--are given. For binary sphere-platelet mixtures, in the appropriate limit of small platelet densities, the theory differs from that used in a recent treatment [L. Harnau and S. Dietrich, Phys. Rev. E 71, 011504 (2004)]. As a test case of our approach we consider the isotropic-nematic bulk transition of pure hard platelets, which we find to be weakly first order, with values for the coexistence densities and the nematic order parameter that compare well with simulation results.

  13. Colloidal and micro-carbon spheres derived from low-temperature polymerization reactions.

    Science.gov (United States)

    Moreno-Castilla, Carlos

    2016-10-01

    Carbon spheres (CSs) have recently attracted major interest due to their new applications, mainly in energy storage and conversion but also in hard-templating, sorption/catalysis processes, and drug delivery systems. This is attributable to their physico-chemical properties, including their tunable morphology (solid, hollow and core-shell), size, surface area/porosity, good electrical conductivity, low external surface-to-volume ratio, high packing density, enhanced mass transport, robust mechanical stability, low cytotoxicity, and excellent biocompatibility. They can be obtained from a wide variety of carbon precursors and methods. This review covers their production by carbonization of polymer spheres from low-temperature polymerization reactions, considered here as below 250°C. This is a very important method because it allows the synthesis of CSs with different morphologies and doped with other elements or chemical compounds. The preparation of polymer spheres by this technique is well documented in the literature, and the objective of this review is to summarize and give an overview of the most significant publications, proposing a novel classification based on the formation mechanism of the polymer spheres. This classification includes the following polymerization processes: emulsion polymerization and its derivatives, seeded emulsion and inverse emulsion polymerization; precipitation polymerization and its derivative, dispersion polymerization; hard-templating; spray-drying; and hydrothermal or solvothermal treatment of carbohydrates and biomass in general. This review also reports on the morphology and surface characteristics of the CSs obtained by different synthetic approaches. The final section of the review describes the current applications of these CSs, notably in energy storage (supercapacitors and rechargeable batteries) and energy conversion (fuel cells and dye-sensitized solar cells). Besides the numerous applications listed above, they are

  14. Equivalence of glass transition and colloidal glass transition in the hard-sphere limit.

    Science.gov (United States)

    Xu, Ning; Haxton, Thomas K; Liu, Andrea J; Nagel, Sidney R

    2009-12-11

    We show that the slowing of the dynamics in simulations of several model glass-forming liquids is equivalent to the hard-sphere glass transition in the low-pressure limit. In this limit, we find universal behavior of the relaxation time by collapsing molecular-dynamics data for all systems studied onto a single curve as a function of T/p, the ratio of the temperature to the pressure. At higher pressures, there are deviations from this universal behavior that depend on the interparticle potential, implying that additional physical processes must enter into the dynamics of glass formation.

  15. Principal component analysis of persistent homology rank functions with case studies of spatial point patterns, sphere packing and colloids

    Science.gov (United States)

    Robins, Vanessa; Turner, Katharine

    2016-11-01

    Persistent homology, while ostensibly measuring changes in topology, captures multiscale geometrical information. It is a natural tool for the analysis of point patterns. In this paper we explore the statistical power of the persistent homology rank functions. For a point pattern X we construct a filtration of spaces by taking the union of balls of radius a centred on points in X, Xa =∪x∈X B(x , a) . The rank function βk(X) : {(a , b) ∈R2 : a ≤ b } → R is then defined by βk(X) (a , b) = rank(ι∗ :Hk(Xa) →Hk(Xb)) where ι∗ is the induced map on homology from the inclusion map on spaces. We consider the rank functions as lying in a Hilbert space and show that under reasonable conditions the rank functions from multiple simulations or experiments will lie in an affine subspace. This enables us to perform functional principal component analysis which we apply to experimental data from colloids at different effective temperatures and to sphere packings with different volume fractions. We also investigate the potential of rank functions in providing a test of complete spatial randomness of 2D point patterns using the distances to an empirically computed mean rank function of binomial point patterns in the unit square.

  16. Design of fibers spun from carbon nanotube-sphere binary colloidal systems as substrates for cell behaviour control

    Science.gov (United States)

    Polizu, Stefania

    The aim of this work is to design new carbon nanotube neural biomaterials shaped as fibers, where the biodegradability and biocompatibility are achieved. Capitalizing on wet spinning process, we propose a hybrid approach allowing the integration of carbon nanotubes (CNTs) in macroscopic fibers with biodegradable and biocompatible responses. This new fabrication method use the wet spinning process which eludes the CNT's covalent chemistry, thus preserving the intrinsic characteristics of nanotubes. Our concept is based on the development of a spinnable Nanotube-Sphere Binary Colloidal System (NSBCS) for a wet spinning process. It contains CNTs dispersed with sodium dodecyl sulphate (SDS) and an aqueous suspension of polylactic-co-glycolic acid (PLGA) nanoparticles combined in a variety of ratios. The efficiency of this method resides in the synergistic effect of spherical nanoparticles and rod-like particles assembled in a binary colloid system which plays a main role in the spinning process. The configuration of mixture dispersions at sub-microscopic and microscopic level is related to the spatial confinement created by the gaps between spherical particles. They ensure the insertion of nanotubes in the PLGA lattice and assist the formation of the fiber during the spinning process. A spatial confinement is induced through the insertion of nanotubes between the nanoparticles. It is further increased by the passage of the mixture from cylindrical syringe's needle to conical nozzle, during the injection of the mixture into the coagulation bath. At this stage of the process, the combination of the confinement effect with the shear flow action is advantageous. The method we propose promotes the spinning of CNT macroscopic fibers from a binary colloidal mixture containing CNTs combined with PLGA nanoparticles in a variety of ratios, thus resulting in fibers with various CNT content. PLGA spherical nanoparticles root the structuring of fibers, thus improving the

  17. Self-Assembly Kinetics of Colloidal Particles inside Monodispersed Micro-Droplet and Fabrication of Anisotropic Photonic Crystal Micro-Particles

    Directory of Open Access Journals (Sweden)

    Ming-Yu Zhang

    2016-09-01

    Full Text Available A new microfluidic approach to preparing anisotropic colloidal photonic crystal microparticles is developed and the self-assembly kinetics of colloidal nanoparticles is discussed. Based on the “coffee ring” effect in the self-assembly process of colloidal silica particle in strong solvent extraction environment, we successfully prepared anisotropic photonic crystal microparticles with different shapes and improved optical properties. The shapes and optical properties of photonic crystal microparticles can be controlled by adjusting the droplet size and extraction rate. We studied the self-assembly mechanism of colloidal silica particles in strong solvent extraction environment, which has potential applications in a variety of fields including optical communication technology, environmental response, photo-catalysis and chromic material.

  18. Generation of colloidal granules and capsules from double emulsion drops

    Science.gov (United States)

    Hess, Kathryn S.

    Assemblies of colloidal particles are extensively used in ceramic processing, pharmaceuticals, inks and coatings. In this project, the aim was to develop a new technique to fabricate monodispersed colloidal assemblies. The use of microfluidic devices and emulsion processing allows for the fabrication of complex materials that can be used in a variety of applications. A microfluidic device is used to create monodispersed water/oil/water (w/o/w) double emulsions with interior droplets of colloidal silica suspension ranging in size from tens to hundreds of microns. By tailoring the osmotic pressure using glycerol as a solute in the continuous and inner phases of the emulsion, we can control the final volume size of the monodispersed silica colloidal crystals that form in the inner droplets of the double emulsion. Modifying the ionic strength in the colloidal dispersion can be used to affect the particle-particle interactions and crystal formation of the final colloidal particle. This w/o/w technique has been used with other systems of metal oxide colloids and cellulose nanocrystals. Encapsulation of the colloidal suspension in a polymer shell for the generation of ceramic-polymer core-shell particles has also been developed. These core-shell particles have spawned new research in the field of locally resonant acoustic metamaterials. Systems and chemistries for creating cellulose hydrogels within the double emulsions have also been researched. Water in oil single emulsions and double emulsions have been used to create cellulose hydrogel spheres in the sub-100 micron diameter range. Oil/water/oil double emulsions allow us to create stable cellulose capsules. The addition of a second hydrogel polymer, such as acrylate or alginate, further strengthens the cellulose gel network and can also be processed into capsules and particles using the microfluidic device. This work could have promising applications in acoustic metamaterials, personal care products, pharmaceuticals

  19. Phase equilibria in polydisperse nonadditive hard-sphere systems.

    Science.gov (United States)

    Paricaud, Patrice

    2008-08-01

    Colloidal particles naturally exhibit a size polydispersity that can greatly influence their phase behavior in solution. Nonadditive hard-sphere (NAHS) mixtures are simple and well-suited model systems to represent phase transitions in colloid systems. Here, we propose an analytical equation of state (EOS) for NAHS fluid mixtures, which can be straightforwardly applied to polydisperse systems. For positive values of the nonadditivity parameter Delta the model gives accurate predictions of the simulated fluid-fluid coexistence curves and compressibility factors. NPT Monte Carlo simulations of the mixing properties of the NAHS symmetric binary mixture with Delta>0 are reported. It is shown that the enthalpy of mixing is largely positive and overcomes the positive entropy of mixing when the pressure is increased, leading to a fluid-fluid phase transition with a lower critical solution pressure. Phase equilibria in polydisperse systems are predicted with the model by using the density moment formalism [P. Sollich, Adv. Chem. Phys. 116, 265 (2001)]. We present predictions of the cloud and shadow curves for polydisperse NAHS systems composed of monodisperse spheres and polydisperse colloid particles. A fixed nonadditivity parameter Delta > 0 is assumed between the monodisperse and polydisperse spheres, and a Schulz distribution is used to represent the size polydispersity. Polydispersity is found to increase the extent of the immiscibility region. The predicted cloud and shadow curves depend dramatically on the upper cutoff diameter sigmac of the Schulz distribution, and three-phase equilibria can occur for large values of sigmac.

  20. A General Synthesis Strategy for Hierarchical Porous Metal Oxide Hollow Spheres

    Directory of Open Access Journals (Sweden)

    Huadong Fu

    2015-01-01

    Full Text Available The hierarchical porous TiO2 hollow spheres were successfully prepared by using the hydrothermally synthesized colloidal carbon spheres as templates and tetrabutyl titanate as inorganic precursors. The diameter and wall thickness of hollow TiO2 spheres were determined by the hard templates and concentration of tetrabutyl titanate. The particle size, dispersity, homogeneity, and surface state of the carbon spheres can be easily controlled by adjusting the hydrothermal conditions and adding certain amount of the surfactants. The prepared hollow spheres possessed the perfect spherical shape, monodispersity, and hierarchically pore structures, and the further experiment verified that the present approach can be used to prepare other metal oxide hollow spheres, which could be used as catalysis, fuel cells, lithium-air battery, gas sensor, and so on.

  1. From 2D to 3D: Critical Casimir interactions and phase behavior of colloidal hard spheres in a near-critical solvent

    Science.gov (United States)

    Tasios, Nikos; Dijkstra, Marjolein

    2017-04-01

    Colloids dispersed in a binary solvent mixture experience long-ranged solvent-mediated interactions (critical Casimir forces) upon approaching the critical demixing point of the solvent mixture. The range of the interaction is set by the bulk correlation length of the solvent mixture, which diverges upon approaching the critical point. This presents a great opportunity to realize the reversible self-assembly of colloids by tuning the proximity to the critical point of the solvent. Here, we develop a rejection-free geometric cluster algorithm to study the full ternary mixture of colloidal hard spheres suspended in an explicit three-dimensional lattice model for the solvent mixture using extensive Monte Carlo simulations. The phase diagram displays stable colloidal gas, liquid, and crystal phases, as well as broad gas-liquid and gas-crystal phase coexistence, and pronounced fractionation of the solvent in the coexisting colloid phases. The topology of the phase diagram in our three-dimensional study shows striking resemblance to that of our previous studies carried out in two dimensions.

  2. Synthesis of highly uniform Cu2O spheres by a two-step approach and their assembly to form photonic crystals with a brilliant color

    Science.gov (United States)

    Su, Xin; Chang, Jie; Wu, Suli; Tang, Bingtao; Zhang, Shufen

    2016-03-01

    Monodisperse semiconductor colloidal spheres with a high refractive index hold great potential for building photonic crystals with a strong band gap, but the difficulty in separating the nucleation and growth processes makes it challenging to prepare highly uniform semiconductor colloidal spheres. Herein, real monodisperse Cu2O spheres were prepared via a hot-injection & heating-up two-step method using diethylene glycol as a milder reducing agent. The diameter of the as prepared Cu2O spheres can be tuned from 90 nm to 190 nm precisely. The SEM images reveal that the obtained Cu2O spheres have a narrow size distribution, which permits their self-assembly to form photonic crystals. The effects of precursor concentration and heating rates on the size and morphology of the Cu2O spheres were investigated in detail. The results indicate that the key points of the method include the burst nucleation to form seeds at a high temperature followed by rapid cooling to prevent agglomeration, and appropriate precursor concentration as well as a moderate growth rate during the further growth process. Importantly, photonic crystal films exhibiting a brilliant structural color were fabricated with the obtained monodisperse Cu2O spheres as building blocks, proving the possibility of making photonic crystals with a strong band gap. The developed method was also successfully applied to prepare monodisperse CdS spheres with diameters in the range from 110 nm to 210 nm.Monodisperse semiconductor colloidal spheres with a high refractive index hold great potential for building photonic crystals with a strong band gap, but the difficulty in separating the nucleation and growth processes makes it challenging to prepare highly uniform semiconductor colloidal spheres. Herein, real monodisperse Cu2O spheres were prepared via a hot-injection & heating-up two-step method using diethylene glycol as a milder reducing agent. The diameter of the as prepared Cu2O spheres can be tuned from 90 nm to

  3. Diffusing wave spectroscopy study of the colloidal interactions occurring between casein micelles and emulsion droplets: comparison to hard-sphere behavior.

    Science.gov (United States)

    Gaygadzhiev, Zafir; Corredig, Milena; Alexander, Marcela

    2008-04-15

    Understanding the underlying processes that govern interparticle interactions in colloidal systems is fundamental to predicting changes in their bulk properties. In this paper we discuss the colloidal behavior of casein micelles and protein-stabilized fat globules individually and in a mixture. The colloidal interactions were observed by transmission diffusing wave spectroscopy. The turbidity parameter, l*, and the diffusion coefficients of the samples studied were measured experimentally and compared to the theoretically calculated parameters for a hard-sphere system. The light scattering properties of casein micelles (volume fraction phi = 0.1-0.2) dispersed in milk permeate showed no deviation from the theoretically predicted model. Whey protein isolate (WPI)-stabilized emulsions (phi = 0.025-0.1) prepared either in milk permeate or in 5 mM imidazole buffer at pH 6.8 showed a behavior identical to that of the hard-sphere model. Similarly to the WPI-stabilized fat globules, the sodium caseinate (NaCas)-stabilized emulsions (phi = 0.025-0.1) prepared in milk permeate also showed resemblance to the theory. In contrast, NaCas-stabilized emulsions prepared in 5 mM imidazole buffer exhibited some discrepancy from the theoretically calculated parameters. The deviation from theory is attributed to the enhanced steric stabilization properties of these droplets in a low ionic strength environment. When recombined milks made from concentrated milk and WPI- and NaCas-stabilized droplets prepared in permeate (phi = 0.125-0.2) were studied, the experimental data showed a significant deviation from the theoretical behavior of a hard-sphere model due to mixing of two different species.

  4. Detecting Phase Boundaries in Hard-Sphere Suspensions

    Science.gov (United States)

    McDowell, Mark; Rogers, Richard B.; Gray, Elizabeth

    2009-01-01

    A special image-data-processing technique has been developed for use in experiments that involve observation, via optical microscopes equipped with electronic cameras, of moving boundaries between the colloidal-solid and colloidal-liquid phases of colloidal suspensions of monodisperse hard spheres. During an experiment, it is necessary to adjust the position of a microscope to keep the phase boundary within view. A boundary typically moves at a speed of the order of microns per hour. Because an experiment can last days or even weeks, it is impractical to require human intervention to keep the phase boundary in view. The present image-data-processing technique yields results within a computation time short enough to enable generation of automated-microscope-positioning commands to track the moving phase boundary

  5. Solvothermal synthesis of monodisperse LiFePO4 micro hollow spheres as high performance cathode material for lithium ion batteries.

    Science.gov (United States)

    Yang, Shiliu; Hu, Mingjun; Xi, Liujiang; Ma, Ruguang; Dong, Yucheng; Chung, C Y

    2013-09-25

    A microspherical, hollow LiFePO4 (LFP) cathode material with polycrystal structure was simply synthesized by a solvothermal method using spherical Li3PO4 as the self-sacrificed template and FeCl2·4H2O as the Fe(2+) source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the LFP micro hollow spheres have a quite uniform size of ~1 μm consisting of aggregated nanoparticles. The influences of solvent and Fe(2+) source on the phase and morphology of the final product were chiefly investigated, and a direct ion exchange reaction between spherical Li3PO4 templates and Fe(2+) ions was firstly proposed on the basis of the X-ray powder diffraction (XRD) transformation of the products. The LFP nanoparticles in the micro hollow spheres could finely coat a uniform carbon layer ~3.5 nm by a glucose solution impregnating-drying-sintering process. The electrochemical measurements show that the carbon coated LFP materials could exhibit high charge-discharge capacities of 158, 144, 125, 101, and even 72 mAh g(-1) at 0.1, 1, 5, 20, and 50 C, respectively. It could also maintain 80% of the initial discharge capacity after cycling for 2000 times at 20 C.

  6. 不同粒径单分散SiO2粒子的制备与表面改性%Preparation and Surface Modification of Monodispersed Silica Colloid Particles with Different Dimensions

    Institute of Scientific and Technical Information of China (English)

    刘文军; 罗鲲; 喻亮

    2012-01-01

    TEOS was employed to prepare SiO2 colloid particles in diameters of 290nm, 960nm, 1.3μm and 1.9 μm, respectively,by sol-gel and seed-mediated growth methods. The effect of KH570 treatment on the surface hydro-phobicity of the S1O2 colloid particles was investigated. The SiO2 colloid particles were characterized by particle size analysis, SEM and XRD, which indicate that the products are monodispersed spherical SiO2 particles. Measurements of contact angle, hydroxyl group number and lipophilic degree were also carried out to investigate the modification process, which reveal that the concentration of KH570 and modification time exert a significant effect on the hydro-phobicity of the as^modified S\\Ch colloid particles, where the addition of acetone into the KH570 ethanol solution is more beneficial than water for the surface modification, An ethanol solution containing 1% KH570 with addition of acetone and 6-hour reflux were determined as the optimized condition for the modification of SiO2 particles. The introduction of KH570 into the sol-gel process was able to prepare hydrophobic monodispersed SiO2 particles with a diameter of 1.9μm in one step.%以正硅酸乙酯为原料,采用溶胶-凝胶法及种子生长法制备出不同粒径(290nm、960nm、1.3μm和1.9μm)的SiO2胶体颗粒,并研究了KH570对SiO2胶体颗粒表面疏水性的影响.粒度分析、扫描电镜及X射线衍射分析结果表明,产物均为球形单分散SiO2胶体颗粒;而接触角、表面羟基数和亲油化度等测试结果显示,KH570浓度和改性时间对SiO2胶体表面性质影响显著,且丙酮作为助剂改性效果比水更好,最佳条件是以丙酮为助剂,使用1%KH570回流处理6h.此外,在存在KH570时进行溶胶-凝胶过程可一步制备出直径为1.9μm的单分散SiO2疏水颗粒.

  7. Artificial black opal fabricated from nanoporous carbon spheres.

    Science.gov (United States)

    Yamada, Yuri; Ishii, Masahiko; Nakamura, Tadashi; Yano, Kazuhisa

    2010-06-15

    A nanocasting method via chemical vapor deposition of acetonitrile was successfully employed to fabricate porous carbon colloidal crystal using colloidal crystal from monodispersed mesoporous silica spheres (MMSS) as a sacrificial scaffold. The mesostructure as well as periodic arrays within (111) plane of MMSS were replicated for the carbon colloidal crystal (black opal) with the length scale in the centimeter range. Brilliant iridescent colors were clearly observed for the first time on the black carbon colloidal crystal fabricated from porous carbon spheres, and they changed dramatically in accordance with the observation angle, like natural black opals. Reflection spectra measurements based on 2D surface diffraction and Bragg diffraction in the mirror mode were conducted for the fabricated carbon periodic arrays. The periodicity in the (111) plane as well as in the direction perpendicular to the (111) plane of the colloidal crystal was evaluated by comparing the results obtained from these two measurements. It was found that the periodicity in the direction perpendicular to the (111) surface is not high for the obtained black carbon opal. On the other hand, the relationship between the incident angles and the peak wavelengths of the reflection spectra, collected in the condition where the incident light and the reflected light pass through in the same direction, is governed by an approximation based on 2D surface diffraction. The results imply that the origin of the iridescent colors on the fabricated black carbon opal is derived from the periodicity not in the direction perpendicular to the (111) plane but within the (111) plane.

  8. Preparation and Properties of Monodisperse SnO2 Hollow Micro/Nano Spheres%单分散SnO2中空微纳米球的制备和性质

    Institute of Scientific and Technical Information of China (English)

    蔡宏敏; 任素贞; 王萌; 贾翠英

    2013-01-01

      模板法是制备无机中空微纳米球的重要方法之一。本文以苯乙烯为单体,通过乳液聚合得到粒径约为620 nm的单分散聚苯乙烯(PS)微球。以磺化后的聚苯乙烯(PSS)微球为模板,利用阴阳离子静电吸附作用,将PSS与前驱体SnSO4中的Sn2+结合。通过Sn2+在乙醇-水介质中的水解作用得到核-壳复合结构,再经高温煅烧,得到SnO2中空微纳米球。实验对前驱体的浓度、表面活性剂的用量、反应时间及模板选择等方面做了研究,通过扫描电镜(SEM)、X射线衍射(XRD)、红外(IR)光谱、热重分析(TGA)、H2程序升温还原(H2-TPR)、Brunauer-Emmett-Tel er (BET)比表面积等技术深入探究SnO2中空微纳米球的结构,并对比中空SnO2与实心粒子的氧化还原特性。 BET和H2-TPR显示将SnO2制备成微纳米空心球后其比表面积增大,表面氧空位明显增多,氧化活性明显提高。从IR及XRD推断核-壳结构形成机理,进而优化出简单合理的实验方案,获得表面光滑、结构致密,包覆厚度可控的SnO2中空微纳米球。%Templating is one of the most important methods for preparation of inorganic hol ow micro/nano spheres. We prepared monodisperse polystyrene (PS) microspheres having a diameter of 620 nm by the emulsion polymerization of styrene. Sulfonated polystyrene (PSS) microspheres were used as a template, through electrostatic adsorption of anions and cations, for modification with Sn2 + from SnSO4 precursor. The core-shel composite structures thereby produced through Sn2+ hydrolysis in an ethanol-water medium were calcined at high temperature to remove PSS and to obtain SnO2 hol ow micro/nano spheres. We investigated the effects of precursor concentration, amount of surfactant, reaction time, and templates choice. Scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetric analysis (TGA), H2 temperature programmed

  9. 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.

  10. Hydrothermal synthesis of monodisperse ZnxCd1-xS spheres and their photocatalytic properties%水热合成单分散球状ZnxCd1-xS及其光催化性质

    Institute of Scientific and Technical Information of China (English)

    贾志方; 王富民; 辛峰

    2011-01-01

    采用简单的水热合成路线制备高产量单分散球状ZnxCd1-xS,通过X射线衍射、扫描电镜以及紫外-可见漫反射对所得的产物进行表征.结果表明,所得产物呈现六方相纤锌矿结构,并且ZnxCd1-xS产物呈现出很好的均匀性与规则性.采用光催化降解罗丹明B反应来评价ZnxCd1-xS的光催化活性.其中,Zn0.4Cd0.6S具有最高的催化活性,并且在降解反应过程中表现出很高的稳定性.%Monodisperse ZnxCd1-xS spheres were successfully fabricated with a high yield by a facile hydrothermal route.The as-prepared samples were characterized by X-ray diffractometry,scanning electron microscopy and UV-vis diffusion reflectance spectroscopy.The results indicate that all the prepared samples have the same hexagonal wurtzite phase and exhibit good size uniformity and regularity.Degradation of rhodamine-B (RhB) was used to evaluate the photocatalytic activities of ZnxCd1-xS samples.Zn0.4Cd0.6S possessed the best photocatalytic activity and exhibited high stability during the reaction.

  11. Heterogeneous catalysts need not be so "heterogeneous": monodisperse Pt nanocrystals by combining shape-controlled synthesis and purification by colloidal recrystallization.

    Science.gov (United States)

    Kang, Yijin; Li, Meng; Cai, Yun; Cargnello, Matteo; Diaz, Rosa E; Gordon, Thomas R; Wieder, Noah L; Adzic, Radoslav R; Gorte, Raymond J; Stach, Eric A; Murray, Christopher B

    2013-02-20

    Well-defined surfaces of Pt have been extensively studied for various catalytic processes. However, industrial catalysts are mostly composed of fine particles (e.g., nanocrystals), due to the desire for a high surface to volume ratio. Therefore, it is very important to explore and understand the catalytic processes both at nanoscale and on extended surfaces. In this report, a general synthetic method is described to prepare Pt nanocrystals with various morphologies. The synthesized Pt nanocrystals are further purified by exploiting the "self-cleaning" effect which results from the "colloidal recrystallization" of Pt supercrystals. The resulting high-purity nanocrystals enable the direct comparison of the reactivity of the {111} and {100} facets for important catalytic reactions. With these high-purity Pt nanocrystals, we have made several observations: Pt octahedra show higher poisoning tolerance in the electrooxidation of formic acid than Pt cubes; the oxidation of CO on Pt nanocrystals is structure insensitive when the partial pressure ratio p(O2)/p(CO) is close to or less than 0.5, while it is structure sensitive in the O(2)-rich environment; Pt octahedra have a lower activation energy than Pt cubes when catalyzing the electron transfer reaction between hexacyanoferrate (III) and thiosulfate ions. Through electrocatalysis, gas-phase-catalysis of CO oxidation, and a liquid-phase-catalysis of electron transfer reaction, we demonstrate that high quality Pt nanocrystals which have {111} and {100} facets selectively expose are ideal model materials to study catalysis at nanoscale.

  12. Real-Time Fluorescence Detection in Aqueous Systems by Combined and Enhanced Photonic and Surface Effects in Patterned Hollow Sphere Colloidal Photonic Crystals.

    Science.gov (United States)

    Zhong, Kuo; Wang, Ling; Li, Jiaqi; Van Cleuvenbergen, Stijn; Bartic, Carmen; Song, Kai; Clays, Koen

    2017-05-16

    Hollow sphere colloidal photonic crystals (HSCPCs) exhibit the ability to maintain a high refractive index contrast after infiltration of water, leading to extremely high-quality photonic band gap effects, even in an aqueous (physiological) environment. Superhydrophilic pinning centers in a superhydrophobic environment can be used to strongly confine and concentrate water-soluble analytes. We report a strategy to realize real-time ultrasensitive fluorescence detection in patterned HSCPCs based on strongly enhanced fluorescence due to the photonic band-edge effect combined with wettability differentiation in the superhydrophobic/superhydrophilic pattern. The orthogonal nature of the two strategies allows for a multiplicative effect, resulting in an increase of two orders of magnitude in fluorescence.

  13. Monodisperse Silver Nanoparticles Synthesized by a Microwave-Assisted Method

    Institute of Scientific and Technical Information of China (English)

    ZHU Shao-Peng; TANG Shao-Chun; MENG Xiang-Kang

    2009-01-01

    Silver nanoparticles with an average size of about 2Onto are synthesized in a colloidal solution with the aid of microwave irradiation. Neither additional reductant nor stabilizer is required in this microwave-assisted method.The color of the colloidal solution is found to be dark green, different from the characteristic yellow of silver colloidal solutions. The silver nanoparticles in the colloidal solution have a narrow size distribution and large yield quantity. UV-visible absorption spectroscopy analysis reveals that the as-synthesized monodisperse silver nanoparticles have exceptional optical properties. Raman spectroscopy measurements demonstrate that these silver nanoparticles exhibit a notable surface-enhanced Raman scattering ability.

  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. Water evaporation in silica colloidal deposits.

    Science.gov (United States)

    Peixinho, Jorge; Lefèvre, Grégory; Coudert, François-Xavier; Hurisse, Olivier

    2013-10-15

    The results of an experimental study on the evaporation and boiling of water confined in the pores of deposits made of mono-dispersed silica colloidal micro-spheres are reported. The deposits are studied using scanning electron microscopy, adsorption of nitrogen, and adsorption of water through attenuated total reflection-infrared spectroscopy. The evaporation is characterized using differential scanning calorimetry and thermal gravimetric analysis. Optical microscopy is used to observe the patterns on the deposits after evaporation. When heating at a constant rate and above boiling temperature, the release of water out of the deposits is a two step process. The first step is due to the evaporation and boiling of the surrounding and bulk water and the second is due to the desorption of water from the pores. Additional experiments on the evaporation of water from membranes having cylindrical pores and of heptane from silica deposits suggest that the second step is due to the morphology of the deposits.

  16. A Global Investigation About Hard Core Attractive Yukawa Approximation and Adhesive Hard Sphere Approximation for Structure of Colloidal Dispersion Systems

    Institute of Scientific and Technical Information of China (English)

    ZHOU Shi-Qi

    2005-01-01

    The accuracy of hard core attractive Yukawa (HCAY) potential and adhesive hard sphere (AH) potential in representing the structure factor of short range square well potential and Asakura and Oosawa (AO) depletion potential is examined by comparing theoretical predictions with the existing simulation data and the present numerical results from the non-linear optimized random phase approximation closure for Ornstein-Zernike equation. For the case of square-well (SW) potential, it is shown that the structure factor of HCAY potential based on a recently proposed semi-analytical expression for the radial distribution function can describe the structure factor of SW potential with reduced well width λ≤ 2 only if the reduced contact potential βesw ≤ 0.25, while the analytical expression for the structure factor of AH potential under Percus-Yevick (PY) approximation completely fails for the case of λ> 1.2. For the case of AO depletion potential, the domain of validity of both HCAY potential and AH potential is complementary. With the above analysis and considering the solid-liquid transition of the AH potential with an adhesive parameter τ below 1.31 cannot be predicted by modified weighted density approximation, the role played by the HCAY potential about the mapping manipulation should not be ignored.

  17. 3D investigation on polystyrene colloidal crystals by floatage self-assembly with mixed solvent via synchrotron radiation x-ray phase-contrast computed tomography

    Science.gov (United States)

    Fu, Yanan; Xie, Honglan; Deng, Biao; Du, Guohao; Xiao, Tiqiao

    2017-06-01

    The floatage self-assembly method was introduced with mixed solvent as the medium of polystyrene sphere suspension to fabricate the colloidal crystal. The three dimensional (3D) void system of the colloidal crystal was noninvasively characterized by synchrotron radiation phase-contrast computed tomography, and the quantitative image analysis was implemented aiming to the polystyrene sphere colloidal crystal. Comparing with gravity sedimentation method, the three samples fabricated from floatage self-assembly with mixed solvents have the lowest porosity, and when ethylene glycol and water were mixed with ratio of 1:1, the lowest porosity of 27.49% could be achieved, that has been very close to the minimum porosity of ordered 3D monodisperse sphere array (26%). In single slices, the porosities and fractal dimension for the voids were calculated. The results showed that two factors would significantly influence the porosity of the whole colloidal crystal: the first deposited sphere layer's orderliness and the sedimentation speed of the spheres. The floatage self-assembly could induce a stable close-packing process, resulted from the powerful nucleation force-lateral capillary force coupled with the mixed solvent to regulate the floating upward speed for purpose of matching the assembly rate.

  18. Synthesis of porous carbon balls from spherical colloidal crystal templates.

    Science.gov (United States)

    Kim, Youngchan; Cho, Chang-Yeol; Kang, Ji-Hwan; Cho, Young-Sang; Moon, Jun Hyuk

    2012-07-17

    Spherical inverse opal (IO) porous carbon was produced utilizing silica colloidal crystal spheres as templates. The spherical colloidal crystals were obtained through the self-assembly of monodisperse particles inside an emulsion droplet with confined geometry. The templates were inverted using a carbon precursor, phenol-formaldehyde (PF) resol. We demonstrated a two-step synthesis involving the subsequent infiltration of the PF resol precursor into the spherical colloidal crystal template and a one-step synthesis using a silica colloidal solution containing dissolved PF resol. In the former case, the sizes of the IO carbon balls were controlled by the size of the colloidal crystal templates, and diameters of a few micrometers up to 50 μm were obtained. The average diameter of the macropores created by the silica particles was 230 nm. Moreover, meso-/macroporous IO carbon balls were created using block-copolymer templates in the PF resol. In the one-step synthesis, the concentration of PF resol in the colloidal solution controlled the diameter of the IO carbon balls. IO balls smaller than 3 μm were obtained from the direct addition of 5% PF resol. The one-step synthesis produced rather irregular porous structures reflecting the less ordered crystallization processes inside the spherical colloidal crystals. Nitrogen adsorption and cyclic voltammetry measurements were conducted to measure the specific area and electroactive surface area of the IO carbon balls. The specific area of the mesopores-incorporated IO carbon balls was 1.3 times higher than that of bare IO carbon balls. Accordingly, the meso-/macroporous porous carbon balls exhibited higher electrocatalytic properties than the macroporous carbon balls.

  19. Nucleation and crystal growth in a suspension of charged colloidal silica spheres with bi-modal size distribution studied by time-resolved ultra-small-angle X-ray scattering.

    Science.gov (United States)

    Hornfeck, Wolfgang; Menke, Dirk; Forthaus, Martin; Subatzus, Sebastian; Franke, Markus; Schöpe, Hans-Joachim; Palberg, Thomas; Perlich, Jan; Herlach, Dieter

    2014-12-07

    A suspension of charged colloidal silica spheres exhibiting a bi-modal size distribution of particles, thereby mimicking a binary mixture, was studied using time-resolved ultra-small-angle synchrotron X-ray scattering (USAXS). The sample, consisting of particles of diameters d(A) = (104.7 ± 9.0) nm and d(B) = (88.1 ± 7.8) nm (d(A)/d(B) ≈ 1.2), and with an estimated composition A(0.6(1))B(0.4(1)), was studied with respect to its phase behaviour in dependance of particle number density and interaction, of which the latter was modulated by varying amounts of added base (NaOH). Moreover, its short-range order in the fluid state and its eventual solidification into a long-range ordered colloidal crystal were observed in situ, allowing the measurement of the associated kinetics of nucleation and crystal growth. Key parameters of the nucleation kinetics such as crystallinity, crystallite number density, and nucleation rate density were extracted from the time-resolved scattering curves. By this means an estimate on the interfacial energy for the interface between the icosahedral short-range ordered fluid and a body-centered cubic colloidal crystal was obtained, comparable to previously determined values for single-component colloidal systems.

  20. Glass-liquid-glass reentrance in mono-component colloidal dispersions

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez-Gonzalez, P E; Medina-Noyola, M [Instituto de Fisica ' Manuel Sandoval Vallarta' , Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, 78000 San Luis Potosi, SLP (Mexico); Vizcarra-Rendon, A [Unidad Academica de Fisica, Universidad Autonoma de Zacatecas, Paseo la Bufa y Calzada Solidaridad, 98600, Zacatecas, Zac. (Mexico); Guevara-Rodriguez, F de J [Coordinacion de IngenierIa Molecular, Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152, 07730 Mexico, DF (Mexico)

    2008-05-21

    The self-consistent generalized Langevin equation (SCGLE) theory of colloid dynamics is employed to describe the ergodic-non-ergodic transition in model mono-disperse colloidal dispersions whose particles interact through hard-sphere plus short-ranged attractive forces. The ergodic-non-ergodic phase diagram in the temperature-concentration state space is determined for the hard-sphere plus attractive Yukawa model within the mean spherical approximation for the static structure factor by solving a remarkably simple equation for the localization length of the colloidal particles. Finite real values of this property signals non-ergodicity and determines the non-ergodic parameters f(k) and f{sub s}(k). The resulting phase diagram for this system, which involves the existence of reentrant (repulsive and attractive) glass states, is compared with the corresponding prediction of mode coupling theory. Although both theories coincide in the general features of this phase diagram, there are also clear qualitative differences. One of the most relevant is the SCGLE prediction that the ergodic-attractive glass transition does not preempt the gas-liquid phase transition, but always intersects the corresponding spinodal curve on its high-concentration side. We also calculate the ergodic-non-ergodic phase diagram for the sticky hard-sphere model to illustrate the dependence of the predicted SCGLE dynamic phase diagram on the choice of one important constituent element of the SCGLE theory.

  1. Facile preparation of ZIF-8@Pd-CSS sandwich-type microspheres via in situ growth of ZIF-8 shells over Pd-loaded colloidal carbon spheres with aggregation-resistant and leach-proof properties for the Pd nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Tong; Lin, Lu [State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, 116024 (China); Zhang, Xiongfu, E-mail: xfzhang@dlut.edu.cn [State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, 116024 (China); Liu, Haiou; Yan, Xinjuan [State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, 116024 (China); Liu, Zhang; Yeung, King Lun [Department of Chemical and Biomolecular Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR (China)

    2015-10-01

    Graphical abstract: - Highlights: • Uniform-sized colloidal carbon spheres were synthesized from low-cost glucose. • Pd nanoparticles were loaded onto the carbon spheres via self-reduction method. • A layer of ZIF-8 shell was in situ grown over the Pd-loaded carbon spheres. • The ZIF-8@Pd-CCS showed leach-proof and aggregation-resistant properties of Pd. - Abstract: Aiming to enhance the stability of noble metal nanoparticles that are anchored on the surface of colloidal carbon spheres (CCSs), we designed and prepared a new kind of sandwich-structured ZIF-8@Pd-CCS microsphere. Typically, uniform CCSs were first synthesized by the aromatization and carbonization of glucose under hydrothermal conditions. Subsequently, noble metal nanoparticles, herein Pd nanoparticles, were attached to the surface of CCSs via self-reduction route, followed by in situ assembly of a thin layer of ZIF-8 over the Pd nanoparticles to form the sandwich-type ZIF-8@Pd-CCS microspheres. X-ray diffraction (XRD) patterns and Fourier transform infrared spectroscopy (FTIR) spectra confirmed the presence of crystalline ZIF-8, while TEM analysis revealed that the ZIF-8 shells were closely bound to the Pd-loaded CCSs. The shell thickness could be tuned by varying the ZIF-8 assembly cycles. Further, liquid-phase hydrogenation of 1-hexene as the probe reaction was carried out over the ZIF-8@Pd-CCS microspheres and results showed that the prepared microspheres exhibited excellent agglomeration-resistant and leach-proof properties for the Pd nanoparticles, thus leading to the good reusability of the ZIF-8@Pd-CCS microspheres.

  2. Engineered monodisperse mesoporous materials

    Energy Technology Data Exchange (ETDEWEB)

    Saunders, R.S.; Small, J.H.; Lagasse, R.R.; Schroeder, J.L.; Jamison, G.M.

    1997-08-01

    Porous materials technology has developed products with a wide variety of pore sizes ranging from 1 angstrom to 100`s of microns and beyond. Beyond 15{angstrom} it becomes difficult to obtain well ordered, monodisperse pores. In this report the authors describe efforts in making novel porous material having monodisperse, controllable pore sizes spanning the mesoporous range (20--500 {angstrom}). They set forth to achieve this by using unique properties associated with block copolymers--two linear homopolymers attached at their ends. Block copolymers phase separate into monodisperse mesophases. They desired to selectively remove one of the phases and leave the other behind, giving the uniform monodisperse pores. To try to achieve this the authors used ring-opening metathesis polymerization to make the block copolymers. They synthesized a wide variety of monomers and surveyed their polymers by TGA, with the idea that one phase could be made thermally labile while the other phase would be thermally stable. In the precipitated and sol-gel processed materials, they determined by porosimetry measurements that micropores, mesopores, and macropores were created. In the film processed sample there was not much porosity present. They moved to a new system that required much lower thermal treatments to thermally remove over 90% of the labile phase. Film casting followed by thermal treatment and solvent extraction produced the desired monodisperse materials (based solely on SEM results). Modeling using Density Functional Theory was also incorporated into this project. The modeling was able to predict accurately the domain size and spacing vs. molecular weight for a model system, as well as accurate interfacial thicknesses.

  3. Preparation and modification of SiO2 colloidal spheres and it' s self - assembly%二氧化硅胶体球的制备、改性及其胶体晶体的组装

    Institute of Scientific and Technical Information of China (English)

    伍媛婷; 王秀峰

    2011-01-01

    Monodisperse SiO2 particles were synthesized by StOber method. The SiO2 particles were moddied by butanedioic acid. And SiO2 colloidal crystal was fabricated by the vertical deposition method.The crystal formation, micromorphology and electrical properties were characterized by X -ray diffraction (XRD), Scanning electron microscope (SEM) and Zeta potential instrument. The results show that the SiO2 particles are monodisperse non - crystalline solid particles with the particle size in 150 ~ 360nm. Zeta potential instrument indicates that the zeta potentials of the SiO2 specimens with different particle sizes reach the maximum values when the modified amount of butanedioic acid is 1.5g in the 50mL acetonitrile solvents. And the colloidal crystal prepared by modified SiO2 microspheres has more ordered structure.%采用改进的St(O)ber法制备了单分散性较好、表面光滑的SiO2球形颗粒,将丁二酸化学键合于SiO2胶体球表面以提高其Zeta电势,再采用垂直沉积法在水溶液中制备出SiO2胶体晶体.通过X射线衍射仪、场发射扫描电子显微镜(SEM)和Zeta电位粒度仪对颗粒和胶体晶体的晶型、显微形貌、电学性能进行测试分析.结果表明:所得SiO2颗粒为无定形态,SiO2颗粒均为完整的球形颗粒,粒径在150~360nm范围内;不同粒径SiO2颗粒经丁二酸改性后Zeta电势均出现极大值,且改性后的SiO2微球组装的胶体晶体排列紧密有序,呈现密堆垛结构.

  4. 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.

  5. DNA- and AC electric field-assisted assembly of two-dimensional colloidal photonic crystals and their controlled defect insertion

    Science.gov (United States)

    Kim, Sejong

    Photonic crystals (PC) are structures in which the refractive index is a periodic function in space. The ability of photonic crystals to localize and manipulate electromagnetic waves has attracted considerable attention from the scientific community. The self-assembly of monodisperse micrometer scale colloidal spheres into hexagonal closed-packed colloidal crystals provides a simple, fast, and cheap materials chemistry approach to PCs. Employing DNA supramolecular recognition, 2-dimensional (2D) photonic crystal monolayer was fabricated with monodisperse polystyrene colloidal microspheres. Amine-terminated DNA oligomers were covalently attached onto carboxy-decorated microspheres and enabled their DNA-functionalization while preserving their colloidal stability and organization properties. Following a capillary-force-assisted organization of DNA-decorated microspheres into close-packed 2D opaline arrays, the first monolayer was immobilized by DNA hybridization. Insertion of vacancies at predetermined sites within the lattice of colloidal crystals is a prerequisite in order to realize high-quality, opaline-based photonic devices. The previously obtained DNA-hybridization type binding of 2D-opaline arrays provides a heat-sensitive "adhesive" between substrate and microspheres within a surrounding aqueous medium that enables tuning the hybridization strength of DNA linker as well as a mechanism to facilitate the removal of unbound microspheres. Focusing a laser beam onto a single microsphere of the opaline array induces localized heating that enables the microsphere to detach, leaving behind vacancies. By repeating this process, line vacancies were successfully obtained. The effects of salt concentration, laser power, light-absorbing dyes, DNA length and refractive index mismatch were investigated and found to correlate with heat-induced DNA dehybridization. In addition, AC (alternating current) electrokinetic force was also utilized to obtain assembly of colloidal

  6. Experimental determination of particle size distributions in colloidal systems by dynamic light scattering. Application to polystyrene latex spheres and to nonionic microemulsions

    NARCIS (Netherlands)

    Eshuis, A.; Harbers, G.; Doornink, D.J.; Mijnlieff, P.F.

    1985-01-01

    Information about polydisperse colloidal systems was obtained by dynamic light scattering. The correlation functions obtained were analyzed by the histogram method and the method of cumulants. The former was, as a test, applied to a nearly monodispere polystyrene latex. The agreement between the

  7. Preparation of Monodisperse Nanoparticle of Layered Double Hydroxides and Polyoxyethylene Sulfate

    Institute of Scientific and Technical Information of China (English)

    XU Huizhong; QIN Lianjie; ZHANG Hong; YANG Qinzheng; YANG Jing

    2005-01-01

    In order to obtain the bio-molecule/ LDHs nanocomposites having regular crystal structure,three nanocomposites of layered double hydroxides and polyoxyethylene sulfates were prepared by ion-exchange method. TEM analysis reveals that the monodisperse rigid .sphere of approximately 200 nm in diameter could be gotten when the intergallery anion was PEGS-400. Such monodisperse nanoparticle could be used as a promising precursor for preparing bio-molecule/LDHs nanocomposites.

  8. Preparation of large monodisperse vesicles.

    Directory of Open Access Journals (Sweden)

    Ting F Zhu

    Full Text Available Preparation of monodisperse vesicles is important both for research purposes and for practical applications. While the extrusion of vesicles through small pores (approximately 100 nm in diameter results in relatively uniform populations of vesicles, extrusion to larger sizes results in very heterogeneous populations of vesicles. Here we report a simple method for preparing large monodisperse multilamellar vesicles through a combination of extrusion and large-pore dialysis. For example, extrusion of polydisperse vesicles through 5-microm-diameter pores eliminates vesicles larger than 5 microm in diameter. Dialysis of extruded vesicles against 3-microm-pore-size polycarbonate membranes eliminates vesicles smaller than 3 microm in diameter, leaving behind a population of monodisperse vesicles with a mean diameter of approximately 4 microm. The simplicity of this method makes it an effective tool for laboratory vesicle preparation with potential applications in preparing large monodisperse liposomes for drug delivery.

  9. Particle and substrate charge effects on colloidal self-assembly in a sessile drop.

    Science.gov (United States)

    Yan, Qingfeng; Gao, Li; Sharma, Vyom; Chiang, Yet-Ming; Wong, C C

    2008-10-21

    By direct video monitoring of dynamic colloidal self-assembly during solvent evaporation in a sessile drop, we investigated the effect of surface charge on the ordering of colloidal spheres. The in situ observations revealed that the interaction between charged colloidal spheres and substrates affects the mobility of colloidal spheres during convective self-assembly, playing an important role in the colloidal crystal growth process. Both ordered and disordered growth was observed depending on different chemical conditions mediated by surface charge and surfactant additions to the sessile drop system. These different self-assembly behaviors were explained by the Coulombic and hydrophobic interactions between surface-charged colloidal spheres and substrates.

  10. Particle cage dynamics in flowing colloidal dispersions

    Science.gov (United States)

    Marenne, Stephanie; Morris, Jeffrey F.

    2016-11-01

    The idea of the particle in a suspension at rest being trapped in a cage formed by its neighbors, widely used to understand glassy suspensions, has been applied to freely flowing suspensions. Stokesian Dynamics, a discrete particle simulation, is used to simulate the flow of monodisperse colloidal hard sphere suspensions. The cage analogy is useful to study the nonlinear stress in the material during start-up of shear flow, where the neighbor cage deforms and breaks, and during oscillatory shear flow where, depending on the amplitude of oscillation, the particle is trapped inside the cage or escapes during the oscillation cycle. A precise statistical definition of the cage in terms of the nearest neighbor ring in the pair distribution function is developed. We examine the dependence of the cage dynamics on the volume fraction of particles and the Peclet number Pe , the ratio between shear and Brownian forces. Under flow, the cage is found to break at quite definite positions, and the structural distortion is found to be clearly related to the shear and normal stress response. The shear strain needed to break the neighbor cage depends on Pe as Brownian motion enhances the total deformation. A simple model captures the strain at the stress overshoot for start-up of steady shear.

  11. Preparation of Monodisperse Core-Shell Type Silver-coated Silica Composite-spheres and its Mechanism%单分散核-壳型银包覆二氧化硅微球的制备及复合机理研究

    Institute of Scientific and Technical Information of China (English)

    洪阳; 诸跃进

    2015-01-01

    The synthesis of bare silica is achieved based on Stober method and the synthesis of SiO2@Ag has been obtained by controlled-reduction of silver nitrate and ammonia in ethyl alcohol with PVP as a protective and reducing agent. The particles size, structure and composition analyses reveal that the resultant SiO2@Ag composite-spheres are monodisperse which is well-proportioned and stable with a mean silica core diameter of 255 nm and the silver shell nanoparticles diameter of 8 nm. The synthesis mechanism of the core-shell type composite-spheres is studied in terms of the impact on growth and morphology from these the main factors that are silver source solution, reaction temperature and pH of the reaction solution. The optimal synthesis conditions are finally obtained as follows: the optimum ion concentration is about 2.0 mmol·L-1, the main growth temperature is 40~50℃, and the best core-shell structure appears in pH=12.12.%基于Stober水解法制备得到纯二氧化硅微球,通过以PVP为保护剂和还原剂的可控还原法制备得到银包覆二氧化硅复合微球.该复合微球的单分散性好,且均匀而稳定,其中核的平均粒径在255 nm,壳层银纳米粒子粒径约为8 nm.根据银源溶液的浓度、反应温度以及反应液pH值等3个主要因素对复合微球的生长和形貌的重要影响,研究了该核-壳型复合微球的合成机理,得到最优合成条件:最佳离子浓度为2.0 mmol·L-1,主要生长温度为40~50℃,且最适酸碱度在pH=12.12处.该复合微球在光学和催化等诸多领域都有广泛的潜在应用前景.

  12. 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

  13. 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)

  14. 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.

  15. A Facile Solvothermal Synthesis of Monodisperse Ni Nanoparticles

    Institute of Scientific and Technical Information of China (English)

    YU Peng-fei; CUI Bin; ZHANG Yan; SHI Qi-zhen

    2008-01-01

    A simple solvothermal approach was developed to synthesize uniform spherical monodisperse Ni nanoparticles, which can easily disperse in nonpolar solvents to form homogenous colloidal solution. The as-prepared sample was characterized by XRD, TEM, and FTIR. The results indicate that Ni nanoparticles have the structure of face-centered cube and a narrow distribution with a diameter of (3.5±0.5) nm. The FTIR spectrum reveals that the as a surfactant. The probable formation mechanism of the spherical nanoparticles was also discussed.

  16. 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

  17. Recent advances in fabrication of monolayer colloidal crystals and their inverse replicas

    Institute of Scientific and Technical Information of China (English)

    YE XiaoZhou; QI LiMin

    2014-01-01

    Monolayer colloidal crystals(MCCs)are two-dimensional(2D)colloidal crystals consisting of a monolayer of monodisperse colloidal particles arrayed with a 2D periodic order.In recent years,MCCs have attracted intensive interest because they can act as 2D photonic crystals and be used as versatile templates for fabrication of various 2D nanostructure arrays.In this review,we provide an overview of the recent progress in the controllable fabrication of MCCs and their inverse replicas.First,some newly-developed methods for the self-assembly of MCCs based on different strategies including interfacial assembly and convective assembly are introduced.Second,some representative novel methods regarding the fabrication of various functional2D inverse replicas of MCCs,such as 2D arrays of nanobowls,nanocaps,and hollow spheres,as well as 2D monolayer inverse opals(MIOs),are described.In addition,the potential applications of MCCs and their inverse replicas are discussed.

  18. 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

  19. Routh's sphere

    NARCIS (Netherlands)

    Cushman, R.

    2001-01-01

    In this paper we show that the integral map of Rouths sphere has monodromy when the sphere becomes gyroscopically unstable This uses the nonHamiltonian monodromy of Rouths sphere has center of mass not at its geometrical center and moment of inertia tensor with two equal principal moments of inerti

  20. 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.

  1. 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

  2. A general method to coat colloidal particles with titiana

    NARCIS (Netherlands)

    Demirors, A.F.; van Blaaderen, A.; Imhof, A.

    2010-01-01

    We describe a general one-pot method for coating colloidal particles with amorphous titania. Various colloidal particles such as silica particles, large silver colloids, gibbsite platelets, and polystyrene spheres were successfully coated with a titania shell. Although there are several ways of coat

  3. Colloidal dynamics in flow and confinement

    NARCIS (Netherlands)

    Ghosh, Somnath

    2015-01-01

    The aim of this thesis is to understand how the diffusive dynamics and flow behaviors of colloidal hard spheres are influenced by the confinement of nearby walls. The Brownian motion of hard spheres in quiescent bulk fluids is well known, but the presence of confining walls generate new physical phe

  4. A facile method to produce highly monodispersed nanospheres of cystine aggregates

    Science.gov (United States)

    Han, Hongliang; Wang, Chungang; Ma, Zhanfang; Su, Zhongmin

    2006-10-01

    Multiple shapes of nano- and micro-structured cystine aggregates, including spheres, rods, spindles, dendrites, and multipods, were easily synthesized just by adjusting the concentrations and pH values of L-Cysteine solutions under ultrasonic irritation. Importantly, highly monodispersed nanospheres of cystine aggregates 225 nm in diameter without any other shapes were easily obtained for the system of 0.1 M L-Cysteine with pH 8. This will provide a very simple and effective approach to produce monodispersed cystine microspheres, which could promote new possibilities for future applications in biosensor, drug delivery, medicine, and the production of nanomaterials.

  5. A facile method to produce highly monodispersed nanospheres of cystine aggregates

    Energy Technology Data Exchange (ETDEWEB)

    Han Hongliang; Wang Chungang; Ma Zhanfang; Su Zhongmin [Chemistry Department, Northeast Normal University, Changchun 130024 (China)

    2006-10-28

    Multiple shapes of nano- and micro-structured cystine aggregates, including spheres, rods, spindles, dendrites, and multipods, were easily synthesized just by adjusting the concentrations and pH values of L-Cysteine solutions under ultrasonic irritation. Importantly, highly monodispersed nanospheres of cystine aggregates 225 nm in diameter without any other shapes were easily obtained for the system of 0.1 M L-Cysteine with pH 8. This will provide a very simple and effective approach to produce monodispersed cystine microspheres, which could promote new possibilities for future applications in biosensor, drug delivery, medicine, and the production of nanomaterials.

  6. Equilibrium fluid-crystal interfacial free energy of bcc-crystallizing aqueous suspensions of polydisperse charged spheres.

    Science.gov (United States)

    Palberg, Thomas; Wette, Patrick; Herlach, Dieter M

    2016-02-01

    The interfacial free energy is a central quantity in crystallization from the metastable melt. In suspensions of charged colloidal spheres, nucleation and growth kinetics can be accurately measured from optical experiments. In previous work, from these data effective nonequilibrium values for the interfacial free energy between the emerging bcc nuclei and the adjacent melt in dependence on the chemical potential difference between melt phase and crystal phase were derived using classical nucleation theory (CNT). A strictly linear increase of the interfacial free energy was observed as a function of increased metastability. Here, we further analyze these data for five aqueous suspensions of charged spheres and one binary mixture. We utilize a simple extrapolation scheme and interpret our findings in view of Turnbull's empirical rule. This enables us to present the first systematic experimental estimates for a reduced interfacial free energy, σ(0,bcc), between the bcc-crystal phase and the coexisting equilibrium fluid. Values obtained for σ(0,bcc) are on the order of a few k(B)T. Their values are not correlated to any of the electrostatic interaction parameters but rather show a systematic decrease with increasing size polydispersity and a lower value for the mixture as compared to the pure components. At the same time, σ(0) also shows an approximately linear correlation to the entropy of freezing. The equilibrium interfacial free energy of strictly monodisperse charged spheres may therefore be still greater.

  7. DEPLETION POTENTIAL OF COLLOIDS:A DIRECT SIMULATION STUDY

    Institute of Scientific and Technical Information of China (English)

    李卫华; 薛松; 马红孺

    2001-01-01

    The depletion interaction between abig sphere and a hard wall and between two big hard spheres in a hard sphere colloidal sytem was studied by the Monte Carlo method.Direct simulation of free energy difference was performed by means of the Acceptance Ratio Method (ARM).

  8. Aerosol-Assisted Synthesis of Monodisperse Single-Crystalline α-Cristobalite Nanospheres

    OpenAIRE

    Jiang, Xingmao; Bao, Lihong; Cheng, Yung-Sung; Dunphy, Darren R.; Li, Xiaodong; Brinker, C. Jeffrey

    2011-01-01

    Monodisperse single-crystalline α-cristobalite nanospheres have been synthesized by hydrocarbon-pyrolysis-induced carbon deposition on amorphous silica aerosol nanoparticles, devitrification of the coated silica at high temperature, and subsequent carbon removal by oxidation. The nanosphere size can be well controlled by tuning the size of the colloidal silica precursor. Uniform, high-purity nanocrystalline α-cristobalite is important for catalysis, nanocomposites, advanced polishing, and und...

  9. Order-to-Disorder Transition in Ring-Shaped Colloidal Stains

    NARCIS (Netherlands)

    Marin, Alvaro G.; Gelderblom, Hanneke; Lohse, Detlef; Snoeijer, Jacco H.

    2011-01-01

    A colloidal dispersion droplet evaporating from a surface, such as a drying coffee drop, leaves a distinct ring-shaped stain. Although this mechanism is frequently used for particle self-assembly, the conditions for crystallization have remained unclear. Our experiments with monodisperse colloidal p

  10. Aerosol fabrication methods for monodisperse nanoparticles

    Science.gov (United States)

    Jiang, Xingmao; Brinker, C Jeffrey

    2014-10-21

    Exemplary embodiments provide materials and methods for forming monodisperse particles. In one embodiment, the monodisperse particles can be formed by first spraying a nanoparticle-containing dispersion into aerosol droplets and then heating the aerosol droplets in the presence of a shell precursor to form core-shell particles. By removing either the shell layer or the nanoparticle core of the core-shell particles, monodisperse nanoparticles can be formed.

  11. Short-time diffusion in concentrated bidisperse hard-sphere suspensions.

    Science.gov (United States)

    Wang, Mu; Heinen, Marco; Brady, John F

    2015-02-14

    Diffusion in bidisperse Brownian hard-sphere suspensions is studied by Stokesian Dynamics (SD) computer simulations and a semi-analytical theoretical scheme for colloidal short-time dynamics, based on Beenakker and Mazur's method [Physica A 120, 388-410 (1983); 126, 349-370 (1984)]. Two species of hard spheres are suspended in an overdamped viscous solvent that mediates the salient hydrodynamic interactions among all particles. In a comprehensive parameter scan that covers various packing fractions and suspension compositions, we employ numerically accurate SD simulations to compute the initial diffusive relaxation of density modulations at the Brownian time scale, quantified by the partial hydrodynamic functions. A revised version of Beenakker and Mazur's δγ-scheme for monodisperse suspensions is found to exhibit surprisingly good accuracy, when simple rescaling laws are invoked in its application to mixtures. The so-modified δγ scheme predicts hydrodynamic functions in very good agreement with our SD simulation results, for all densities from the very dilute limit up to packing fractions as high as 40%.

  12. Dynamic arrest within the self-consistent generalized Langevin equation of colloid dynamics.

    Science.gov (United States)

    Yeomans-Reyna, L; Chávez-Rojo, M A; Ramírez-González, P E; Juárez-Maldonado, R; Chávez-Páez, M; Medina-Noyola, M

    2007-10-01

    This paper presents a recently developed theory of colloid dynamics as an alternative approach to the description of phenomena of dynamic arrest in monodisperse colloidal systems. Such theory, referred to as the self-consistent generalized Langevin equation (SCGLE) theory, was devised to describe the tracer and collective diffusion properties of colloidal dispersions in the short- and intermediate-time regimes. Its self-consistent character, however, introduces a nonlinear dynamic feedback, leading to the prediction of dynamic arrest in these systems, similar to that exhibited by the well-established mode coupling theory of the ideal glass transition. The full numerical solution of this self-consistent theory provides in principle a route to the location of the fluid-glass transition in the space of macroscopic parameters of the system, given the interparticle forces (i.e., a nonequilibrium analog of the statistical-thermodynamic prediction of an equilibrium phase diagram). In this paper we focus on the derivation from the same self-consistent theory of the more straightforward route to the location of the fluid-glass transition boundary, consisting of the equation for the nonergodic parameters, whose nonzero values are the signature of the glass state. This allows us to decide if a system, at given macroscopic conditions, is in an ergodic or in a dynamically arrested state, given the microscopic interactions, which enter only through the static structure factor. We present a selection of results that illustrate the concrete application of our theory to model colloidal systems. This involves the comparison of the predictions of our theory with available experimental data for the nonergodic parameters of model dispersions with hard-sphere and with screened Coulomb interactions.

  13. Preparation and antibacterial activities of hollow silica-Ag spheres.

    Science.gov (United States)

    Lin, Lin; Zhang, Haifang; Cui, Haiying; Xu, Mingqiang; Cao, Shunsheng; Zheng, Guanghong; Dong, Mingdong

    2013-01-01

    Hollow silica spheres with round mesoporous shells were synthesized by core-shell template method, using monodispersed cationic polystyrene particles as core, and TEOS (tetraethoxysilane) as the silica source to form shell. After calcination at 550°C, uniform spheres with a thin shell of silica and hollow interior structures. Transmission electron microscopy results showed that the size of the spheres is about 700 nm in diameter with narrow distribution. In addition, the spheres have a high surface area of 183 m(2)/g. The spheres were subsequently used as silver-loading substrates and the silver loaded spheres were tested in antimicrobial study against gram negative bacteria Eschrichia coli in vitro. The hollow silica-Ag spheres proved significantly higher antibacterial efficacy against E. coli as compared to that of the common silica-Ag particles.

  14. Three-dimensional Ordered Silica Colloidal Film Self-assembly Deposited on a Vertical Substrate

    Institute of Scientific and Technical Information of China (English)

    刘丽霞; 董鹏; 王晓冬; 程丙英

    2003-01-01

    A method for preparation of particle crystal film constructed trom monodisperse silica colloidal partices in diameter of about 300 nm is reported. The films were prepared from an ethanol suspension by vertical deposition that relies on capillary forces to assemble colloidal crystal particles on a vertical substrate. The 3D ordered films were characterized by transmission spectra and scanning electric microscope (SEM). The effect of evaporation temperature, particle concentration and sintered temperature on the quality of colloidal particle crystal film was investigated.

  15. Structure and Hydration of Highly Branched, Monodisperse Phytoglycogen Nanoparticles

    Science.gov (United States)

    Atkinson, John; Nickels, Jonathan; Stanley, Christopher; Diallo, Souleymane; Katsaras, John; Dutcher, John

    Monodisperse phytoglycogen nanoparticles are a promising, new soft colloidal nanomaterial with many applications in the personal care, food, nutraceutical and pharmaceutical industries. These applications rely on exceptional properties that emerge from the highly branched structure of phytoglycogen and its interaction with water, such as extraordinarily high water retention, and low viscosity and exceptional stability in water. The structure and hydration of the nanoparticles was characterized using small angle neutron scattering (SANS) and quasielastic neutron scattering (QENS). SANS allowed us to determine the size of the nanoparticles, evaluate their radial density profile, quantify the particle-to-particle spacing, and determine their water content. The results show clearly that the nanoparticles are highly hydrated, with each nanoparticle containing 250% of its mass in water, and that aqueous dispersions approach a jamming transition at ~ 25% (w/w). QENS experiments provided an independent and consistent measure of the high level of hydration of the particles.

  16. Public Sphere

    DEFF Research Database (Denmark)

    Trenz, Hans-Jörg

    2015-01-01

    of the collective will of the people in the act of democratic self-government. The concept of the public sphere is used across the fields of media and communication research, cultural studies and the humanities, the history of ideas, legal and constitutional studies as well as democracy studies. Historically......In modern societies, the public sphere represents the intermediary realm that supports the communication of opinions, the discovery of problems that need to be dealt with collectively, the channeling of these problems through the filter of the media and political institutions, and the realization......, public spheres have undergone structural transformations that were closely connected to the emergence of different mass media. More recently, they are subject to trends of transnationalization and digitalization in politics and society....

  17. Public Sphere

    DEFF Research Database (Denmark)

    Trenz, Hans-Jörg

    2015-01-01

    In modern societies, the public sphere represents the intermediary realm that supports the communication of opinions, the discovery of problems that need to be dealt with collectively, the channeling of these problems through the filter of the media and political institutions, and the realization......, public spheres have undergone structural transformations that were closely connected to the emergence of different mass media. More recently, they are subject to trends of transnationalization and digitalization in politics and society....... of the collective will of the people in the act of democratic self-government. The concept of the public sphere is used across the fields of media and communication research, cultural studies and the humanities, the history of ideas, legal and constitutional studies as well as democracy studies. Historically...

  18. A Brownian dynamic simulation to verify the effective hard-sphere model criterion for the formation of charged colloidal crystals%带电粒子形成胶体晶体的有效硬球模型判据的计算机模拟验证

    Institute of Scientific and Technical Information of China (English)

    顾凌云; 徐升华; 孙祉伟

    2011-01-01

    在对胶体晶体的研究中,带电粒子胶体晶体的形成机理比硬球胶体晶体更加复杂,对其形成条件目前还缺少有效的判断依据.有效硬球模型判据提出以有效直径作为判断参数.为了验证该判据的有效性,利用布朗动力学模拟研究了不同有效直径下带电粒子胶体晶体的特性.为了更加定量地研究单因素对带电胶体晶体形成的影响,取有效直径为2.8至0.8,并对一定的有效直径,研究了粒子几何直径和排斥力不同情况下的结晶行为.在布朗动力学模拟过程中,采用径向分布函数和键序参数方法检测体系的结构变化,并分析所形成的晶体结构.结果表明,在判断带电粒子胶体体系能否形成有序结构方面,有效硬球模型判据有一定的合理性.但是,并不能将有效直径作为唯一的判别参数,而是需要综合其他参数的影响,这显示出该判据的片面性.%The mechanism for the formation of colloidal crystals in charge-stabilized colloids is more complicated than that of hard-sphere colloidal crystals.And there is still lack of available criterion for the formation of charged colloidal crystals.The effective hard-sphere model suggests a criterion in which the effective diameter is used as a crucial parameter.In order to test the validity of this criterion,the characteristics of charged colloidal crystals with different effective diameters are investigated using Brownian dynamics simulations in this study.The crystallization behaviors with different geometric particle diameters and repulsive forces are also studied with some fixed effective diameters.In the simulation,the time evolution of crystallization process and the crystal structure during the simulation are characterized by means of the radial distribution functions and bond-order parameters.The results show that the effective hard-sphere model criterion has its reasonableness to some extent.However,the effective diameter cannot be

  19. Crystal nucleation of hard spheres using molecular dynamics, umbrella sampling, and forward flux sampling: a comparison of simulation techniques.

    Science.gov (United States)

    Filion, L; Hermes, M; Ni, R; Dijkstra, M

    2010-12-28

    Over the last number of years several simulation methods have been introduced to study rare events such as nucleation. In this paper we examine the crystal nucleation rate of hard spheres using three such numerical techniques: molecular dynamics, forward flux sampling, and a Bennett-Chandler-type theory where the nucleation barrier is determined using umbrella sampling simulations. The resulting nucleation rates are compared with the experimental rates of Harland and van Megen [Phys. Rev. E 55, 3054 (1997)], Sinn et al. [Prog. Colloid Polym. Sci. 118, 266 (2001)], Schätzel and Ackerson [Phys. Rev. E 48, 3766 (1993)], and the predicted rates for monodisperse and 5% polydisperse hard spheres of Auer and Frenkel [Nature 409, 1020 (2001)]. When the rates are examined in units of the long-time diffusion coefficient, we find agreement between all the theoretically predicted nucleation rates, however, the experimental results display a markedly different behavior for low supersaturation. Additionally, we examined the precritical nuclei arising in the molecular dynamics, forward flux sampling, and umbrella sampling simulations. The structure of the nuclei appears independent of the simulation method, and in all cases, the nuclei contains on average significantly more face-centered-cubic ordered particles than hexagonal-close-packed ordered particles.

  20. Effect of excluded volume interactions on the interfacial properties of colloid-polymer mixtures

    NARCIS (Netherlands)

    Fortini, A.; Bolhuis, P.G.; Dijkstra, M.

    2008-01-01

    We report a numerical study of equilibrium phase diagrams and interfacial properties of bulk and confined colloid-polymer mixtures using grand canonical Monte Carlo simulations. Colloidal particles are treated as hard spheres, while the polymer chains are described as soft repulsive spheres. The

  1. Colloidal joints with designed motion range and tunable joint flexibility.

    Science.gov (United States)

    Chakraborty, Indrani; Meester, Vera; van der Wel, Casper; Kraft, Daniela J

    2017-06-14

    The miniaturization of machines towards the micron and nanoscale requires the development of joint-like elements that enable and constrain motion. We present a facile method to create colloidal joints, that is, anisotropic colloidal particles functionalized with surface mobile DNA linkers that control the motion range of bonded particles. We demonstrate quantitatively that we can control the flexibility of these colloidal joints by tuning the DNA linker concentration in the bond area. We show that the shape of the colloidal joint controls the range of motion of bonded particles through a maximisation of the bond area. Using spheres, cubes, and dumbbells, we experimentally realize spherical joints, planar sliders, and hinges, respectively. Finally we demonstrate the potential of the colloidal joints for programmable bottom-up self-assembly by creating flexible colloidal molecules and colloidal polymers. The reconfigurability and motion constraint offered by our colloidal joints make them promising building blocks for the development of switchable materials and nanorobots.

  2. 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.

  3. Site-specific functionalization of anisotropic nanoparticles: from colloidal atoms to colloidal molecules

    DEFF Research Database (Denmark)

    Li, Fan; Yoo, Won Cheol; Beernink, Molly B

    2009-01-01

    Multipodal nanoparticles (NPs) with controlled tethers are promising principal building blocks, useful for constructing more complex materials, much like atoms are connected into more complex molecules. Here we report colloidal sphere templating as a viable means to create tetrapodal NPs with site......-specific tethers. Amorphous sol-gel materials were molded by the template into shaped NPs that mimic tetravalent atoms but on the length scale of colloids. Synthetic methods were developed to modify only the tips of the tetrapods with a range of possible functional groups to generate anisotropic NPs capable...... of directional bonding to other NPs. We also illustrate that sets of tethered "colloidal atoms" can assemble themselves into "colloidal molecules" with precise placement of the modifying colloids. The templating and tethering approaches to these anisotropic colloidal building blocks and the assembly methods...

  4. Colloidal dynamics near a particle-covered surface

    NARCIS (Netherlands)

    Eral, Burak; Mugele, Friedrich Gunther; Duits, Michael H.G.

    2011-01-01

    How the diffusive dynamics of colloidal spheres changes in the vicinity of a particle-coated surface is of importance for industrial challenges such as fouling and sedimentation as well as for fundamental studies into confinement effects. We addressed this question by studying colloidal dynamics in

  5. Phase diagram for a mixture of colloids and polymers with equal size

    NARCIS (Netherlands)

    Tuinier, R.; Smith, P.A.; Poon, W.C.K.; Egelhaaf, S.U.; Aarts, D.G.A.L.; Lekkerkerker, H.N.W.; Fleer, G.J.

    2008-01-01

    We present the phase diagram of a colloid-polymer mixture in which the radius a of the colloidal spheres is approximately the same as the radius R of a polymer coil (q=R/a1). A three-phase coexistence region is experimentally observed, previously only reported for colloid-polymer mixtures with small

  6. Fluid-fluid demixing curves for colloid-polymer mixtures in a random colloidal matrix

    Science.gov (United States)

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2011-12-01

    We study fluid-fluid phase separation in a colloid-polymer mixture adsorbed in a colloidal porous matrix close to the θ point. For this purpose we consider the Asakura-Oosawa model in the presence of a quenched matrix of colloidal hard spheres. We study the dependence of the demixing curve on the parameters that characterize the quenched matrix, fixing the polymer-to-colloid size ratio to 0.8. We find that, to a large extent, demixing curves depend only on a single parameter f, which represents the volume fraction which is unavailable to the colloids. We perform Monte Carlo simulations for volume fractions f equal to 40% and 70%, finding that the binodal curves in the polymer and colloid packing-fraction plane have a small dependence on disorder. The critical point instead changes significantly: for instance, the colloid packing fraction at criticality increases with increasing f. Finally, we observe for some values of the parameters capillary condensation of the colloids: a bulk colloid-poor phase is in chemical equilibrium with a colloid-rich phase in the matrix.

  7. Discrete solvent effects on the effective interaction between charged colloids

    CERN Document Server

    Allahyarov, E

    2000-01-01

    Using computer simulations of two charged colloidal spheres with their counterions in a hard sphere solvent, we show that the granular nature of the solvent significantly influences the effective colloidal interaction. For divalent counterions, the total effective force can become attractive generated by counterion hydration, while for monovalent counterions the forces are repulsive and well-described by a solvent-induced colloidal charge renormalization. Both effects are not contained in the traditional "primitive" approaches but can be accounted for in a solvent-averaged primitive model.

  8. Colloidal Thermal Fluids

    Science.gov (United States)

    Lotzadeh, Saba

    particles where Maxwell's theory is reliable. This method also provides an accurate tool for evaluation of conductivity in colloidal suspensions between Maxwell's limits where theory is inadequate and experiments are limited due to colloidal difficulties. The effect of cluster configuration and degree of aggregation was investigated and showed that clusters of about the same size, but with different structures increases conductivity by different degree. We also showed that even small structural details such as the size of the neck that particles form during aggregation, can change the enhancement significantly. Colloidal clusters conduct heat more efficiently compared to fully dispersed particles at the same volume fraction. We present a predictive model to calculate the thermal conductivity of clusters by extending Maxwell's theory to non-spherical particles. We treat the clusters as spheres with effective thermal conductivity kc and volume fraction φc. We calculate conductivity of the cluster from the upper bound of Maxwell's theory, and the conductivity of a dispersion of such clusters from the lower limit of the theory. We show that structural effects can be represented by a single parameter and a method was provided to obtain this parameter from numerical simulations. We test the theory against simulations as well as dispersions of colloidal cluster and find it to be in very good agreement with both. The results suggest that the variability of literature data and the unusually high values of thermal conductivity that have been reported in the literature can be fully accounted by the presence of clusters. (Abstract shortened by ProQuest.).

  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. Dynamics of Colloids Confined in Microcylinders

    NARCIS (Netherlands)

    Ghosh, Somnath; Wijnperle, Daniël; Mugele, Friedrich Gunther; Duits, Michael H.G.

    2016-01-01

    We studied both global and local effects of cylindrical confinement on the diffusive behavior of hard sphere (HS) colloids. Using confocal scanning laser microscopy (CSLM) and particle tracking, we measured the mean squared displacement (MSD) of 1 micron sized silica particles in water–glycerol.

  11. Cubic colloids : Synthesis, functionalization and applications

    NARCIS (Netherlands)

    Castillo, S.I.R.

    2015-01-01

    This thesis is a study on cubic colloids: micron-sized cubic particles with rounded corners (cubic superballs). Owing to their shape, particle packing for cubes is more efficient than for spheres and results in fascinating phase and packing behavior. For our cubes, the particle volume fraction when

  12. Cubic colloids : Synthesis, functionalization and applications

    NARCIS (Netherlands)

    Castillo, S.I.R.

    2015-01-01

    This thesis is a study on cubic colloids: micron-sized cubic particles with rounded corners (cubic superballs). Owing to their shape, particle packing for cubes is more efficient than for spheres and results in fascinating phase and packing behavior. For our cubes, the particle volume fraction when

  13. Memory effects in metal-oxide-semiconductor capacitors incorporating dispensed highly monodisperse 1 nm silicon nanoparticles

    Science.gov (United States)

    Nayfeh, Osama M.; Antoniadis, Dimitri A.; Mantey, Kevin; Nayfeh, Munir H.

    2007-04-01

    Metal-oxide-semiconductor capacitors containing various densities of ex situ produced, colloidal, highly monodisperse, spherical, 1nm silicon nanoparticles were fabricated and evaluated for potential use as charge storage elements in future nonvolatile memory devices. The capacitance-voltage characteristics are well behaved and agree with similarly fabricated zero-nanoparticle control samples and with an ideal simulation. Unlike larger particle systems, the demonstrated memory effect exhibits effectively pure hole storage. The nature of charging, hole type versus electron type may be understood in terms of the characteristics of ultrasmall silicon nanoparticles: large energy gap, large charging energy, and consequently a small electron affinity.

  14. Quasisymmetric Spheres

    Directory of Open Access Journals (Sweden)

    Vellis Vyron

    2016-03-01

    Full Text Available Let Ω be a planar Jordan domain and α > 0. We consider double-dome-like surfaces Σ(Ω, tα over Ω where the height of the surface over any point x ∈ Ωequals dist(x, ∂Ωα. We identify the necessary and sufficient conditions in terms of and α so that these surfaces are quasisymmetric to S2 and we show that Σ(Ω, tα is quasisymmetric to the unit sphere S2 if and only if it is linearly locally connected and Ahlfors 2-regular.

  15. A granocentric model captures the statistical properties of monodisperse random packings

    CERN Document Server

    Newhall, Katherine A; Vanden-Eijnden, Eric; Brujic, Jasna

    2012-01-01

    We present a generalization of the granocentric model proposed in [Clusel et al., Nature, 2009, 460, 611615] that is capable of describing the local fluctuations inside not only polydisperse but also monodisperse packings of spheres. This minimal model does not take into account the relative particle positions, yet it captures positional disorder through local stochastic processes sampled by efficient Monte Carlo methods. The disorder is characterized by the distributions of local parameters, such as the number of neighbors and contacts, filled solid angle around a central particle and the cell volumes. The model predictions are in good agreement with our experimental data on monodisperse random close packings of PMMA particles. Moreover, the model can be used to predict the distributions of local fluctuations in any packing, as long as the average number of neighbors, contacts and the packing fraction are known. These distributions give a microscopic foundation to the statistical mechanics framework for jamm...

  16. 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

  17. Partial structure factors in star polymer/colloid mixtures

    CERN Document Server

    Stellbrink, J; Richter, D; Moussaid, A; Schofield, A B; Poon, W C K; Pusey, P N; Lindner, P; Dzubiella, J; Likos, C N; Löwen, H

    2002-01-01

    Addition of polymer to colloidal suspensions induces an attractive part to the colloid pair potential, which is of purely entropic origin (''depletion interaction''). We investigated the influence of polymer branching on depletion forces by studying mixtures of hard sphere colloids and star polymers with increasing arm number f=2-32, but constant R sub g approx 500 A. We found a pronounced effect of branching on the position of the gas/liquid demixing transition. Using small angle neutron scattering (SANS) we were able to measure partial structure factors in star polymer/colloid mixtures. The relative distance to the demixing transition is reflected in our scattering data. (orig.)

  18. Spontaneous Breakup of Extended Monodisperse Polymer Melts

    DEFF Research Database (Denmark)

    Rasmussen, Henrik K.; Yu, Kaijia

    2011-01-01

    We apply continuum mechanical based, numerical modeling to study the dynamics of extended monodisperse polymer melts during the relaxation. The computations are within the ideas of the microstructural ‘‘interchain pressure’’ theory. The computations show a delayed necking resulting in a rupture...

  19. Linear Optical Properties of Gold Colloid

    Directory of Open Access Journals (Sweden)

    Jingmin XIA

    2015-11-01

    Full Text Available Gold colloid was prepared by reducing HAuCl4·4H2O with Na3C6H5O7·2H2O. The morphology, size of gold nanoparticles and the optical property of colloid were characterized by transmission electron microscope and UV-Vis spectrophotometer, respectively. It shows that the gold nanoparticles are in the shape of spheres with diameters less than 8 nm, and the surface plasmon resonance absorption peak is located at about 438 nm. As the volume fraction of gold particles increases, the intensity of absorption peak strengthens. The optical property of gold colloid was analyzed by Maxwell-Garnett (MG effective medium theory in the company of Drude dispersion model. The results show that the matrix dielectric constant is a main factor, which influences the optical property of gold colloid.DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9558

  20. Separation of colloidal two dimensional materials by density gradient ultracentrifugation

    Energy Technology Data Exchange (ETDEWEB)

    Kuang, Yun; Song, Sha [State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029 (China); Huang, Jinyang, E-mail: huangjy@mail.buct.edu.cn [Department of Mathematics, College of Science, Beijing University of Chemical Technology, Beijing 100029 (China); Sun, Xiaoming, E-mail: sunxm@mail.buct.edu.cn [State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029 (China)

    2015-04-15

    Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials. Isopycnic separation was applied on thickness-dependent separation of graphene nanosheets. And rate-zonal separation, as a more versatile separation method, demonstrated its capability in sorting nanosheets of chemically modified single layered graphene, layered double hydroxide, and even metallic Ag. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Graphical abstract: Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials according to their size of thickness difference. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Highlights: • Density gradient ultracentrifugation was applied on size separation of 2D material. • Isopycnic separation was applied on separation of low density materials. • Rate-zonal separation was applied on separation of large density materials. • Size

  1. Free volume distribution of nearly jammed hard sphere packings

    Science.gov (United States)

    Maiti, Moumita; Sastry, Srikanth

    2014-07-01

    We calculate the free volume distributions of nearly jammed packings of monodisperse and bidisperse hard sphere configurations. These distributions differ qualitatively from those of the fluid, displaying a power law tail at large free volumes, which constitutes a distinct signature of nearly jammed configurations, persisting for moderate degrees of decompression. We reproduce and explain the observed distribution by considering the pair correlation function within the first coordination shell for jammed hard sphere configurations. We analyze features of the equation of state near jamming, and discuss the significance of observed asphericities of the free volumes to the equation of state.

  2. 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

  3. 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.

  4. Seed mediated synthesis of highly mono-dispersed gold nanoparticles in the presence of hydroquinone

    Science.gov (United States)

    Kumar, Dhiraj; Mutreja, Isha; Sykes, Peter

    2016-09-01

    Gold nanoparticles (AuNPs) are being studied for several biomedical applications, including drug delivery, biomedical imaging, contrast agents and tumor targeting. The synthesis of nanoparticles with a narrow size distribution is critical for these applications. We report the synthesis of highly mono-dispersed AuNPs by a seed mediated approach, in the presence of tri-sodium citrate and hydroquinone (HQ). AuNPs with an average size of 18 nm were used for the synthesis of highly mono-dispersed nanocrystals of an average size 40 nm, 60 nm, 80 nm and ˜100 nm; but the protocol is not limited to these sizes. The colloidal gold was subjected to UV-vis absorbance spectroscopy, showing a red shift in lambda max wavelength, peaks at 518.47 nm, 526.37 nm, 535.73 nm, 546.03 nm and 556.50 nm for AuNPs seed (18 nm), 40 nm, 60 nm, 80 nm and ˜100 nm respectively. The analysis was consistent with dynamic light scattering and electron microscopy. Hydrodynamic diameters measured were 17.6 nm, 40.8 nm, 59.8 nm, 74.1 nm, and 91.4 nm (size by dynamic light scattering—volume %); with an average poly dispersity index value of 0.088, suggesting mono-dispersity in the size distribution, which was also confirmed by transmission electron microscopy analysis. The advantage of a seed mediated approach is a multi-step growth of nanoparticle size that enables us to control the number of nanoparticles in the suspension, for size ranging from 24.5 nm to 95.8 nm. In addition, the HQ-based synthesis of colloidal nanocrystals allowed control of the particle size and size distribution by tailoring either the number of seeds, amount of gold precursor or reducing agent (HQ) in the final reaction mixture.

  5. Seed mediated synthesis of highly mono-dispersed gold nanoparticles in the presence of hydroquinone.

    Science.gov (United States)

    Kumar, Dhiraj; Mutreja, Isha; Sykes, Peter

    2016-09-02

    Gold nanoparticles (AuNPs) are being studied for several biomedical applications, including drug delivery, biomedical imaging, contrast agents and tumor targeting. The synthesis of nanoparticles with a narrow size distribution is critical for these applications. We report the synthesis of highly mono-dispersed AuNPs by a seed mediated approach, in the presence of tri-sodium citrate and hydroquinone (HQ). AuNPs with an average size of 18 nm were used for the synthesis of highly mono-dispersed nanocrystals of an average size 40 nm, 60 nm, 80 nm and ∼100 nm; but the protocol is not limited to these sizes. The colloidal gold was subjected to UV-vis absorbance spectroscopy, showing a red shift in lambda max wavelength, peaks at 518.47 nm, 526.37 nm, 535.73 nm, 546.03 nm and 556.50 nm for AuNPs seed (18 nm), 40 nm, 60 nm, 80 nm and ∼100 nm respectively. The analysis was consistent with dynamic light scattering and electron microscopy. Hydrodynamic diameters measured were 17.6 nm, 40.8 nm, 59.8 nm, 74.1 nm, and 91.4 nm (size by dynamic light scattering-volume %); with an average poly dispersity index value of 0.088, suggesting mono-dispersity in the size distribution, which was also confirmed by transmission electron microscopy analysis. The advantage of a seed mediated approach is a multi-step growth of nanoparticle size that enables us to control the number of nanoparticles in the suspension, for size ranging from 24.5 nm to 95.8 nm. In addition, the HQ-based synthesis of colloidal nanocrystals allowed control of the particle size and size distribution by tailoring either the number of seeds, amount of gold precursor or reducing agent (HQ) in the final reaction mixture.

  6. 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,...

  7. Hard sphere packings within cylinders.

    Science.gov (United States)

    Fu, Lin; Steinhardt, William; Zhao, Hao; Socolar, Joshua E S; Charbonneau, Patrick

    2016-03-07

    Arrangements of identical hard spheres confined to a cylinder with hard walls have been used to model experimental systems, such as fullerenes in nanotubes and colloidal wire assembly. Finding the densest configurations, called close packings, of hard spheres of diameter σ in a cylinder of diameter D is a purely geometric problem that grows increasingly complex as D/σ increases, and little is thus known about the regime for D > 2.873σ. In this work, we extend the identification of close packings up to D = 4.00σ by adapting Torquato-Jiao's adaptive-shrinking-cell formulation and sequential-linear-programming (SLP) technique. We identify 17 new structures, almost all of them chiral. Beyond D ≈ 2.85σ, most of the structures consist of an outer shell and an inner core that compete for being close packed. In some cases, the shell adopts its own maximum density configuration, and the stacking of core spheres within it is quasiperiodic. In other cases, an interplay between the two components is observed, which may result in simple periodic structures. In yet other cases, the very distinction between the core and shell vanishes, resulting in more exotic packing geometries, including some that are three-dimensional extensions of structures obtained from packing hard disks in a circle.

  8. Colloids and polymers in random colloidal matrices: Demixing under good-solvent conditions

    Science.gov (United States)

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2012-10-01

    We consider a simplified coarse-grained model for colloid-polymer mixtures, in which polymers are represented as monoatomic molecules interacting by means of pair potentials. We use it to study polymer-colloid segregation in the presence of a quenched matrix of colloidal hard spheres. We fix the polymer-to-colloid size ratio to 0.8 and consider matrices such that the fraction f of the volume that is not accessible to the colloids due to the matrix is equal to 40%. As in the Asakura-Oosawa-Vrij (AOV) case, we find that binodal curves in the polymer and colloid volume-fraction plane have a small dependence on disorder. As for the position of the critical point, the behavior differs from that observed in the AOV case: While the critical colloid volume fraction is essentially the same in the bulk and in the presence of the matrix, the polymer volume fraction at criticality increases as f increases. At variance with the AOV case, no capillary colloid condensation or evaporation is generically observed.

  9. Synthesis and Applications of Non-spherical Dimer Colloids

    Science.gov (United States)

    Yoon, Kisun

    Colloids are promising building blocks in material synthesis because of their controllability of size and surface properties. The synthesis of chemically and/or geometrically anisotropic colloidal particles has received attentions with the expectation of building blocks for complex structures. However, the synthesis of anisotropic colloidal particles is by far more difficult than the synthesis of spherical colloidal particles. Lack of monodispersity and productivity of many anisotropic particles often limits their applications as a building block for complex structures. Thus, it is highly desirable to develop methods which can produce a large amount of monodisperse non-spherical particles with controllable asymmetric surface properties. This dissertation details the work for developing such a method. The major result of this dissertation is a synthetic method to produce monodisperse non-spherical colloids with anisotropic surface property in a large quantity. The anisotropic colloid, which we call it as Dimer particle, has two fused lobes like a dumbbell and each lobe's size can be independently controlled. We present a novel method to synthesize sub-micron size Dimer particles. This method can produce a large amount of submicron-sized Dimer particles with good monodispersity and well-controlled shape. Submicron-sized Dimer particles have been highly desired since they can be used as a building block for self assembly using Brownian motion, colloidal surfactant for Pickering emulsion, and photonic materials. To fully take advantage of the anisotropy of the particles, we develop a facile method to tailor the surface property of each lobe independently by asymmetrically coating the particles with gold nanoparticles. This method doesn't need the arrangement of particles onto any type of interfaces. Asymmetric coating of gold nanoparticles can be carried out simply by mixing Dimer particles with gold nanoparticles. The formation mechanism of the submicron-sized Dimer

  10. Close packing density of polydisperse hard spheres.

    Science.gov (United States)

    Farr, Robert S; Groot, Robert D

    2009-12-28

    The most efficient way to pack equally sized spheres isotropically in three dimensions is known as the random close packed state, which provides a starting point for many approximations in physics and engineering. However, the particle size distribution of a real granular material is never monodisperse. Here we present a simple but accurate approximation for the random close packing density of hard spheres of any size distribution based upon a mapping onto a one-dimensional problem. To test this theory we performed extensive simulations for mixtures of elastic spheres with hydrodynamic friction. The simulations show a general (but weak) dependence of the final (essentially hard sphere) packing density on fluid viscosity and on particle size but this can be eliminated by choosing a specific relation between mass and particle size, making the random close packed volume fraction well defined. Our theory agrees well with the simulations for bidisperse, tridisperse, and log-normal distributions and correctly reproduces the exact limits for large size ratios.

  11. Template synthesis of monodisperse carbon nanodots

    Science.gov (United States)

    Kurdyukov, D. A.; Eurov, D. A.; Stovpiaga, E. Yu.; Kirilenko, D. A.; Konyakhin, S. V.; Shvidchenko, A. V.; Golubev, V. G.

    2016-12-01

    Monodisperse carbon nanodots in pores of mesoporous silica particles are obtained by template synthesis. This method is based on introducing a precursor (organosilane) into pores, its thermal decomposition with formation of carbon nanodots, and the template removal. Structural analysis of the nanomaterial has been performed, which showed that carbon nanodots have an approximately spherical form and a graphite-like structure. According to dynamic light scattering data, the size of carbon nanodots is 3.3 ± 0.9 nm.

  12. Multifunctional assembly of micrometer-sized colloids for cell sorting.

    Science.gov (United States)

    Nie, Chenyao; Wang, Bing; Zhang, Jiangyan; Cheng, Yongqiang; Lv, Fengting; Liu, Libing; Wang, Shu

    2015-06-03

    Compared to the extensively studied nanometer-sized colloids, less attention has been paid to the assembly of micrometer-sized colloids with multifunctional characteristics. To address this need, a bottom-up approach is developed for constructing self-assemblies of micrometer-sized magnetic colloids possessing multifunctionality, including magnetic, optical, and biological activities. Biotinylated oligo (p-phenylene vinylene) (OPV) derivatives are designed to mediate the self-assembly of streptavidin-modified magnetic beads. The optical element OPV derivatives provide a fluorescence imaging ability for tracing the assembly process. Target cells can be recognized and assembled by the colloidal assembly with bioactive element antibodies. The colloidal assembly reveals better cell isolation performance by its amplified magnetic response in comparison to monodisperse colloids. The self-assembly of micrometer-sized magnetic colloids through a combination of different functional ingredients to realize multifunction is conceptually simple and easy to achieve. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. The interplay of sedimentation and crystallization in hard-sphere suspensions

    NARCIS (Netherlands)

    Russo, J.; Maggs, A.C.; Bonn, D.; Tanaka, H.

    2013-01-01

    We study crystal nucleation under the influence of sedimentation in a model of colloidal hard spheres via Brownian dynamics simulations. We introduce two external fields acting on the colloidal fluid: a uniform gravitational field (body force), and a surface field imposed by pinning a layer of equil

  14. Monte Carlo simulations of in-plane stacking disorder in hard-sphere crystals

    NARCIS (Netherlands)

    Miedema, P.S.; de Villeneuve, V.W.A.; Petukhov, A.V.

    2008-01-01

    On-lattice Monte Carlo simulations of colloidal random-stacking hard-sphere colloidal crystals are presented. The model yields close-packed crystals with random-stacking hexagonal structure. We find a significant amount of in-plane stacking disorder, which slowly anneals in the course of the simulat

  15. Imitation of variable structural color in Paracheirodon innesi using colloidal crystal films.

    Science.gov (United States)

    Cong, Hailin; Yu, Bing; Zhao, Xiu Song

    2011-06-20

    Spacing variation of adjoining reflecting thin films in iridophore is responsible for the variable interference color in the paracheirodon innesi. On the basis of this phenomenon, colloidal crystal thin films with different structures are fabricated from monodisperse poly(styrene-methyl methacrylate-acrylic acid) (PSMA) colloids. The relationship between the colors and structures of the films is investigated and discussed according to the principle of light interference. A two-layer colloidal film having uniform color is researched and it displays diverse colors before and after swelling by styrene (St), which can be used to mimic the variable structural color of the paracheirodon innesi.

  16. PROGRESS IN THREE-DIMENSIONALLY ORDERED SELF-ASSEMBLY OF COLLOIDAL SiO2 PARTICLES

    Institute of Scientific and Technical Information of China (English)

    Qian Zhou; Peng Dong; Bingying Cheng

    2003-01-01

    Three-dimensionally ordered self-assembly of monodispersed colloidal SiO2 particles involving a structure with periodic alternation of refractive indices represents an advanced field of particuology, colloidal chemistry, materials science, optical physics and information science. Study on such self-assembly not only lays the foundation for the development of advanced functional materials, but also is significant in understanding the principles of nano- and micro-scale processes. Recent progress in three-dimensionally ordered self-assembly of colloidal SiO2 particles is reviewed,inclusive of the authors' investigations.

  17. Phase diagrams of binary mixtures of oppositely charged colloids.

    Science.gov (United States)

    Bier, Markus; van Roij, René; Dijkstra, Marjolein

    2010-09-28

    Phase diagrams of binary mixtures of oppositely charged colloids are calculated theoretically. The proposed mean-field-like formalism interpolates between the limits of a hard-sphere system at high temperatures and the colloidal crystals which minimize Madelung-like energy sums at low temperatures. Comparison with computer simulations of an equimolar mixture of oppositely charged, equally sized spheres indicate semiquantitative accuracy of the proposed formalism. We calculate global phase diagrams of binary mixtures of equally sized spheres with opposite charges and equal charge magnitude in terms of temperature, pressure, and composition. The influence of the screening of the Coulomb interaction upon the topology of the phase diagram is discussed. Insight into the topology of the global phase diagram as a function of the system parameters leads to predictions on the preparation conditions for specific binary colloidal crystals.

  18. Mesoscopic model of temporal and spatial heterogeneity in aging colloids

    DEFF Research Database (Denmark)

    Becker, Nikolaj; Sibani, Paolo; Boettcher, Stefan

    2014-01-01

    We develop a simple and effective description of the dynamics of dense hard sphere colloids in the aging regime deep in the glassy phase. Our description complements the many efforts to understand the onset of jamming in low density colloids, whose dynamics is still time-homogeneous. Based...... on a small set of principles, our model provides emergent dynamic heterogeneity, reproduces the known results for dense hard sphere colloids and makes detailed, experimentally-testable predictions for canonical observables in glassy dynamics. In particular, we reproduce the shape of the intermediate...... scattering function and particle mean-square displacements for jammed colloidal systems, and we predict a growth for the peak of the χ4 mobility correlation function that is logarithmic in waiting-time. At the same time, our model suggests a novel unified description for the irreversible aging dynamics...

  19. 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

  20. Binary Colloidal Alloy Test-3 and 4: Critical Point

    Science.gov (United States)

    Weitz, David A.; Lu, Peter J.

    2007-01-01

    Binary Colloidal Alloy Test - 3 and 4: Critical Point (BCAT-3-4-CP) will determine phase separation rates and add needed points to the phase diagram of a model critical fluid system. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

  1. Self-replication with magnetic dipolar colloids.

    Science.gov (United States)

    Dempster, Joshua M; Zhang, Rui; Olvera de la Cruz, Monica

    2015-10-01

    Colloidal self-replication represents an exciting research frontier in soft matter physics. Currently, all reported self-replication schemes involve coating colloidal particles with stimuli-responsive molecules to allow switchable interactions. In this paper, we introduce a scheme using ferromagnetic dipolar colloids and preprogrammed external magnetic fields to create an autonomous self-replication system. Interparticle dipole-dipole forces and periodically varying weak-strong magnetic fields cooperate to drive colloid monomers from the solute onto templates, bind them into replicas, and dissolve template complexes. We present three general design principles for autonomous linear replicators, derived from a focused study of a minimalist sphere-dimer magnetic system in which single binding sites allow formation of dimeric templates. We show via statistical models and computer simulations that our system exhibits nonlinear growth of templates and produces nearly exponential growth (low error rate) upon adding an optimized competing electrostatic potential. We devise experimental strategies for constructing the required magnetic colloids based on documented laboratory techniques. We also present qualitative ideas about building more complex self-replicating structures utilizing magnetic colloids.

  2. Directed self-assembly of a colloidal kagome lattice.

    Science.gov (United States)

    Chen, Qian; Bae, Sung Chul; Granick, Steve

    2011-01-20

    A challenging goal in materials chemistry and physics is spontaneously to form intended superstructures from designed building blocks. In fields such as crystal engineering and the design of porous materials, this typically involves building blocks of organic molecules, sometimes operating together with metallic ions or clusters. The translation of such ideas to nanoparticles and colloidal-sized building blocks would potentially open doors to new materials and new properties, but the pathways to achieve this goal are still undetermined. Here we show how colloidal spheres can be induced to self-assemble into a complex predetermined colloidal crystal-in this case a colloidal kagome lattice-through decoration of their surfaces with a simple pattern of hydrophobic domains. The building blocks are simple micrometre-sized spheres with interactions (electrostatic repulsion in the middle, hydrophobic attraction at the poles, which we call 'triblock Janus') that are also simple, but the self-assembly of the spheres into an open kagome structure contrasts with previously known close-packed periodic arrangements of spheres. This open network is of interest for several theoretical reasons. With a view to possible enhanced functionality, the resulting lattice structure possesses two families of pores, one that is hydrophobic on the rims of the pores and another that is hydrophilic. This strategy of 'convergent' self-assembly from easily fabricated colloidal building blocks encodes the target supracolloidal architecture, not in localized attractive spots but instead in large redundantly attractive regions, and can be extended to form other supracolloidal networks.

  3. Crystallizing hard-sphere glasses by doping with active particles

    NARCIS (Netherlands)

    Ni, Ran; Cohen Stuart, M.A.; Dijkstra, M.; Bolhuis, P.G.

    2014-01-01

    Crystallization and vitrification are two different routes to form a solid. Normally these two processes suppress each other, with the glass transition preventing crystallization at high density (or low temperature). This is even true for systems of colloidal hard spheres, which are commonly used as

  4. 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

  5. Direct Observation of the Formation of Liquid Protrusions on Polymer Colloids and their Coalescence

    NARCIS (Netherlands)

    Peng, B.; van Blaaderen, A.; Imhof, A.

    2013-01-01

    Monodisperse nonspherical poly (methyl methacrylate) (PMMA) particles where a central core particle had grown two extra “lobes”, or protrusions, placed opposite each other were successfully synthesized by swelling and subsequent polymerization of cross-linked PMMA spheres with methyl methacrylate an

  6. Rheology and dynamics of colloidal superballs.

    Science.gov (United States)

    Royer, John R; Burton, George L; Blair, Daniel L; Hudson, Steven D

    2015-07-28

    Recent advances in colloidal synthesis make it possible to generate a wide array of precisely controlled, non-spherical particles. This provides a unique opportunity to probe the role that particle shape plays in the dynamics of colloidal suspensions, particularly at higher volume fractions, where particle interactions are important. We examine the role of particle shape by characterizing both the bulk rheology and micro-scale diffusion in a suspension of pseudo-cubic silica superballs. Working with these well-characterized shaped colloids, we can disentangle shape effects in the hydrodynamics of isolated particles from shape-mediated particle interactions. We find that the hydrodynamic properties of isolated superballs are marginally different from comparably sized hard spheres. However, shape-mediated interactions modify the suspension microstructure, leading to significant differences in the self-diffusion of the superballs. While this excluded volume interaction can be captured with a rescaling of the superball volume fraction, we observe qualitative differences in the shear thickening behavior of moderately concentrated superball suspensions that defy simple rescaling onto hard sphere results. This study helps to define the unknowns associated with the effects of shape on the rheology and dynamics of colloidal solutions.

  7. Clustering and gelation of hard spheres induced by the Pickering effect

    Science.gov (United States)

    Fortini, Andrea

    2012-04-01

    A mixture of hard-sphere particles and model emulsion droplets is studied with a Brownian dynamics simulation. We find that the addition of nonwetting emulsion droplets to a suspension of pure hard spheres can lead to both gas-liquid and fluid-solid phase separations. Furthermore, we find a stable fluid of hard-sphere clusters. The stability is due to the saturation of the attraction that occurs when the surface of the droplets is completely covered with colloidal particles. At larger emulsion droplet densities a percolation transition is observed. The resulting networks of colloidal particles show dynamical and mechanical properties typical of a colloidal gel. The results of the model are in good qualitative agreement with recent experimental findings [E. Koos and N. Willenbacher, ScienceSCIEAS0036-807510.1126/science.1199243 331, 897 (2011)] in a mixture of colloidal particles and two immiscible fluids.

  8. Probing the evolution and morphology of hard carbon spheres

    Energy Technology Data Exchange (ETDEWEB)

    Pol, Vilas G.; Wen, Jianguo; Lau, Kah Chun; Callear, Samantha; Bowron, Daniel T.; Lin, Chi-Kai; Deshmukh, Sanket A.; Sankaranarayanan, Subramanian; Curtiss, Larry A.; David, William; Miller, Dean J.; Thackeray, Michael M.

    2014-03-01

    Monodispersed hard carbon spheres can be synthesized quickly and reproducibly by autogenic reactions of hydrocarbon precursors, notably polyethylene (including plastic waste), at high temperature and pressure. The carbon microparticles formed by this reaction have a unique spherical architecture, with a dominant internal nanometer layered motif, and they exhibit diamond-like hardness and electrochemical properties similar to graphite. In the present study, in-situ monitoring by X-ray diffraction along with electron microscopy, Raman spectroscopy, neutron pair-distribution function analysis, and computational modeling has been used to elucidate the morphology and evolution of the carbon spheres that form from the autogenic reaction of polyethylene at high temperature and pressure. A mechanism is proposed on how polyethylene evolves from a linear chain-based material to a layered carbon motif. Heating the spheres to 2400-2800 °C under inert conditions increases their graphitic character, particularly at the surface, which enhances their electrochemical and tribological properties.

  9. Brownian versus Newtonian devitrification of hard-sphere glasses

    Science.gov (United States)

    Montero de Hijes, Pablo; Rosales-Pelaez, Pablo; Valeriani, Chantal; Pusey, Peter N.; Sanz, Eduardo

    2017-08-01

    In a recent molecular dynamics simulation work it has been shown that glasses composed of hard spheres crystallize via cooperative, stochastic particle displacements called avalanches [E. Sanz et al., Proc. Natl. Acad. Sci. USA 111, 75 (2014), 10.1073/pnas.1308338110]. In this Rapid Communication we investigate if such a devitrification mechanism is also present when the dynamics is Brownian rather than Newtonian. The research is motivated in part by the fact that colloidal suspensions, an experimental realization of hard-sphere systems, undergo Brownian motion. We find that Brownian hard-sphere glasses do crystallize via avalanches with very similar characteristics to those found in the Newtonian case. We briefly discuss the implications of these findings for experiments on colloids.

  10. Fabrication of anisotropic multifunctional colloidal carriers

    Science.gov (United States)

    Jerri, Huda A.

    The field of colloidal assembly has grown tremendously in recent years, although the direct or template-assisted methods used to fabricate complex colloidal constructions from monodisperse micro- and nanoparticles have been generally demonstrated on model materials. In this work, novel core particle syntheses, particle functionalizations and bottom-up assembly techniques are presented to create functional colloidal devices. Using particle lithography, high-information colloidal vectors have been developed and modified with imaging and targeting agents. Localized nanoscale patches have been reliably positioned on microparticles to serve as foundations for further chemical or physical modifications. Site-specific placement of RGD targeting ligands has been achieved in these lithographed patches. Preferential uptake of these targeted vectors by RGD-specific 3T3 fibroblasts was verified using confocal laser scanning microscopy. A transition was made from the functionalization of model imaging core particles to the lithography of colloidal cartridges, in an effort to construct colloidal syringes with specialized, programmable release profiles. A variety of functional, pH-sensitive fluorescent cores were engineered to respond to solution conditions. When triggered, the diverse composite core microparticles and reservoir microcapsules released embedded fluorescent moieties such as dye molecules, and fluorophore-conjugated nanoparticles. The microcapsules, created using layer-by-layer polyelectrolyte deposition on sacrificial templates, were selectively modified with a robust coating. The pH-responsive anisotropic reservoir microcapsules were extremely stable in solution, and exhibited a "Lazarus" functionality of rehydrating to their original state following desiccation. A snapshot of focused-release of core constituents through the lone opening in colloidal monotremes has been obtained by anisotropically-functionalizing degradable cores with barrier shells. Additionally

  11. Multidensity integral-equation theory for short diblock hard-sphere-sticky-hard-sphere chains.

    Science.gov (United States)

    Wu, Ning; Chiew, Y C

    2010-04-01

    The multidensity Ornstein-Zernike integral equation theory is applied to study a simple model of hard sphere/sticky hard sphere diblock chains. The multidensity integral equation formalism has been successfully used to model the equilibrium structure and thermodynamic properties of homonuclear chains and shorter dimer fluids; to our knowledge it has not been applied to model diblock chains. In this work, a diblock chain fluids is represented by an m-component equal molar mixture of hard spheres with species 1,2,...,mh and sticky hard spheres with species mh+1,mh+2,...,m. Each spherical particle has two attractive sites A and B except species 1 and m, which have only one site per particle. In the limit of complete association, this mixture yields a system of monodisperse diblock chains. A general solution of this model is obtained in the Percus-Yevick, Polymer Percus-Yevick and ideal chain approximations. Both structural and thermodynamic properties of this model are investigated. From this study, a microphase separation is predicted for relatively short diblock symmetric and asymmetric chains. This microphase separation is enhanced at lower temperature and higher density. When chain length increases, the phase transition changes from a microphase level to a macrophase level. The size of microdomain structure is found to be dependent on total chain length, relative ratio of block lengths, temperature, and density.

  12. Microfluidic Production of Monodisperse Perfluorocarbon Microdroplets

    Science.gov (United States)

    Li, David; Schalte, Kevin; Fowlkes, J. Brian; Bull, Joseph

    2010-11-01

    Acoustic droplet vaporization (ADV) is process in which liquid perfluorocarbon (PFC) microdroplets are vaporized using focused ultrasound to form gas bubbles that are approximately 125 times larger in volume. Gas embolotherapy is a novel cancer treatment that uses ADV in vivo to strategically form gas emoboli, which can lodge in the microcirculation and starve tumors. Current methods to produce PFC microdroplets, such has high speed shaking or sonication, result in polydisperse droplet distributions where a fraction of droplets fall within the 2-10 microns range. In the clinical application with such a droplet distribution, large droplets are filtered by the lungs and small droplets result in bubbles that are too small to lodge in the tumor vasculature. Consequently, there is a need for a monodisperse droplet distribution. A microfluidic based device has been developed in order to produce such monodisperse PFC microdroplets. The device used hydrodynamic flow focusing to create droplets with a mean diameter less than 10 microns in diameter. This work is supported by NIH grant R01EB006476.

  13. Recent advances in polymer colloidal crystal lasers.

    Science.gov (United States)

    Furumi, Seiichi

    2012-09-21

    Colloids with a size in the nanometres to micrometres range are frequently used in both fundamental research and industrial applications. In this context, colloidal crystals (CCs)-3D ordered arrays of monodispersed colloidal microparticles with a diameter of several hundred nanometres-have garnered a great deal of attention in the intriguing research realm of photonic crystals (PCs) due to the feasible and high-throughput 3D-PC fabrication with CCs. For optoelectronic applications, it is of prime importance to construct 3D-PCs with photonic band-gaps (PBGs) in the visible wavelength range. With regard to photonic device applications, many reports have been made on a wide variety of optical reflection sensors and displays using CCs that shift the visible PBG wavelength in response to external stimuli. This Minireview describes the research progress in the investigation of CCs and their laser applications. We highlight not only the research background of CCs as 3D-PCs, but also new potential applications of CCs as flexible and widely tunable lasers by low-threshold optical excitation.

  14. Dissipative Particle Dynamics simulation of colloidal suspensions

    Science.gov (United States)

    Jamali, Safa; Boromand, Arman; Maia, Joao

    2014-03-01

    DPD as a mesoscale method was firstly proposed to study dynamics of suspensions under flow condition. However the proposed method failed to capture shear properties of suspensions because it lacked: first a potential to reproduce lubrication forces and second a clear definition for the colloid surface. Recently we reported a modified DPD method which defines colloidal particles as particles with hard core and a dissipative coat. An additional lubrication force was introduced to include the short-range hydrodynamics that are not captured in original DPD. The model was found to be able to reproduce shear properties of suspensions for a wide range of different systems, from monodisperse to bimodal with different volume fractions, compositions and size ratios. In present work our modified DPD method is employed to study both equilibrium and flow properties of colloidal suspension. Zero shear viscosity of suspension is measured using Green-Kubo expressions and the results are compared to theoretical predictions. Furthermore, structure formation in suspensions is studied in respect to energy landscape of the fluid both at rest and under flow.

  15. Elongational viscosity of monodisperse and bidisperse polystyrene melts

    DEFF Research Database (Denmark)

    Nielsen, Jens Kromann; Rasmussen, Henrik K.; Hassager, Ole

    2006-01-01

    The start-up and steady uniaxial elongational viscosity have been measured for two monodisperse polystyrene melts with molecular weights of 52 and 103 kg/mole, and for three bidisperse polystyrene melts. The monodisperse melts show a maximum in the steady elongational viscosity vs. the elongation...

  16. Synthesis and characterization of monodispersed inorganic/organic core/shell microspheres with fluorescence

    Institute of Scientific and Technical Information of China (English)

    ZHANG Kai; HAN Kun; ZHANG Xuehai; YANG Bai

    2005-01-01

    @@ In recent years, the semiconductor nanocrystals (NCs) have attracted great interest due to their potentials in photonics, electronics, magnetics and catalysis, and the monodispersed organic or inorganic microspheres doped NCs display predominant characteristics in the fabrication and study for photonic crystals[1,2], and considerable effort has been devoted to the design and synthesis of CdTe NCs doped colloid with well fluorescence[3-8]. For example, CdTe NCs were fabricated on the surfaces of silica or polymer microspheres by the methods of layer-by-layer assembly, and CdTe NCs were also doped into inorganic or organic microspheres through sol-gel process or swell- ing.

  17. Efficient thermolysis route to monodisperse Cu₂ZnSnS₄ nanocrystals with controlled shape and structure.

    Science.gov (United States)

    Zhang, Xiaoyan; Guo, Guobiao; Ji, Cheng; Huang, Kai; Zha, Chenyang; Wang, Yifeng; Shen, Liming; Gupta, Arunava; Bao, Ningzhong

    2014-05-28

    Monodisperse Cu2ZnSnS4 (CZTS) nanocrystals with tunable shape, crystalline phase, and composition are synthesized by efficient thermolysis of a single source precursor of mixed metal-oleate complexes in hot organic solvents with dissolved sulfur sources. Suitable tuning of the synthetic conditions and the Cu/(Zn + Sn) ratio of the precursor has enabled precise control of the crystalline phase in the form of kesterite, or a newly observed wurtzite structure. Nanocrystals with morphology in the form of spherical, rice-like, or rod-like shapes are obtained over a wide range of compositions (0.5 ≤ Cu/(Zn + Sn) ≤ 1.2). Both the final products and intermediates for each shape exhibit consistent composition and structure, indicating homogenous nucleation and growth of single-phase nanocrystals. Thin films prepared from colloidal nanocrystal suspensions display interesting shape-dependent photoresponse behavior under white light illumination from a solar simulator.

  18. One-Step Synthesis of Monodisperse In-Doped ZnO Nanocrystals

    Directory of Open Access Journals (Sweden)

    Wang QingLing

    2010-01-01

    Full Text Available Abstract A method for the synthesis of high quality indium-doped zinc oxide (In-doped ZnO nanocrystals was developed using a one-step ester elimination reaction based on alcoholysis of metal carboxylate salts. The resulting nearly monodisperse nanocrystals are well-crystallized with typically crystal structure identical to that of wurtzite type of ZnO. Structural, optical, and elemental analyses on the products indicate the incorporation of indium into the host ZnO lattices. The individual nanocrystals with cubic structures were observed in the 5% In–ZnO reaction, due to the relatively high reactivity of indium precursors. Our study would provide further insights for the growth of doped oxide nanocrystals, and deepen the understanding of doping process in colloidal nanocrystal syntheses.

  19. Time Resolved Nucleation and Growth of Monodisperse FeOOH Nanoparticles Observed in situ

    Science.gov (United States)

    Legg, B. A.; Zhu, M.; Zhang, H.; Waychunas, G.; Banfield, J. F.

    2012-12-01

    The nucleation and growth of oxide minerals from aqueous solution is a poorly understood process. Complexities such as two-stage precipitation, phase transformation, and hydrolysis often inhibit simple interpretation. In this study, we track the thermally induced nucleation and growth of akaganeite (β-FeOOH) nanoparticles from FeCl3 solutions, using in situ time resolved small angle x-ray scattering (SAXS) and transmission electron microscopy (TEM). Variations in reaction temperature (from 37 deg C to 80 deg C) and FeCl3 concentration (from 5 mM to 800 mM) produce systematic changes in nucleation rate, growth rate, particle size distribution, and aspect ratio. Low FeCl3 concentrations and high temperatures lead to formation of very small particles via rapid nucleation. (FeCl3 solutions are actually more supersaturated with respect to akaganeite when concentrations are low, due to the acid-base chemistry of ferric iron.) Increasing the FeCl3 concentration leads to large, highly monodisperse particles via size focused growth. Suspensions of highly monodisperse, elongated particles are found to self-organize into two dimensional colloidal crystals. The well-controlled growth processes in this system make it possible to conduct detailed kinetic modeling, and determine how both nucleation and growth rate respond to changes in the experimental conditions.

  20. The hydrocarbon sphere

    Energy Technology Data Exchange (ETDEWEB)

    Mandev, P.

    1984-01-01

    The hydrocarbon sphere is understood to be the area in which hydrocarbon compounds are available. It is believed that the lower boundary on the hydrocarbon sphere is most probably located at a depth where the predominant temperatures aid in the destruction of hydrocarbons (300 to 400 degrees centigrade). The upper limit on the hydrocarbon sphere obviously occurs at the earth's surface, where hydrocarbons oxidize to H20 and CO2. Within these ranges, the occurrence of the hydrocarbon sphere may vary from the first few hundred meters to 15 kilometers or more. The hydrocarbon sphere is divided into the external (mantle) sphere in which the primary gas, oil and solid hydrocarbon fields are located, and the internal (metamorphic) sphere containing primarily noncommercial accumulations of hydrocarbon gases and solid carbon containing compounds (anthraxilite, shungite, graphite, etc.) based on the nature and scale of hydrocarbon compound concentrations (natural gas, oil, maltha, asphalt, asphaltite, etc.).

  1. Rheological properties of Cubic colloidal suspensions

    Science.gov (United States)

    Boromand, Arman; Maia, Joao

    2016-11-01

    Colloidal and non-colloidal suspensions are ubiquitous in many industrial application. There are numerous studies on these systems to understand and relate their complex rheological properties to their microstructural evolution under deformation. Although most of the experimental and simulation studies are centered on spherical particles, in most of the industrial applications the geometry of the colloidal particles deviate from the simple hard sphere and more complex geometries exist. Recent advances in microfabrication paved the way to fabricate colloidal particles with complex geometries for applications in different areas such as drug delivery where the fundamental understanding of their dynamics has remained unexplored. In this study, using dissipative particle dynamics, we investigate the rheological properties of cubic (superball) particles which are modeled as the cluster of core-modified DPD particles. Explicit representation of solvent particles in the DPD scheme will conserve the full hydrodynamic interactions between colloidal particles. Rheological properties of these cubic suspensions are investigated in the dilute and semi-dilute regimes. The Einstein and Huggins coefficients for these particles with different superball exponent will be calculate which represent the effect of single particle's geometry and multibody interactions on viscosity, respectively. The response of these suspensions is investigated under simple shear and oscillatory shear where it is shown that under oscillation these particles tend to form crystalline structure giving rise to stronger shear-thinning behavior recently measured experimentally.

  2. 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...

  3. Equilibrium theory of the hard sphere fluid and glasses in the metastable regime up to jamming. II. Structure and application to hopping dynamics

    Science.gov (United States)

    Jadrich, Ryan; Schweizer, Kenneth S.

    2013-08-01

    Building on the equation-of-state theory of Paper I, we construct a new thermodynamically consistent integral equation theory for the equilibrium pair structure of 3-dimensional monodisperse hard spheres applicable up to the jamming transition. The approach is built on a two Yukawa generalized mean spherical approximation closure for the direct correlation function (DCF) beyond contact that reproduces the exact contact value of the pair correlation function and isothermal compressibility. The detailed construction of the DCF is guided by the desire to capture its distinctive features as jamming is approached. Comparison of the theory with jamming limit simulations reveals good agreement for many, but not all, of the key features of the pair correlation function. The theory is more accurate in Fourier space where predictions for the structure factor and DCF are accurate over a wide range of wavevectors from significantly below the first cage peak to very high wavevectors. New features of the equilibrium pair structure are predicted for packing fractions below jamming but well above crystallization. For example, the oscillatory DCF decays very slowly at large wavevectors for high packing fractions as a consequence of the unusual structure of the radial distribution function at small separations. The structural theory is used as input to the nonlinear Langevin equation theory of activated dynamics, and calculations of the alpha relaxation time based on single particle hopping are compared to recent colloid experiments and simulations at very high volume fractions.

  4. Synthesis of monodisperse crosslinked polystyrene microspheres

    Institute of Scientific and Technical Information of China (English)

    Jiang Kai; Chen Sheng-Li; Dong Peng; Liu Renxiao

    2008-01-01

    Monodisperse crosslinked polystyrene (CPS) particles were prepared through the normal emulsion polymerization method by adding crosslinker-divinylbenzene (DVB) into the reaction system after polystyrene (PS) particles grew to ~80% of the final size. When the amount of crosslinker DVB added was less than 6.17 wt% based on styrene, the prepared CPS particles were spherical and uniform and the size of the CPS particles could be predicted through the normal emulsion method. The glass transition temperature (Tg) of the prepared CPS particles was higher than that of un-crosslinked PS particles and, the more crosslinker that was added, the higher the Tg of CPS Particles. The prepared CPS particles had strong resistance to organic solvents.

  5. Monodisperse microdroplet generation and stopping without coalescence

    Energy Technology Data Exchange (ETDEWEB)

    Beer, Neil Reginald

    2016-02-23

    A system for monodispersed microdroplet generation and trapping including providing a flow channel in a microchip; producing microdroplets in the flow channel, the microdroplets movable in the flow channel; providing carrier fluid in the flow channel using a pump or pressure source; controlling movement of the microdroplets in the flow channel and trapping the microdroplets in a desired location in the flow channel. The system includes a microchip; a flow channel in the microchip; a droplet maker that generates microdroplets, the droplet maker connected to the flow channel; a carrier fluid in the flow channel, the carrier fluid introduced to the flow channel by a source of carrier fluid, the source of carrier fluid including a pump or pressure source; a valve connected to the carrier fluid that controls flow of the carrier fluid and enables trapping of the microdroplets.

  6. 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.

  7. Coupling between bulk- and surface chemistry in suspensions of charged colloids

    Science.gov (United States)

    Heinen, M.; Palberg, T.; Löwen, H.

    2014-03-01

    The ionic composition and pair correlations in fluid phases of realistically salt-free charged colloidal sphere suspensions are calculated in the primitive model. We obtain the number densities of all ionic species in suspension, including low-molecular weight microions, and colloidal macroions with acidic surface groups, from a self-consistent solution of a coupled physicochemical set of nonlinear algebraic equations and non-mean-field liquid integral equations. Here, we study suspensions of colloidal spheres with sulfonate or silanol surface groups, suspended in demineralized water that is saturated with carbon dioxide under standard atmosphere. The only input required for our theoretical scheme are the acidic dissociation constants pKa, and effective sphere diameters of all involved ions. Our method allows for an ab initio calculation of colloidal bare and effective charges, at high numerical efficiency.

  8. Event Driven Langevin simulations of Hard Spheres

    CERN Document Server

    Scala, Antonio

    2011-01-01

    The blossoming of interest in colloids and nano-particles has given renewed impulse to the study of hard-body systems. In particular, hard spheres have become a real test system for theories and experiments. It is therefore necessary to study the complex dynamics of such systems in presence of a solvent; disregarding hydrodynamic interactions, the simplest model is the Langevin equation. Unfortunately, standard algorithms for the numerical integration of the Langevin equation require that interactions are slowly varying during an integration timestep. This in not the case for hard-body systems, where there is no clearcut between the correlation time of the noise and the timescale of the interactions. Starting first from a splitting of the Fokker-Plank operator associated with the Langevin dynamics, and then from an approximation of the two-body Green's function, we introduce and test two new algorithms for the simulation of the Langevin dynamics of hard-spheres.

  9. Thermodiffusion of charged colloids: single-particle diffusion.

    Science.gov (United States)

    Dhont, Jan K G; Wiegand, S; Duhr, S; Braun, D

    2007-02-13

    An expression for the single-particle thermal diffusion coefficient of a charged colloidal sphere is derived on the basis of force balance on the Brownian time scale in combination with thermodynamics. It is shown that the single-particle thermal diffusion coefficient is related to the temperature dependence of the reversible work necessary to build the colloidal particle, including the core, the solvation layer, and the electrical double layer. From this general expression, an explicit expression for the contribution of the electrical double layer to the single-particle thermal diffusion coefficient is derived in terms of the surface charge density of the colloidal sphere, the electrostatic screening length, and its core radius, to within the Debye-Hückel approximation. This result is shown to explain experimental data, for both thin and thick double layers. In addition, a comparison with other theories is made.

  10. Colloids and Nucleation

    Science.gov (United States)

    Ackerson, Bruce

    1997-01-01

    The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range

  11. Preparation of monodisperse, superparamagnetic, luminescent, and multifunctional PGMA microspheres with amino-groups

    Institute of Scientific and Technical Information of China (English)

    WANG WeiCai; ZHANG Qi; ZHANG BingBo; LI DeNa; DONG XiaoQing; ZHANG Lei; CHANG Jin

    2008-01-01

    Micron-sized, monodisperse, superparamagnetic, luminescent composite poly(glycidyl methacrylate) (PGMA) microspheres with functional amino-groups were successfully synthesized in this study. The process of preparation was as follows: preparation of monodisperse poly(glycidyl methacrylate) mi-crospheres by dispersion polymerization method; modification of poly(glycidyl methacrylate) micro-spheres with ethylene diamine to form amino-groups; impregnation of iron ions (Fe2+ and Fe3+) inside the microspheres and subsequently precipitating them with ammonium hydroxide to form magnetite (Fe3O,4>) nanoparticles within the polymer microspheres; infusion of CdSe/CdS core-shell quantum dots (QDs) into magnetic polymer microspheres. Scanning electron microscopy (SEM) was used to char-acterize surface morphology and size distribution of composite microspheres. The average size of mi-crospheres was 1.42μm with a size variation of 3.8%, The composite microspheres were bright enough and easily observed using a conventional fluorescence microscope, The composite microspheres were easily separated from solution by magnetic decantation using a permanent magnet. The new multi-functional composite microspheres are promising to be used in a variety of bioanalytical assays in-volving luminescence detection and magnetic separation.

  12. Jammed lattice sphere packings

    OpenAIRE

    Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore

    2013-01-01

    We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a...

  13. 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.

  14. DISE: directed sphere exclusion.

    Science.gov (United States)

    Gobbi, Alberto; Lee, Man-Ling

    2003-01-01

    The Sphere Exclusion algorithm is a well-known algorithm used to select diverse subsets from chemical-compound libraries or collections. It can be applied with any given distance measure between two structures. It is popular because of the intuitive geometrical interpretation of the method and its good performance on large data sets. This paper describes Directed Sphere Exclusion (DISE), a modification of the Sphere Exclusion algorithm, which retains all positive properties of the Sphere Exclusion algorithm but generates a more even distribution of the selected compounds in the chemical space. In addition, the computational requirement is significantly reduced, thus it can be applied to very large data sets.

  15. Advanced Colloids Experiment (ACE) Science Overview

    Science.gov (United States)

    Meyer, William V.; Sicker, Ronald J.; Chiaramonte, Francis P.; Luna, Unique J.; Chaiken, Paul M.; Hollingsworth, Andrew; Secanna, Stefano; Weitz, David; Lu, Peter; Yodh, Arjun; hide

    2013-01-01

    The Advanced Colloids Experiment is being conducted on the International Space Station (ISS) using the Light Microscopy Module (LMM) in the Fluids Integrated Rack (FIR). Work to date will be discussed and future plans and opportunities will be highlighted. The LMM is a microscope facility designed to allow scientists to process, manipulate, and characterize colloidal samples in micro-gravity where the absence of gravitational settling and particle jamming enables scientists to study such things as:a.The role that disordered and ordered-packing of spheres play in the phase diagram and equation of state of hard sphere systems,b.crystal nucleation and growth, growth instabilities, and the glass transition, c.gelation and phase separation of colloid polymer mixtures,d.crystallization of colloidal binary alloys,e.competition between crystallization and phase separation,f.effects of anisotropy and specific interactions on packing, aggregation, frustration and crystallization,g.effects of specific reversible and irreversible interactions mediated in the first case by hybridization of complementary DNA strands attached to separate colloidal particles,h.Lock and key interactions between colloids with dimples and spheres which match the size and shape of the dimples,i.finding the phase diagrams of isotropic and interacting particles,j.new techniques for complex self-assembly including scenarios for self-replication, k.critical Casimir forces,l.biology (real and model systems) in microgravity,m.etc. By adding additional microscopy capabilities to the existing LMM, NASA will increase the tools available for scientists that fly experiments on the ISS enabling scientists to observe directly what is happening at the particle level. Presently, theories are needed to bridge the gap between what is being observed (at a macroscopic level when photographing samples) with what is happening at a particle (or microscopic) level. What is happening at a microscopic level will be directly

  16. Dynamic equivalences in the hard-sphere dynamic universality class.

    Science.gov (United States)

    López-Flores, Leticia; Ruíz-Estrada, Honorina; Chávez-Páez, Martín; Medina-Noyola, Magdaleno

    2013-10-01

    We perform systematic simulation experiments on model systems with soft-sphere repulsive interactions to test the predicted dynamic equivalence between soft-sphere liquids with similar static structure. For this we compare the simulated dynamics (mean squared displacement, intermediate scattering function, α-relaxation time, etc.) of different soft-sphere systems, between them and with the hard-sphere liquid. We then show that the referred dynamic equivalence does not depend on the (Newtonian or Brownian) nature of the microscopic laws of motion of the constituent particles, and hence, applies independently to colloidal and to atomic simple liquids. Finally, we verify another more recently proposed dynamic equivalence, this time between the long-time dynamics of an atomic liquid and its corresponding Brownian fluid (i.e., the Brownian system with the same interaction potential).

  17. Theory of dynamic arrest in colloidal mixtures.

    Science.gov (United States)

    Juárez-Maldonado, R; Medina-Noyola, M

    2008-05-01

    We present a first-principles theory of dynamic arrest in colloidal mixtures based on the multicomponent self-consistent generalized Langevin equation theory of colloid dynamics [M. A. Chávez-Rojo and M. Medina-Noyola, Phys. Rev. E 72, 031107 (2005); M. A. Chávez-Rojo and M. Medina-Noyola, Phys. Rev. E76, 039902 (2007)]. We illustrate its application with a description of dynamic arrest in two simple model colloidal mixtures: namely, hard-sphere and repulsive Yukawa binary mixtures. Our results include observation of the two patterns of dynamic arrest, one in which both species become simultaneously arrested and the other involving the sequential arrest of the two species. The latter case gives rise to mixed states in which one species is arrested while the other species remains mobile. We also derive the ("bifurcation" or fixed-point") equations for the nonergodic parameters of the system, which takes the surprisingly simple form of a system of coupled equations for the localization length of the particles of each species. The solution of this system of equations indicates unambiguously which species is arrested (finite localization length) and which species remains ergodic (infinite localization length). As a result, we are able to draw the entire ergodic-nonergodic phase diagram of the binary hard-sphere mixture.

  18. 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.

  19. A Study of Multiple Refractive Scattering of Monoenergetic X-Rays from Ensembles of Monodisperse Spheres

    CERN Document Server

    Khromova, Anastasiya

    2010-01-01

    A Monte Carlo program based on a three dimensional vector approach was developed to model multiple refractive scattering of X-ray photons in objects with a fine structure. A particular interest was paid to the investigation of lung tissue. Alveoli are low contrast and low absorbing structures. Hence, they are not visible in the conventional radiography which is based on the changes in the absorption arising from density differences and from variation in the thickness and composition of the object. Another possibility to image fine structure objects is to use the phase imaging techniques. As known, the phase change constant delta at low energies (15-30 keV) is 1000 times larger than the absorption constant beta. The Diffraction Enhance Imaging (DEI) technique is one of the recent phase sensitive techniques based on the use of an analyzer crystal placed between the sample and the detector.

  20. A computer simulation investigation into the stability of the AB2 superlattice in a binary hard sphere system

    NARCIS (Netherlands)

    Eldridge, M.D.; Madden, P.A.; Frenkel, D.

    1993-01-01

    The thermodynamic stability of the binary hard-sphere AB2 superlattice structure has been confirmed by means of computer simulations. This is consistent with the results of experimental studies of suspensions of hard-sphere colloidal particles. A fit of the Helmholtz free energy surface for the regi

  1. MINIMAL IMMERSIONS OF SPHERES INTO SPHERES

    Science.gov (United States)

    Do Carmo, Manfredo P.; Wallach, Nolan R.

    1969-01-01

    In this paper we announce a qualitative description of an important class of closed n-dimensional submanifolds of the m-dimensional sphere, namely, those which locally minimize the n-area in the same way that geodesics minimize the arc length and are themselves locally n-spheres of constant radius r; those r that may appear are called admissible. It is known that for n = 2 each admissible r determines a unique element of the above class. The main result here is that for each n ≥ 3 and each admissible r ≥ [unk]8 there exists a continuum of distinct such submanifolds. PMID:16591771

  2. Interface area transport of monodispersed spherical particulates

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Chong H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-08-05

    We present an interface area transport model required in tracking of mass, momentum, and energy exchange between dispersed and background materials. The basic transport equation has been rigorously derived from the volume fraction evolution equation. Interface area changes due to mass transport and local compression/expansion are included. The model is then simplified for the case in which the dispersed phase is composed of spheres of locally uniform size. A procedure for calculating advective flux with interface reconstruction has been suggested.

  3. Facile Method for Preparation of Silica Coated Monodisperse Superparamagnetic Microspheres

    Directory of Open Access Journals (Sweden)

    Xuan-Hung Pham

    2016-01-01

    Full Text Available This paper presents a facile method for preparation of silica coated monodisperse superparamagnetic microsphere. Herein, monodisperse porous polystyrene-divinylbenzene microbeads were prepared by seeded emulsion polymerization and subsequently sulfonated with acetic acid/H2SO4. The as-prepared sulfonated macroporous beads were magnetized in presence of Fe2+/Fe3+ under alkaline condition and were subjected to silica coating by sol-gel process, providing water compatibility, easily modifiable surface form, and chemical stability. FE-SEM, TEM, FT-IR, and TGA were employed to characterize the silica coated monodisperse magnetic beads (~7.5 μm. The proposed monodisperse magnetic beads can be used as mobile solid phase particles candidate for protein and DNA separation.

  4. Bulk synthesis of polymer-inorganic colloidal clusters.

    Science.gov (United States)

    Perro, Adeline; Manoharan, Vinothan N

    2010-12-21

    We describe a procedure to synthesize colloidal clusters with polyhedral morphologies in high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. We show that the synthesis initially used for silica-polystyrene hybrid clusters can be generalized to create clusters from other inorganic and polymer particles. We also show that high yields of particular morphologies can be obtained by precise control of the inorganic seed particle size, a finding that can be explained using a hard-sphere packing model. These clusters can be further chemically modified for a variety of applications. Introducing a cross-linker leads to colloidal clusters that can be index matched in an appropriate solvent, allowing them to be used for particle tracking or optical studies of colloidal self-assembly. Also, depositing a thin silica layer on these colloids allows the surface properties to be controlled using silane chemistry.

  5. 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.

  6. Silicon and Carbon Nanocomposite Spheres with Enhanced Electrochemical Performance for Full Cell Lithium Ion Batteries

    Science.gov (United States)

    Wang, Wei; Favors, Zachary; Li, Changling; Liu, Chueh; Ye, Rachel; Fu, Chengyin; Bozhilov, Krassimir; Guo, Juchen; Ozkan, Mihrimah; Ozkan, Cengiz S.

    2017-01-01

    Herein, facile synthesis of monodisperse silicon and carbon nanocomposite spheres (MSNSs) is achieved via a simple and scalable surface-protected magnesiothermic reduction with subsequent chemical vapor deposition (CVD) process. Li-ion batteries (LIBs) were fabricated to test the utility of MSNSs as an anode material. LIB anodes based on MSNSs demonstrate a high reversible capacity of 3207 mAh g−1, superior rate performance, and excellent cycling stability. Furthermore, the performance of full cell LIBs was evaluated by using MSNS anode and a LiCoO2 cathode with practical electrode loadings. The MSNS/LiCoO2 full cell demonstrates high gravimetric energy density in the order of 850 Wh L−1 with excellent cycling stability. This work shows a proof of concept of the use of monodisperse Si and C nanocomposite spheres toward practical lithium-ion battery applications. PMID:28322285

  7. Study on Osmotic Pressure and Liquid-Liquid Equilibria for Micelle, Colloid and Microemulsion Systems by Yukawa Potential

    Institute of Scientific and Technical Information of China (English)

    FU,Dong(付东); LU,Jiu-Fang(陆九芳); WU,Wei(吴畏); Li,Yi-Gui(李以圭)

    2004-01-01

    An equation of state (EOS) was established to study the osmotic pressure and liquid-liquid equilibria for micelle,colloid and microemulsion systems. The Carnahan-Starling equation was used for the hard sphere repulsion. The Yukawa potential was used to describe both the attractive dispersion and the double-layer repulsion. By using the established EOS, the osmotic pressures for charged colloid, uncharged micelle, uncharged and weakly charged microemuslion, the phase equilibria for uncharged micelle and charged colloid systems were studied.

  8. Variable dislocation widths in colloidal crystals of soft thermosensitive spheres

    NARCIS (Netherlands)

    Hilhorst, J.; Petukhov, A.V.

    2011-01-01

    Themagnetic and structural properties of a cobalt inverse opal-like crystal have been studied by a combination of complementary techniques ranging from polarized neutron scattering and superconducting quantum interference device (SQUID) magnetometry to x-ray diffraction. Microradian small-angle x-ra

  9. Startup of electrophoresis in a suspension of colloidal spheres.

    Science.gov (United States)

    Chiang, Chia C; Keh, Huan J

    2015-12-01

    The transient electrophoretic response of a homogeneous suspension of spherical particles to the step application of an electric field is analyzed. The electric double layer encompassing each particle is assumed to be thin but finite, and the effect of dynamic electroosmosis within it is incorporated. The momentum equation for the fluid outside the double layers is solved through the use of a unit cell model. Closed-form formulas for the time-evolving electrophoretic and settling velocities of the particles in the Laplace transform are obtained in terms of the electrokinetic radius, relative mass density, and volume fraction of the particles. The time scale for the development of electrophoresis and sedimentation is significantly smaller for a suspension with a higher particle volume fraction or a smaller particle-to-fluid density ratio, and the electrophoretic mobility at any instant increases with an increase in the electrokinetic particle radius. The transient electrophoretic mobility is a decreasing function of the particle volume fraction if the particle-to-fluid density ratio is relatively small, but it may increase with an increase in the particle volume fraction if this density ratio is relatively large. The particle interaction effect in a suspension on the transient electrophoresis is much weaker than that on the transient sedimentation of the particles.

  10. 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.

  11. ORGANIZATION IN CONTEMPORARY PUBLIC SPHERE

    National Research Council Canada - National Science Library

    Rosemarie HAINES

    2013-01-01

    The critical analysis of Habermas’ Public Sphere Theory and the comparative undertaking to the current day enables us to assert that in contemporary society, public sphere is no longer a political public sphere, this dimension being...

  12. Theory of asymmetric nonadditive binary hard-sphere mixtures.

    Science.gov (United States)

    Roth, R; Evans, R; Louis, A A

    2001-11-01

    It is shown that the formal procedure of integrating out the degrees of freedom of the small spheres in a binary hard-sphere mixture works equally well for nonadditive as it does for additive mixtures. For highly asymmetric mixtures (small size ratios) the resulting effective Hamiltonian of the one-component fluid of big spheres, which consists of an infinite number of many-body interactions, should be accurately approximated by truncating after the term describing the effective pair interaction. Using a density functional treatment developed originally for additive hard-sphere mixtures the zero, one, and two-body contribution to the effective Hamiltonian are determined. It is demonstrated that even small degrees of positive or negative nonadditivity have significant effect on the shape of the depletion potential. The second virial coefficient B2, corresponding to the effective pair interaction between two big spheres, is found to be a sensitive measure of the effects of nonadditivity. The variation of B2 with the density of the small spheres shows significantly different behavior for additive, slightly positive and slightly negative nonadditive mixtures. Possible repercussions of these results for the phase behavior of binary hard-sphere mixtures are discussed and it is suggested that measurements of B2 might provide a means of determining the degree of nonadditivity in real colloidal mixtures.

  13. 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.

  14. 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.

  15. 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...

  16. SPHERES National Lab Facility

    Science.gov (United States)

    Benavides, Jose

    2014-01-01

    SPHERES is a facility of the ISS National Laboratory with three IVA nano-satellites designed and delivered by MIT to research estimation, control, and autonomy algorithms. Since Fall 2010, The SPHERES system is now operationally supported and managed by NASA Ames Research Center (ARC). A SPHERES Program Office was established and is located at NASA Ames Research Center. The SPHERES Program Office coordinates all SPHERES related research and STEM activities on-board the International Space Station (ISS), as well as, current and future payload development. By working aboard ISS under crew supervision, it provides a risk tolerant Test-bed Environment for Distributed Satellite Free-flying Control Algorithms. If anything goes wrong, reset and try again! NASA has made the capability available to other U.S. government agencies, schools, commercial companies and students to expand the pool of ideas for how to test and use these bowling ball-sized droids. For many of the researchers, SPHERES offers the only opportunity to do affordable on-orbit characterization of their technology in the microgravity environment. Future utilization of SPHERES as a facility will grow its capabilities as a platform for science, technology development, and education.

  17. Experiment SPHERE status 2008

    Energy Technology Data Exchange (ETDEWEB)

    Shaulov, S.B., E-mail: shaul@sci.lebedev.r [P.N.Lebedev Physical Institute, Russian Academy of Sciences, Leninsky prospect 53, Moscow 119991 (Russian Federation); Besshapov, S.P.; Kabanova, N.V.; Sysoeva, T.I. [P.N.Lebedev Physical Institute, Russian Academy of Sciences, Leninsky prospect 53, Moscow 119991 (Russian Federation); Antonov, R.A.; Anyuhina, A.M.; Bronvech, E.A.; Chernov, D.V.; Galkin, V.I. [Skobeltsyn Institute of Nuclear Physics, Lomonosov State University, Moscow 119992 (Russian Federation); Tkaczyk, W. [Department of Experimental Physics of University of Lodz (Poland); Finger, M. [Karlov University, Prague (Czech Republic); Sonsky, M. [COMPAS Consortium, Turnov (Czech Republic)

    2009-12-15

    The expedition carried out in March, 2008 to Lake Baikal became an important stage in the development of the SPHERE experiment. During the expedition the SPHERE-2 installation was hoisted, for the first time, on a tethered balloon, APA, to a height of 700 m over the lake surface covered with ice and snow. A series of test measurements were made. Preliminary results of the data processing are presented. The next plan of the SPHERE experiment is to begin a set of statistics for constructing the CR spectrum in the energy range 10{sup 16}-10{sup 18} eV.

  18. Jammed lattice sphere packings.

    Science.gov (United States)

    Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore

    2013-12-01

    We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.

  19. Jammed lattice sphere packings

    Science.gov (United States)

    Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore

    2013-12-01

    We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.

  20. Self-assembly of colloids with liquid protrusions.

    Science.gov (United States)

    Kraft, Daniela J; Vlug, Wessel S; van Kats, Carlos M; van Blaaderen, Alfons; Imhof, Arnout; Kegel, Willem K

    2009-01-28

    A facile and flexible synthesis for colloidal molecules with well-controlled shape and tunable patchiness is presented. Cross-linked polystyrene spheres with a liquid protrusion were found to assemble into colloidal molecules by coalescence of the liquid protrusions. Similarly, cross-linked poly(methyl methacrylate) particles carrying a wetting layer assembled into colloidal molecules by coalescence of the wetting layer. Driven by surface energy, a liquid droplet on which the solid spheres are attached is formed. Subsequent polymerization of the liquid yields a wide variety of colloidal molecules as well as colloidosomes with tunable patchiness. Precise control over the topology of the particles has been achieved by changing the amount and nature of the swelling monomer as well as the wetting angle between the liquid and the seed particles. The overall cluster size can be controlled by the seed size as well as the swelling ratio. Use of different swelling monomers and/or particles allows for chemical diversity of the patches and the center. For low swelling ratios assemblies of small numbers of seeds resemble clusters that minimize the second moment of the mass distribution. Assemblies comprised of a large number of colloids are similar to colloidosomes exhibiting elastic strain relief by scar formation.

  1. Rapid enumeration of phage in monodisperse emulsions.

    Science.gov (United States)

    Tjhung, Katrina F; Burnham, Sean; Anany, Hany; Griffiths, Mansel W; Derda, Ratmir

    2014-06-17

    Phage-based detection assays have been developed for the detection of viable bacteria for applications in clinical diagnosis, monitoring of water quality, and food safety. The majority of these assays deliver a positive readout in the form of newly generated progeny phages by the bacterial host of interest. Progeny phages are often visualized as plaques, or holes, in a lawn of bacteria on an agar-filled Petri dish; however, this rate-limiting step requires up to 12 h of incubation time. We have previously described an amplification of bacteriophages M13 inside droplets of media suspended in perfluorinated oil; a single phage M13 in a droplet yields 10(7) copies in 3-4 h. Here, we describe that encapsulation of reporter phages, both lytic T4-LacZ and nonlytic M13, in monodisperse droplets can also be used for rapid enumeration of phage. Compartmentalization in droplets accelerated the development of the signal from the reporter enzyme; counting of "positive" droplets yields accurate enumeration of phage particles ranging from 10(2) to 10(6) pfu/mL. For enumeration of T4-LacZ phage, the fluorescent signal appeared in as little as 90 min. Unlike bulk assays, quantification in emulsion is robust and insensitive to fluctuations in environmental conditions (e.g., temperature). Power-free emulsification using gravity-driven flow in the absence of syringe pumps and portable fluorescence imaging solutions makes this technology promising for use at the point of care in low-resource environments. This droplet-based phage enumeration method could accelerate and simplify point-of-care detection of the pathogens for which reporter bacteriophages have been developed.

  2. Colloidal quantum dot photovoltaics: The effect of polydispersity

    KAUST Repository

    Zhitomirsky, David

    2012-02-08

    The size-effect tunability of colloidal quantum dots enables facile engineering of the bandgap at the time of nanoparticle synthesis. The dependence of effective bandgap on nanoparticle size also presents a challenge if the size dispersion, hence bandgap variability, is not well-controlled within a given quantum dot solid. The impact of this polydispersity is well-studied in luminescent devices as well as in unipolar electronic transport; however, the requirements on monodispersity have yet to be quantified in photovoltaics. Here we carry out a series of combined experimental and model-based studies aimed at clarifying, and quantifying, the importance of quantum dot monodispersity in photovoltaics. We successfully predict, using a simple model, the dependence of both open-circuit voltage and photoluminescence behavior on the density of small-bandgap (large-diameter) quantum dot inclusions. The model requires inclusion of trap states to explain the experimental data quantitatively. We then explore using this same experimentally tested model the implications of a broadened quantum dot population on device performance. We report that present-day colloidal quantum dot photovoltaic devices with typical inhomogeneous linewidths of 100-150 meV are dominated by surface traps, and it is for this reason that they see marginal benefit from reduction in polydispersity. Upon eliminating surface traps, achieving inhomogeneous broadening of 50 meV or less will lead to device performance that sees very little deleterious impact from polydispersity. © 2012 American Chemical Society.

  3. Rapid fabrication of large area binary polystyrene colloidal crystals

    Science.gov (United States)

    Luo, Chun-Li; Yang, Rui-Xia; Yan, Wei-Guo; Zhao, Jian; Yang, Guang-Wu; Jia, Guo-Zhi

    2016-07-01

    Binary colloidal crystals (BCCs) possess great potentials in tuning material and optical properties. In this paper, the combination of interface transferred method and spin-coating method is used to fabricate BCCs with different patterns via controlling the size ratio of small (S) to large (L) colloidal spheres and the spin speeds. It is found that BCCs formed LS2, LS4 and LS6 by changing the size ratio. In addition, there are some new and complicated structures, such as LS12, Janus arrays, formed at the low spin speed. This simple assembly method has potential to allow for the creation of optical metmaterials and the plasmonic structures with chiral optical properties.

  4. 氘代聚苯乙烯胶体晶体的制备及光学性质研究%Fabrication and optical properties of deuterated polystyrene colloidal crystals

    Institute of Scientific and Technical Information of China (English)

    严鸿维; 张林; 吕海兵; 袁晓东; 任洪波

    2012-01-01

    以水作为介质合成了高度单分散的氘代聚苯乙烯微球,并利用垂直沉积法制备了高质量的氘代聚苯乙烯胶体晶体.傅立叶变换红外光谱清楚地表明氘代苯乙烯单体发生了聚合反应;扫描电镜表面分析展示出胶体微球的高度有序排列,断面分析表明氘代聚苯乙烯胶体晶体为面心立方结构;光学透射谱显示出氘代聚苯乙烯胶体晶体的高次布拉格衍射特征,通过和理论计算的能带结构对比,进一步证实了氘代聚苯乙烯胶体晶体为面心立方结构;变角度光学透射谱测量显示,随着入射角的增大,(111)面的衍射峰蓝移,而(200)和(220)面的衍射峰发生红移.%Highly monodisperse deuterated polystyrene colloidal spheres were synthesized in water medium. High-quality deuterated polystyrene colloidal crystals were fabricated by vertical deposition method. It was clearly shown that deuterated styrene monomers had generated a polymerization reaction through Fourier transform infrared spectroscopy. Highly ordered arrangement of colloidal microspheres was confirmed by scanning e-lectron microscopy, and it was considered to be face-centered cubic structure by cross-sectional image analysis. The transmission spectra of deuterated polystyrene colloidal crystals exhibited some characterization of high-order Bragg diffraction, which further confirmed the face-centered cubic close-packed structure of deuterated polystyrene colloidal crystals as compared to the calculated band structure. Angle resolved transmission spectra showed the diffraction peak of (111) plane was blueshifted, while the diffraction peaks of (200) and (220) planes were both redshifted as increasing the incident angles.

  5. Colloidal plasmonic back reflectors for light trapping in solar cells

    Science.gov (United States)

    Mendes, Manuel J.; Morawiec, Seweryn; Simone, Francesca; Priolo, Francesco; Crupi, Isodiana

    2014-04-01

    A novel type of plasmonic light trapping structure is presented in this paper, composed of metal nanoparticles synthesized in colloidal solution and self-assembled in uniform long-range arrays using a wet-coating method. The high monodispersion in size and spherical shape of the gold colloids used in this work allows a precise match between their measured optical properties and electromagnetic simulations performed with Mie theory, and enables the full exploitation of their collective resonant plasmonic behavior for light-scattering applications. The colloidal arrays are integrated in plasmonic back reflector (PBR) structures aimed for light trapping in thin film solar cells. The PBRs exhibit high diffuse reflectance (up to 75%) in the red and near-infrared spectrum, which can pronouncedly enhance the near-bandgap photocurrent generated by the cells. Furthermore, the colloidal PBRs are fabricated by low-temperature (<120 °C) processes that allow their implementation, as a final step of the cell construction, in typical commercial thin film devices generally fabricated in a superstrate configuration.

  6. Polydispersity and gelation in concentrated colloids with competing interactions.

    Science.gov (United States)

    Zhang, Tian Hui; Kuipers, Bonny W M; Tian, Wen-de; Groenewold, Jan; Kegel, Willem K

    2015-01-14

    In colloids with competing short-range attractions and long-range repulsions, microcrystalline gels are experimentally formed under conditions where computer simulations point to a lamellar phase as the ground state. Here, upon applying a low-frequency alternating electric field, we bring the system from an initial gel state to a columnar-like state. While molecular dynamics simulations on monodisperse colloids reveal that a columnar structure spontaneously evolves towards a lamellar phase, the columnar-like state in experiments relaxes back to the initial disordered gel state once the electric field is switched off. Similarly, a columnar phase in molecular dynamics simulations decomposes into finite-size crystalline clusters as the relative polydispersity of the colloids is around 1.0%. We conclude that the experimentally observed melting of the columnar structure is driven by polydispersity. Moreover, further simulations reveal that the critical polydispersity required to destabilize a long-range ordered structure increases with the attraction range, pointing to the possibility of observing periodic structures in experiments if the attraction range is sufficiently long compared to the polydispersity of the colloids.

  7. Image method for induced surface charge from many-body system of dielectric spheres

    Science.gov (United States)

    Qin, Jian; de Pablo, Juan J.; Freed, Karl F.

    2016-09-01

    Charged dielectric spheres embedded in a dielectric medium provide the simplest model for many-body systems of polarizable ions and charged colloidal particles. We provide a multiple scattering formulation for the total electrostatic energy for such systems and demonstrate that the polarization energy can be rapidly evaluated by an image method that generalizes the image methods for conducting spheres. Individual contributions to the total electrostatic energy are ordered according to the number of polarized surfaces involved, and each additional surface polarization reduces the energy by a factor of (a/R)3ɛ, where a is the sphere radius, R the average inter-sphere separation, and ɛ the relevant dielectric mismatch at the interface. Explicit expressions are provided for both the energy and the forces acting on individual spheres, which can be readily implemented in Monte Carlo and molecular dynamics simulations of polarizable charged spheres, thereby avoiding costly computational techniques that introduce a surface charge distribution that requires numerical solution.

  8. 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

  9. Affine Sphere Relativity

    Science.gov (United States)

    Minguzzi, E.

    2016-11-01

    We investigate spacetimes whose light cones could be anisotropic. We prove the equivalence of the structures: (a) Lorentz-Finsler manifold for which the mean Cartan torsion vanishes, (b) Lorentz-Finsler manifold for which the indicatrix (observer space) at each point is a convex hyperbolic affine sphere centered on the zero section, and (c) pair given by a spacetime volume and a sharp convex cone distribution. The equivalence suggests to describe (affine sphere) spacetimes with this structure, so that no algebraic-metrical concept enters the definition. As a result, this work shows how the metric features of spacetime emerge from elementary concepts such as measure and order. Non-relativistic spacetimes are obtained replacing proper spheres with improper spheres, so the distinction does not call for group theoretical elements. In physical terms, in affine sphere spacetimes the light cone distribution and the spacetime measure determine the motion of massive and massless particles (hence the dispersion relation). Furthermore, it is shown that, more generally, for Lorentz-Finsler theories non-differentiable at the cone, the lightlike geodesics and the transport of the particle momentum over them are well defined, though the curve parametrization could be undefined. Causality theory is also well behaved. Several results for affine sphere spacetimes are presented. Some results in Finsler geometry, for instance in the characterization of Randers spaces, are also included.

  10. Chinese Armillary Spheres

    Science.gov (United States)

    Sun, Xiaochun

    The armillary sphere was perhaps the most important type of astronomical instrument in ancient China. It was first invented by Luoxia Hong in the first century BC. After Han times, the structure of the armillary sphere became increasingly sophisticated by including more and more rings representing various celestial movements as recognized by the Chinese astronomers. By the eighth century, the Chinese armillary sphere consisted of three concentric sets of rings revolving on the south-north polar axis. The relative position of the rings could be adjusted to reflect the precession of the equinoxes and the regression of the Moon's nodes along the ecliptic. To counterbalance the defect caused by too many rings, Guo Shoujing from the late thirteenth century constructed the Simplified Instruments which reorganized the rings of the armillary sphere into separate instruments for measuring equatorial coordinates and horizontal coordinates. The armillary sphere was still preserved because it was a good illustration of celestial movements. A fifteenth-century replica of Guo Shoujing's armillary sphere still exists today.

  11. In situ monitoring of structural changes during colloidal self-assembly.

    Science.gov (United States)

    Koh, Yaw Koon; Wong, Chee Cheong

    2006-01-31

    Reflectance spectroscopy is utilized to monitor structural changes during the self-assembly of a monodisperse colloidal system at the meniscus of a sessile drop on an inert substrate. Treating the ordered colloidal structure as a photonic crystal is equivalent to monitoring the changes in the photonic band gap (PBG) as the colloidal system self-assembles heterogeneously into a crystal through solvent evaporation in ambient conditions. Using a modified Bragg's law model of the photonic crystal, we can trace the structural evolution of the self-assembling colloidal system. After a certain induction period, a face-centered cubic (FCC) structure emerges, albeit with a lattice parameter larger than that of a true close-packed structure. This FCC structure is maintained while the lattice parameter shrinks continuously with further increase in the colloidal concentration due to drying. When the structure reaches a lattice parameter 1.09 times the size of that of a true close-packed structure, it undergoes an abrupt decrease in lattice spacing, apparently similar to those reported for lattice-distortive martensitic transformations. This abrupt final lattice shrinkage agrees well with the estimated Debye screening length of the electric double layer of charged colloids and could be the fundamental reason behind the cracking commonly seen in colloidal crystals.

  12. Strain-responsive structural colored elastomers by fixing colloidal crystal assembly.

    Science.gov (United States)

    Ito, Tatsunori; Katsura, Chihiro; Sugimoto, Hideki; Nakanishi, Eiji; Inomata, Katsuhiro

    2013-11-12

    Colloidal crystal assembly film was prepared by using monodispersed colloidal particles of cross-linked random copolymer of methyl methacrylate and ethyl acrylate prepared by soap-free emulsion polymerization. The colloidal crystal film exhibited structural color when swollen with ethyl acrylate monomer. The structural color was maintained even after polymerization of the swelling monomer and cross-linker, suggesting the colloidal crystalline order was successfully fixed and embedded in the matrix of poly(ethyl acrylate) elastomer. Stretching deformation of the structural colored elastomer induced a sensitive change to shorter wavelength color. Peak wavelength of the UV-vis absorption spectrum of the stretched elastomer revealed an excellent proportional relationship with film thickness. In the swollen colloidal crystal film, ethyl acrylate was absorbed in the colloidal particle; therefore, poly(ethyl acrylate) chain should be penetrating into the colloidal particle after the polymerization of the matrix elastomer. This interpenetrated polymer network structure was considered to be effective for the rubber-like elasticity and sensitive strain-responsive color-changing phenomena of the structural colored elastomer.

  13. Large attractive depletion interactions in soft repulsive-sphere binary mixtures.

    Science.gov (United States)

    Cinacchi, Giorgio; Martínez-Ratón, Yuri; Mederos, Luis; Navascués, Guillermo; Tani, Alessandro; Velasco, Enrique

    2007-12-07

    We consider binary mixtures of soft repulsive spherical particles and calculate the depletion interaction between two big spheres mediated by the fluid of small spheres, using different theoretical and simulation methods. The validity of the theoretical approach, a virial expansion in terms of the density of the small spheres, is checked against simulation results. Attention is given to the approach toward the hard-sphere limit and to the effect of density and temperature on the strength of the depletion potential. Our results indicate, surprisingly, that even a modest degree of softness in the pair potential governing the direct interactions between the particles may lead to a significantly more attractive total effective potential for the big spheres than in the hard-sphere case. This might lead to significant differences in phase behavior, structure, and dynamics of a binary mixture of soft repulsive spheres. In particular, a perturbative scheme is applied to predict the phase diagram of an effective system of big spheres interacting via depletion forces for a size ratio of small and big spheres of 0.2; this diagram includes the usual fluid-solid transition but, in the soft-sphere case, the metastable fluid-fluid transition, which is probably absent in hard-sphere mixtures, is close to being stable with respect to direct fluid-solid coexistence. From these results, the interesting possibility arises that, for sufficiently soft repulsive particles, this phase transition could become stable. Possible implications for the phase behavior of real colloidal dispersions are discussed.

  14. Centrifugation-assisted Assembly of Colloidal Silica into Crack-Free and Transferrable Films with Tunable Crystalline Structures.

    Science.gov (United States)

    Fan, Wen; Chen, Min; Yang, Shu; Wu, Limin

    2015-07-10

    Self-assembly of colloidal particles into colloidal films has many actual and potential applications. While various strategies have been developed to direct the assembly of colloidal particles, fabrication of crack-free and transferrable colloidal film with controllable crystal structures still remains a major challenge. Here we show a centrifugation-assisted assembly of colloidal silica spheres into free-standing colloidal film by using the liquid/liquid interfaces of three immiscible phases. Through independent control of centrifugal force and interparticle electrostatic repulsion, polycrystalline, single-crystalline and quasi-amorphous structures can be readily obtained. More importantly, by dehydration of silica particles during centrifugation, the spontaneous formation of capillary water bridges between particles enables the binding and pre-shrinkage of the assembled array at the fluid interface. Thus the assembled colloidal films are not only crack-free, but also robust and flexible enough to be easily transferred on various planar and curved substrates.

  15. Rheology, microstructure and migration in brownian colloidal suspensions.

    Science.gov (United States)

    Pan, Wenxiao; Caswell, Bruce; Karniadakis, George Em

    2010-01-05

    We demonstrate that suspended spherical colloidal particles can be effectively modeled as single dissipative particle dynamics (DPD) particles provided that the conservative repulsive force is appropriately chosen. The suspension model is further improved with a new formulation, which augments standard DPD with noncentral dissipative shear forces between particles while preserving angular momentum. Using the new DPD formulation we investigate the rheology, microstructure and shear-induced migration of a monodisperse suspension of colloidal particles in plane shear flows (Couette and Poiseuille). Specifically, to achieve a well-dispersed suspension we employ exponential conservative forces for the colloid-colloid and colloid-solvent interactions but keep the conventional linear force for the solvent-solvent interactions. Our simulations yield relative viscosity versus volume fraction predictions in good agreement with both experimental data and empirical correlations. We also compute the shear-dependent viscosity and the first and second normal-stress differences and coefficients in both Couette and Poiseuille flow. Simulations near the close packingvolume-fraction (64%) at low shear rates demonstrate a transition to flow-induced string-like structures of colloidal particles simultaneously with a transition to a nonlinear Couette velocity profile in agreement with experimental observations. After a sufficient increase ofthe shear rate the ordered structure melts into disorder with restoration of the linear velocity profile. Migration effects simulated in Poiseuille flow compare well with experiments and model predictions. The important role of angular momentum and torque in nondilute suspensions is also demonstrated when compared with simulations by the standard DPD, which omits the angular degrees of freedom. Overall, the new method agrees very well with the Stokesian Dynamics method but it seems to have lower computational complexity and is applicable to general

  16. Crystallizing hard-sphere glasses by doping with active particles.

    Science.gov (United States)

    Ni, Ran; Cohen Stuart, Martien A; Dijkstra, Marjolein; Bolhuis, Peter G

    2014-09-21

    Crystallization and vitrification are two different routes to form a solid. Normally these two processes suppress each other, with the glass transition preventing crystallization at high density (or low temperature). This is even true for systems of colloidal hard spheres, which are commonly used as building blocks for novel functional materials with potential applications, e.g. photonic crystals. By performing Brownian dynamics simulations of glassy systems consisting of mixtures of active and passive hard spheres, we show that the crystallization of such hard-sphere glasses can be dramatically promoted by doping the system with small amounts of active particles. Surprisingly, even hard-sphere glasses of packing fraction up to ϕ = 0.635 crystallize, which is around 0.5% below the random close packing at ϕ ≃ 0.64. Our results suggest a novel way of fabricating crystalline materials from (colloidal) glasses. This is particularly important for materials that get easily kinetically trapped in glassy states, and the crystal nucleation hardly occurs.

  17. Depletion potential in hard-sphere mixtures: theory and applications

    Science.gov (United States)

    Roth; Evans; Dietrich

    2000-10-01

    -Oosawa potential. We provide an accurate parametrization of the depletion potential in hard-sphere fluids, which should be useful for effective Hamiltonian studies of phase behavior and colloid structure. Our results for the depletion potential in a hard-sphere system, with a size ratio s=0.0755 chosen to mimic a recent experiment on a colloid-colloid mixture, are compared with the experimental data. Although there is good overall agreement, in particular for the dependence of the oscillations on eta(s), there are some significant differences at high values of eta(s).

  18. 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 .

  19. Controlled assembly of single colloidal crystals using electro-osmotic micro-pumps

    OpenAIRE

    Niu, Ran; Oğuz, Erdal C.; Müller, Hannah; Reinmüller, Alexander; Botin, Denis; Löwen, Hartmut; Palberg, Thomas

    2016-01-01

    We assemble charged colloidal spheres at deliberately chosen locations on a charged unstructured glass substrate utilizing ion exchange based electro-osmotic micro-pumps. Using microscopy, a simple scaling theory and Brownian Dynamics simulations, we systematically explore the control parameters of crystal assembly and the mechanisms through which they depend on the experimental boundary conditions. We demonstrate that crystal quality depends crucially on the assembly distance of the colloids...

  20. 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

  1. Dispersed-nanoparticle loading synthesis for monodisperse Au-titania composite particles and their crystallization for highly active UV and visible photocatalysts.

    Science.gov (United States)

    Sakamoto, Takeshi; Nagao, Daisuke; Noba, Masahiro; Ishii, Haruyuki; Konno, Mikio

    2014-06-24

    Submicrometer-sized amorphous titania spheres incorporating Au nanoparticles (NPs) were prepared in a one-pot synthesis consisting of a sol-gel reaction of titanium(IV) isopropoxide in the presence of chloroauric acid and a successive reduction with sodium borohydride in a mixed solvent of ethanol/acetonitrile. The synthesis was allowed to prepare monodisperse titania spheres that homogeneously incorporated Au NPs with sizes of ca. 7 nm. The Au NP-loaded titania spheres underwent different crystallization processes, including 500 °C calcination in air, high-temperature hydrothermal treatment (HHT), and/or low-temperature hydrothermal treatment (LHT). Photocatalytic experiments were conducted with the Au NP-loaded crystalline titania spheres under irradiation of UV and visible light. A combined process of LHT at 80 °C followed by calcination at 500 °C could effectively crystallize titania spheres maintaining the dispersion state of Au NPs, which led to photocatalytic activity higher than that of commercial P25 under UV irradiation. Under visible light irradiation, the Au NP-titania spheres prepared with a crystallization process of LHT at 80 °C for 6 h showed photocatalytic activity much higher than a commercial product of visible light photocatalyst. Structure analysis of the visible light photocatalysts indicates the importance of prevention of the Au NPs aggregation in the crystallization processes for enhancement of photocatalytic activity.

  2. 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

  3. Spontaneous droplet formation techniques for monodisperse emulsions preparation – Perspectives for food applications

    NARCIS (Netherlands)

    Maan, A.A.; Schroën, C.G.P.H.; Boom, R.M.

    2011-01-01

    Spontaneous droplet formation through Laplace pressure differences is a simple method for making monodisperse emulsions and is claimed to be suited for shear and temperature sensitive products, and those requiring high monodispersity. Techniques belonging to this category include (grooved) microchan

  4. Metal Fe{sup 3+} ions assisted synthesis of highly monodisperse Ag/SiO{sub 2} nanohybrids and their antibacterial activity

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Nianchun; Xue, Feng [College of Material Science and Engineering, South China University of Technology, Guangzhou 510641 (China); Yu, Xiang [Analytical and Testing Center, Jinan University, Guangzhou 510632 (China); Zhou, Huihua [Guangdong East Sunshine Pharmaceutical Co., Ltd., Dongguan 523871 (China); Ding, Enyong, E-mail: eyding@scut.edu.cn [College of Material Science and Engineering, South China University of Technology, Guangzhou 510641 (China)

    2013-02-15

    Graphical abstract: TEM images of the Ag/SiO{sub 2}-2 nanohybrids. The homogeneous and more mono-disperse Ag nanoparticles deposit on SiO{sub 2} spheres. Through this method, Ag nanoparticles are easily formed on the surface of SiO{sub 2} compared to other methods. Highlights: Black-Right-Pointing-Pointer We prepared homogeneous and mono-dispersed Ag/SiO{sub 2}-2 nanohybrids by adding Fe{sup 3+} ions. Black-Right-Pointing-Pointer The Ag/SiO{sub 2}-2 nanohybrids had core(SiO{sub 2})-shell(Ag) structure. Black-Right-Pointing-Pointer The Ag/SiO{sub 2}-2 nanohybrids exhibited excellent antibacterial activity against bacteria. Black-Right-Pointing-Pointer The reaction temperature was lower and the yield of Ag/SiO{sub 2}-2 nanohybrids were higher. - Abstract: Highly monodispersed Ag/SiO{sub 2} nanohybrids with excellent antibacterial property were synthesized by using DMF as a reducing agent and employing an additional redox potential of metal Fe{sup 3+} ion as a catalytic agent. The obtained Ag/SiO{sub 2}-2 nanohybrids of about 240 nm were highly monodispersity and uniformity by adding trace Fe{sup 3+} ions into the reaction which Ag{sup +} reacted with N,N-dimethyl formamide (DMF) at 70 Degree-Sign C. Compared to the conventional techniques, which need long time and high temperature for silica coating of Ag nanoparticles, this new method was capable of synthesizing monodispersed, uniform, high yield Ag/SiO{sub 2} nanohybrids. The electron was transferred from the Fe{sup 2+} ion to the Ag{sup +} ion to accelerate the nucleation of silver nanoparticles. The chemical structures, morphologies and properties of the Ag/SiO{sub 2} nanohybrids were characterized by X-ray diffraction (XRD), (High-resolution, Scanning transmission) transmission electron microscopy (TEM, HRTEM and STEM), and X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy (UV-vis) and test of antibacterial. The results demonstrated that the silver nanoparticles supported on the surface of Si

  5. Nearly Monodispersion CoSm Alloy Nanoparticles Formed by an In-situ Rapid Cooling and Passivating Microfluidic Process

    Directory of Open Access Journals (Sweden)

    Henry Laurence

    2009-01-01

    Full Text Available Abstract An in siturapid cooling and passivating microfluidic processhas been developed for the synthesis of nearly monodispersed cobalt samarium nanoparticles (NPs with tunable crystal structures and surface properties. This process involves promoting the nucleation and growth of NPs at an elevated temperature and rapidly quenching the NP colloids in a solution containing a passivating reagent at a reduced temperature. We have shown that Cobalt samarium NPs having amorphous crystal structures and a thin passivating layer can be synthesized with uniform nonspherical shapes and size of about 4.8 nm. The amorphous CoSm NPs in our study have blocking temperature near 40 K and average coercivity of 225 Oe at 10 K. The NPs also exhibit high anisotropic magnetic properties with a wasp-waist hysteresis loop and a bias shift of coercivity due to the shape anisotropy and the exchange coupling between the core and the thin oxidized surface layer.

  6. Efficient Thermolysis Route to Monodisperse Cu2ZnSnS4 Nanocrystals with Controlled Shape and Structure

    Science.gov (United States)

    Zhang, Xiaoyan; Guo, Guobiao; Ji, Cheng; Huang, Kai; Zha, Chenyang; Wang, Yifeng; Shen, Liming; Gupta, Arunava; Bao, Ningzhong

    2014-05-01

    Monodisperse Cu2ZnSnS4 (CZTS) nanocrystals with tunable shape, crystalline phase, and composition are synthesized by efficient thermolysis of a single source precursor of mixed metal-oleate complexes in hot organic solvents with dissolved sulfur sources. Suitable tuning of the synthetic conditions and the Cu/(Zn + Sn) ratio of the precursor has enabled precise control of the crystalline phase in the form of kesterite, or a newly observed wurtzite structure. Nanocrystals with morphology in the form of spherical, rice-like, or rod-like shapes are obtained over a wide range of compositions (0.5 <= Cu/(Zn + Sn) <= 1.2). Both the final products and intermediates for each shape exhibit consistent composition and structure, indicating homogenous nucleation and growth of single-phase nanocrystals. Thin films prepared from colloidal nanocrystal suspensions display interesting shape-dependent photoresponse behavior under white light illumination from a solar simulator.

  7. Spinning the fuzzy sphere

    Energy Technology Data Exchange (ETDEWEB)

    Berenstein, David [Department of Applied Mathematics and Theoretical Physics,University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Department of Physics, University of California Santa Barbara,Santa Barbara, California 93106 (United States); Dzienkowski, Eric; Lashof-Regas, Robin [Department of Physics, University of California Santa Barbara,Santa Barbara, California 93106 (United States)

    2015-08-27

    We construct various exact analytical solutions of the SO(3) BMN matrix model that correspond to rotating fuzzy spheres and rotating fuzzy tori. These are also solutions of Yang Mills theory compactified on a sphere times time and they are also translationally invariant solutions of the N=1{sup ∗} field theory with a non-trivial charge density. The solutions we construct have a ℤ{sub N} symmetry, where N is the rank of the matrices. After an appropriate ansatz, we reduce the problem to solving a set of polynomial equations in 2N real variables. These equations have a discrete set of solutions for each value of the angular momentum. We study the phase structure of the solutions for various values of N. Also the continuum limit where N→∞, where the problem reduces to finding periodic solutions of a set of coupled differential equations. We also study the topology change transition from the sphere to the torus.

  8. Seeded growth of titania colloids with refractive index tunability and fluorophore-free luminescence.

    Science.gov (United States)

    Demirörs, Ahmet Faik; Jannasch, Anita; van Oostrum, Peter D J; Schäffer, Erik; Imhof, Arnout; van Blaaderen, Alfons

    2011-03-01

    Titania is an important material in modern materials science, chemistry, and physics because of its special catalytic, electric, and optical properties. Here, we describe a novel method to synthesize colloidal particles with a crystalline titania, anatase core and an amorphous titania-shell structure. We demonstrate seeded growth of titania onto titania particles with accurate particle size tunability. The monodispersity is improved to such an extent so that colloidal crystallization of the grown microspheres becomes feasible. Furthermore, seeded growth provides separate manipulation of the core and shell. We tuned the refractive index of the amorphous shell between 1.55 and 2.3. In addition, the particles show luminescence when trace amounts of aminopropyl-triethoxysilane are incorporated into the titania matrix and are calcined at 450 °C. Our novel colloids may be useful for optical materials and technologies such as photonic crystals and optical trapping.

  9. Au, Ag and Au:Ag colloidal nanoparticles synthesized by pulsed laser ablation as SERS substrates

    Directory of Open Access Journals (Sweden)

    M. Vinod

    2014-12-01

    Full Text Available Chemically pure colloidal suspensions of gold and silver nanoparticles were synthesized using pulsed laser ablation. The dependence of laser fluence on the surface plasmon characteristics of the nanoparticles was investigated. Au:Ag colloidal suspensions were prepared by mixing highly monodisperse Au and Ag nanocolloids. The plasmon band of these mixtures was found to be highly sensitive to Au:Ag concentration ratio and wavelength of the laser beam used in the ablation process. The Au:Ag mixture consists of almost spherical shaped nanostructures with a tendency to join with adjacent ones. The surface enhanced Raman scattering activity of the Au, Ag and Au:Ag colloidal suspensions was tested using crystal violet as probe molecules. Enhancement in Raman signal obtained with Au:Ag substrates was found to be promising and strongly depends on its plasmon characteristics.

  10. Au, Ag and Au:Ag colloidal nanoparticles synthesized by pulsed laser ablation as SERS substrates

    Institute of Scientific and Technical Information of China (English)

    M. Vinod; K.G.Gopchandran

    2014-01-01

    Chemically pure colloidal suspensions of gold and silver nanoparticles were synthesized using pulsed laser ablation. The dependence of laser fluence on the surface plasmon characteristics of the nanoparticles was investigated. Au:Ag colloidal suspensions were prepared by mixing highly monodisperse Au and Ag nanocolloids. The plasmon band of these mixtures was found to be highly sensitive to Au:Ag concentration ratio and wavelength of the laser beam used in the ablation process. The Au:Ag mixture consists of almost spherical shaped nanostructures with a tendency to join with adjacent ones. The surface enhanced Raman scattering activity of the Au, Ag and Au:Ag colloidal suspensions was tested using crystal violet as probe molecules. Enhancement in Raman signal obtained with Au:Ag substrates was found to be promising and strongly depends on its plasmon characteristics.

  11. 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.

  12. 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.

  13. Colloidal solitary waves with temperature dependent compressibility

    Science.gov (United States)

    Azmi, A.; Marchant, T. R.

    2014-05-01

    Spatial solitary waves which form in colloidal suspensions of dielectric nanoparticles are considered. The interactions, or compressibility, of the colloidal particles, is modelled using a series in the particle density, or packing fraction, where the virial, or series, coefficients depend on the type of particle interaction model. Both the theoretical hard disk and sphere repulsive models, and a model with temperature dependent compressibility, are considered. Experimental results show that particle interactions can be temperature dependent and either repulsive or attractive in nature, so we model the second virial coefficient using a physically realistic temperature power law. One- and two-dimensional semi-analytical colloidal solitary wave solutions are found. Trial functions, based on the form of the nonlinear Schrödinger equation soliton, are used, together with averaging, to develop the semi-analytical solutions. When the background packing fraction is low, the one-dimensional solitary waves have three solutions branches (with a bistable regime) while the two-dimensional solitary waves have two solution branches, with a single stable branch. The temperature dependent second virial coefficient results in changes to the solitary wave properties and the parameter space, in which multiple solutions branches occur. An excellent comparison is found between the semi-analytical and numerical solutions.

  14. Patchy polymer colloids with tunable anisotropy dimensions.

    Science.gov (United States)

    Kraft, Daniela J; Hilhorst, Jan; Heinen, Maria A P; Hoogenraad, Mathijs J; Luigjes, Bob; Kegel, Willem K

    2011-06-09

    We present the synthesis of polymer colloids with continuously tunable anisotropy dimensions: patchiness, roughness, and branching. Our method makes use of controlled fusion of multiple protrusions on highly cross-linked polymer particles produced by seeded emulsion polymerization. Carefully changing the synthesis conditions, we can tune the number of protrusions, or branching, of the obtained particles from spheres with one to three patches to raspberry-like particles with multiple protrusions. In addition to that, roughness is generated on the seed particles by adsorption of secondary nucleated particles during synthesis. The size of the roughness relative to the smooth patches can be continuously tuned by the initiator, surfactant, and styrene concentrations. Seed colloids chemically different from the protrusions induce patches of different chemical nature. The underlying generality of the synthesis procedure allows for application to a variety of seed particle sizes and materials. We demonstrate the use of differently sized polyNIPAM (poly-N-isopropylacrylamide), as well as polystyrene and magnetite filled polyNIPAM seed particles, the latter giving rise to magnetically anisotropic colloids. The high yield together with the uniform, anisotropic shape make them interesting candidates for use as smart building blocks in self-assembling systems.

  15. AlphaSphere

    OpenAIRE

    Place, A.; Lacey, L.; Mitchell, T.

    2013-01-01

    The AlphaSphere is an electronic musical instrument featuring a series of tactile, pressure sensitive touch pads arranged in a spherical form. It is designed to offer a new playing style, while allowing for the expressive real-time modulation of sound available in electronic-based music. It is also designed to be programmable, enabling the flexibility to map a series of different notational arrangements to the pad-based interface.\\ud \\ud The AlphaSphere functions as an HID, MIDI and OSC devic...

  16. 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...

  17. 胶体模板法制备三维锗光子晶体%THREE-DIMENSIONAL GERMANIUM PHOTONIC CRYSTALS PREPARED BY COLLOIDAL TEMPLATE METHOD

    Institute of Scientific and Technical Information of China (English)

    张良静; 许静; 龙永福; 谢凯

    2006-01-01

    采用胶体模板法并通过简单可控的化学填充工艺制备了三维锗光子晶体:以单分散二氧化硅小球的蛋白石结构为模板,由氯化亚锗与丙烯酸化合制备得到3-三氯锗丙酸(Cl3GeCH2CH2COOH)白色粉末,以三氯锗丙酸的乙醇溶液作为锗源先驱体,低温水解得到β-羧乙基锗倍半氧化物,在600~660℃经H2还原后形成锗,由2%HF化学浸蚀消除模板,对终产物进行X射线衍射分析.结果表明:产物为多晶锗.通过扫描电子显微镜对终产物的形貌进行观察的结果表明:包裹有空气的锗壳球有序阵列已经形成.将先驱体浓度为0.6 mol/L的溶液填入模板空隙后,壳层表面可以获得较为光滑致密的锗壳.%Three-dimensional photonic crystals (PCs) were prepared by colloidal template method through a simple controllable chemical filling technique. The synthetic opal made from monodisperse silica colloidal spheres was used as a template, and a white powder of 3-trichlorogermanium propanoic acid (Cl3 GeCH2 CH2 COOH )was synthesized by combination reaction between germanium( Ⅱ )chloride and crylic acid. The Cl3 GeCH2 CH2 COOH solution in ethanol as the germanium precursor was infiltrated into the opal template voids, which was hydrolyzed to form carboxyethyl germanium sesquioxide and reduced by H2 at600 660℃ to form germanium, and then the template was removed chemically by being etched in 2% HF solution. The X-ray diffraction result shows that the final product is the polycrystalline germanium phase. The surface morphology of the final product observed by scanning electron microscopy (SEM) shows that an ordered array composed of air spheres coated with germanium shells was formed. The SEM photographs of the shell surfaces indicate that a smooth and compact shell can be formed when the concentration of the precursor is 0.6 mol/L.

  18. Rotational dynamics of magnetic silica spheres studied by measuring the complex magnetic susceptibility

    NARCIS (Netherlands)

    Claesson, E.M.; Erne, B.H.; Philipse, A.P.

    2007-01-01

    The weak permanent magnetic dipole moment of cobalt ferrite-doped colloidal silica spheres was increased by exposure to a saturating magnetic field. The resulting change of the rotational dynamics of the magnetic microspheres in a weak alternating field was measured from low to high volume fraction

  19. Thermoplastic polyurethanes with TDI-based monodisperse hard segments

    NARCIS (Netherlands)

    De, D.; Araichimani, A.; ten Hoopen, Hermina W.M.; Gaymans, R.J.

    2009-01-01

    Polyurethanes with PTMO soft segments and toluene diisocyanate diamide as urethane segment were studied. The toluene diisocyanate diamide urethane segment was monodisperse in length. The soft segment length was changed by extending PTMO with TDI units to a soft segment length varying from 2 250 to

  20. Highly monodisperse bismuth nanoparticles and their three-dimensional superlattices.

    Science.gov (United States)

    Yarema, Maksym; Kovalenko, Maksym V; Hesser, Günter; Talapin, Dmitri V; Heiss, Wolfgang

    2010-11-01

    A simple and reproducible synthesis of highly monodisperse and ligand-protected bismuth nanoparticles (Bi NPs) is reported. The size of the single-crystalline and spherically shaped NPs is controlled between 11 and 22 nm mainly by the reaction temperature. The high uniformity of the NPs allows their self-assembly into long-range-ordered two- and three-dimensional superstructures.

  1. STUDY ON THE FORMATION MECHANISM OF MONODISPERSE PARTICLES IN THE EMULSIFIER-FREE EMULSION POLYMERIZATION OF METHYL METHACRYLATE AND BUTYL ACRYLATE

    Institute of Scientific and Technical Information of China (English)

    Hong-quan Xie; Gui-ying Liao; Yu Gao

    2003-01-01

    The formation mechanism of monodisperse polymer latex particles in the emulsifier-free emulsion polymerization of methyl methacrylate and butyl acrylate with potassium persulfate as initiator was investigated. A multi-step formation mechanism for the monodisperse polymer particles was proposed. The nucleation mechanism is considered to be the coagulation of the precursor particles by homogeneous nucleation when the primary particles reach a critical size with high surface charge density and sufficient stability. It had been proved by a special experiment that the early latex particles formed by the coagulation were stable. The primary particles grow by absorbing monomers and radicals in the polymerization system and then become colloidally unstable again due to the understandable decrease of particle surface charge density, which leads to the aggregation of the growing particles and the formation of larger latex particles therefrom. After the nucleation period,the preferential aggregation of the smaller particles in the propagation process leads to the change of the particles towards a uniform size and narrower particle size distribution. The coexistence and competition of homogeneous nucleation,coagulation, propagation and aggregation result in the increase of the polydispersity index (U = D43/D10) in the first stage,then its decrease in the later stage because of the competition of propagation and aggregation, and the gradual formation of the monodisperse particles.

  2. Oxygen plasma etching-induced crystalline lattice transformation of colloidal photonic crystals.

    Science.gov (United States)

    Ding, Tao; Wang, Fei; Song, Kai; Yang, Guoqiang; Tung, Chen-Ho

    2010-12-15

    This communication describes the transformation of a colloidal crystalline lattice that was realized via oxygen plasma etching of colloidal crystals made of SiO2@PMMA core-shell microspheres. The plasma etching of the colloidal crystals proceeded nonuniformly from the top to the bottom of the colloidal crystals. The PMMA shell was etched away by the oxygen plasma in a layer-by-layer manner, and the silica core was drawn into the pit formed by the neighboring spheres in the layer below. Consequently, the crystalline lattice was transformed while the order was maintained. Scanning electron microscopy images and reflection spectra further confirmed the change in the crystalline structures. Colloidal crystals with sc and bcc lattices can be fabricated if the ratio of the polymer shell thickness to the silica core diameter is equal to certain values. More importantly, this approach may be applicable to the fabrication of various assembly structures with different inorganic particles.

  3. The Moyal Sphere

    CERN Document Server

    Eckstein, Michał; Wulkenhaar, Raimar

    2016-01-01

    We construct a family of constant curvature metrics on the Moyal plane and compute the Gauss-Bonnet term for each of them. They arise from the conformal rescaling of the metric in the orthonormal frame approach. We find a particular solution, which corresponds to the Fubini-Study metric and which equips the Moyal algebra with the geometry of a noncommutative sphere.

  4. The Moyal sphere

    Science.gov (United States)

    Eckstein, Michał; Sitarz, Andrzej; Wulkenhaar, Raimar

    2016-11-01

    We construct a family of constant curvature metrics on the Moyal plane and compute the Gauss-Bonnet term for each of them. They arise from the conformal rescaling of the metric in the orthonormal frame approach. We find a particular solution, which corresponds to the Fubini-Study metric and which equips the Moyal algebra with the geometry of a noncommutative sphere.

  5. Inhomogeneous model colloid-polymer mixtures: adsorption at a hard wall.

    Science.gov (United States)

    Brader, J M; Dijkstra, M; Evans, R

    2001-04-01

    We study the equilibrium properties of inhomogeneous model colloid-polymer mixtures. By integrating out the degrees of freedom of the ideal polymer coils, we derive a formal expression for the effective one-component Hamiltonian of the (hard sphere) colloids that is valid for arbitrary external potentials acting on both the colloids and the polymers. We show how one can recover information about the distribution of polymer in the mixture given knowledge of the colloid correlation functions calculated using the effective one-component Hamiltonian. This result is then used to furnish the connection between the free-volume and perturbation theory approaches to determining the bulk phase equilibria. For the special case of a planar hard wall the effective Hamiltonian takes an explicit form, consisting of zero-, one-, and two-body, but no higher-body, contributions provided the size ratio q=sigma(p)/sigma(c)sigma(c) and sigma(p) denote the diameters of colloid and polymer respectively. We employ a simple density functional theory to calculate colloid density profiles from this effective Hamiltonian for q=0.1. The resulting profiles are found to agree well with those from Monte Carlo simulations for the same Hamiltonian. Adding very small amounts of polymer gives rise to strong depletion effects at the hard wall which lead to pronounced enhancement of the colloid density profile (close to the wall) over what is found for hard spheres at a hard wall.

  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. Preparation of 3D Colloidal Crystal Film and Gold-Infiltrated Silica Artificial Opals%3D胶状晶体膜及其渗透金的氧化硅人工蛋白石的制备

    Institute of Scientific and Technical Information of China (English)

    李文江; 谢飞

    2007-01-01

    A free-standing 3D colloidal crystal film (opal) was fabricated at a water-air interface using purified monodispersed SiO2 colloids. The gold/silica opal was obtained through the infiltration of gold nanoparticles by electroplating. The transmission and reflection spectra of the gold/silica composite opal show a red shift with increasing electroplating time.SEM images show that gold nanoparticles can be directly deposited on the surface of silica spheres in the opaline structure. Gold/silica composite opal film could provide a simple way to tune opal properties through controlling the amount of gold in the silica opal.%用纯的单分散氧化硅胶体微球作为基质,在水-空气界面构筑无载体三维有序胶质晶体膜.该高度有序三维周期性结构具有明显的光学衍射现象.利用电沉积的方法将纳米金渗透到这种人工蛋白石的空隙中,构成gold/silica复合蛋白石材料.详细研究了该复合蛋白石的透射光谱和反射光谱,用扫描电镜观察了复合蛋白石结构的形貌特征,并对渗透金后蛋白石的光谱移动进行了分析.

  8. Synthesis of highly monodisperse Ge crystals in a capacitively coupled flow through reactor for photovoltaic applications

    Science.gov (United States)

    Gresback, Ryan; Kortshagen, Uwe

    2006-10-01

    Germanium nanocrystals are interesting candidates for quantum dot-based solar cells. While the band gap of bulk Ge is ˜0.7 eV, the energy gap can be increased due to quantum confinement to ˜ 2eV for Ge particles of ˜3 nm in size. With a single material, Ge nanocrystals of sizes from 3 -15 nm would thus allow to span the entire range of band gaps that is of interest for photovoltaic devices. Moreover, compared to many other quantum dot materials that are currently studied for photovoltaic applications, Ge is perceived as non-toxic and environmentally benign. Ge nanocrystals are synthesized in a tubular, capacitively coupled flow through reactor. Germanium tetrachloride is used as a precursor. It is introduced into the plasma by a flow of argon and hydrogen. At typical pressures of 2 Torr and 40 W of RF power at 13.56 MHz, Ge crystals are generated and reside in the plasma for several tens of milliseconds. The size of the nanocrystals can be controlled in a range from 3-20 nm through the residence time. Particles are highly monodisperse. Organically passivated Ge nanocrystals self-assemble into monolayers when cast from colloidal solutions.

  9. Small-angle scattering from precipitates: Analysis by use of a polydisperse hard-sphere model

    DEFF Research Database (Denmark)

    Pedersen, J.S.

    1993-01-01

    A general polydisperse hard-sphere model for analyzing small-angle-scattering data from spherical precipitates in alloys is presented. In the model the size distribution is chosen as a Weibull density distribution and the hard-sphere interaction radius is taken as being proportional to the radius...... very good fits to the experimental data and the results are in agreement with a Li content of 25% in the precipitates. The concentration of Li in the matrix is also in good agreement with the phase diagram of Al-Li found in the literature. Results from the application of a monodisperse hard-sphere...... of the precipitates. The Weibull distribution is monomodal, and depending on the parameters describing the distribution, it can skew to either side. Small-angle x-ray- and neutron-scattering data, taken from the literature, from spherical delta' precipitates in Al-Li alloys have been analyzed with the model. It gives...

  10. ORGANIZATION IN CONTEMPORARY PUBLIC SPHERE

    Directory of Open Access Journals (Sweden)

    Rosemarie HAINES

    2013-12-01

    Full Text Available The critical analysis of Habermas’ Public Sphere Theory and the comparative undertaking to the current day enables us to assert that in contemporary society, public sphere is no longer a political public sphere, this dimension being completed by a societal dimension, the public sphere has extended and now we can talk about partial public spheres in an ever more commercial environment. The new rebuilding and communication technologies create a new type of public character: the visible sphere – non-located, non-dialogical and open. Information and communication are more and more involved in the restructuring of capitalism on an international scale and the reorganization of leadership and management systems. The reevaluation of the public sphere, public opinion, communication allows us to define public sphere according to the profound mutations from today’s democratic societies.

  11. Synthesis of PS/Ag nanocomposite spheres with catalytic and antibacterial activities.

    Science.gov (United States)

    Deng, Ziwei; Zhu, Haibao; Peng, Bo; Chen, Hong; Sun, Yuanfang; Gang, Xiaodong; Jin, Pujun; Wang, Juanli

    2012-10-24

    This paper describes a simple, mild, and environmentally friendly approach to synthesize polystyrene/Ag (PS/Ag) nanocomposite spheres, which makes use of both reducing and stabilizing functions of polyvinylpyrrolidone (PVP) in aqueous media. In this approach, monodisperse polystyrene (PS) spheres, which are used as templates for the synthesis of core-shell nanocomposite spheres, are sulfonated first. Then, [Ag(NH(3))(2)](+) ions are adsorbed onto the surface of the PS template spheres via electrostatic attraction between -SO(3)H groups (grafted on the surface of the PS template spheres) and [Ag(NH(3))(2)](+) ions. [Ag(NH(3))(2)](+) ions are then reduced by and simultaneously protected by PVP. In this way, the PS/Ag nanocomposite spheres in aqueous media are obtained through a so-called one-pot method. Neither additional reducing agents nor toxic organic solvents are utilized during the synthesis process. Furthermore, the coverage degree and the particle size of Ag nanoparticles on PS/Ag nanocomposite spheres is easily tuned by changing the concentration of [Ag(NH(3))(2)](+) ions in aqueous media. Moreover, these PS/Ag nanocomposite spheres can be used as catalyst for the reduction of organic dyes and as antibacterial agents against Salmonella and Escherichia coli. In the present study, these PS/Ag nanocomposite spheres exhibit excellent catalytic properties (both in efficiency and recyclability) for the reduction of organic dyes, and the preliminary antibacterial assays indicate that these PS/Ag nanocomposite spheres also possess extraordinary antibacterial abilities against Salmonella and Escherichia coli.

  12. Entropical Colloidal Interaction in Rod-like Molecules Solution

    Science.gov (United States)

    Hohlfeld, Evan B.; Lin, Keng-Hui; Zeri, Ana Carolina; Crocker, John C.; Yodh, Arjun G.

    2001-03-01

    We report direct measurements of the functional form of the depletion interaction between two colloidal spheres in a rod-like molecule suspension the line-scanned optical tweezer. The rod like moleculses are bacteriaphage fd with length (L) 880 nm and diameter(D) 6.5 nm and TMV with L 300 nm and D 200 nm. We probed different ratios of sphere radius R and rod length L and compared with theoretical models of Yaman^. The experimental data agrees with the model with slight discrepancy due to the flexibility of rod molecules. At high salt concentration, we also observed the steric repulsion due rod molecule stuck on the spheres. We gratefully acknowledge support from the NSF (DMR-9623441) and MRSEC (DMR-9632598). K. Yaman, C. Jeppesen and C.M. Marques, Europhys. Lett., 42, 221 (1998).

  13. Neural tissue-spheres

    DEFF Research Database (Denmark)

    Andersen, Rikke K; Johansen, Mathias; Blaabjerg, Morten

    2007-01-01

    maintained their neurogenic potential throughout 77 days of propagation, while the ability of anterior NTS to generate neurons severely declined from day 40. The present procedure describes isolation and long-term expansion of forebrain SVZ tissue with potential preservation of the endogenous cellular......By combining new and established protocols we have developed a procedure for isolation and propagation of neural precursor cells from the forebrain subventricular zone (SVZ) of newborn rats. Small tissue blocks of the SVZ were dissected and propagated en bloc as free-floating neural tissue......-spheres (NTS) in EGF and FGF2 containing medium. The spheres were cut into quarters when passaged every 10-15th day, avoiding mechanical or enzymatic dissociation in order to minimize cellular trauma and preserve intercellular contacts. For analysis of regional differences within the forebrain SVZ, NTS were...

  14. Laser Synthesis and Processing of Colloids: Fundamentals and Applications.

    Science.gov (United States)

    Zhang, Dongshi; Gökce, Bilal; Barcikowski, Stephan

    2017-03-08

    Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials, thereby enabling the fabrication of bioconjugates and heterogeneous catalysts. Accurate size control of LSPC-synthesized materials ranging from quantum dots to submicrometer spheres and recent upscaling advancement toward the multiple-gram scale are helpful for extending the applicability of LSPC-synthesized nanomaterials to various fields. By discussing key reports on both the fundamentals and the applications related to laser ablation, fragmentation, and melting in liquids, this Article presents a timely and critical review of this emerging topic.

  15. Absolute multilateration between spheres

    Science.gov (United States)

    Muelaner, Jody; Wadsworth, William; Azini, Maria; Mullineux, Glen; Hughes, Ben; Reichold, Armin

    2017-04-01

    Environmental effects typically limit the accuracy of large scale coordinate measurements in applications such as aircraft production and particle accelerator alignment. This paper presents an initial design for a novel measurement technique with analysis and simulation showing that that it could overcome the environmental limitations to provide a step change in large scale coordinate measurement accuracy. Referred to as absolute multilateration between spheres (AMS), it involves using absolute distance interferometry to directly measure the distances between pairs of plain steel spheres. A large portion of each sphere remains accessible as a reference datum, while the laser path can be shielded from environmental disturbances. As a single scale bar this can provide accurate scale information to be used for instrument verification or network measurement scaling. Since spheres can be simultaneously measured from multiple directions, it also allows highly accurate multilateration-based coordinate measurements to act as a large scale datum structure for localized measurements, or to be integrated within assembly tooling, coordinate measurement machines or robotic machinery. Analysis and simulation show that AMS can be self-aligned to achieve a theoretical combined standard uncertainty for the independent uncertainties of an individual 1 m scale bar of approximately 0.49 µm. It is also shown that combined with a 1 µm m‑1 standard uncertainty in the central reference system this could result in coordinate standard uncertainty magnitudes of 42 µm over a slender 1 m by 20 m network. This would be a sufficient step change in accuracy to enable next generation aerospace structures with natural laminar flow and part-to-part interchangeability.

  16. VMware vSphere Design

    CERN Document Server

    Guthrie, Forbes; Saidel-Keesing, Maish

    2011-01-01

    The only book focused on designing VMware vSphere implementations.VMware vSphere is the most widely deployed virtualization platform today. Considered the most robust and sophisticated hypervisor product, vSphere is the de facto standard for businesses, both large and small. This book is the only one of its kind to concisely explain how to execute a successful vSphere architecture, tailored to meet your company's needs. Expert authors share with you the factors that shape the design of a vSphere implementation. Learn how to make the right design decisions for your environment.Explores the late

  17. Effects of shear and walls on the diffusion of colloids in microchannels

    NARCIS (Netherlands)

    Ghosh, S.; Mugele, F.; Duits, M.H.G.

    2015-01-01

    Colloidal suspensions flowing through microchannels were studied for the effects of both the shear flow and the proximity of walls on the particles' self-diffusion. Use of hydrostatic pressure to pump micron-sized silica spheres dispersed in water-glycerol mixture through poly(dimethylsiloxane) chan

  18. Sedimentation equilibria of ferrofluids: II. Experimental osmotic equations of state of magnetite colloids

    NARCIS (Netherlands)

    Luigjes, B.; Thies-Weesie, D.M.E.; Erné, B.H.; Philipse, A.P.

    2012-01-01

    The first experimental osmotic equation of state is reported for well-defined magnetic colloids that interact via a dipolar hard-sphere potential. The osmotic pressures are determined from the sedimentation equilibrium concentration profiles in ultrathin capillaries using a low-velocity analytical c

  19. Model independent determination of colloidal silica size distributions via analytical ultracentrifugation

    NARCIS (Netherlands)

    Planken, K.L.; Kuipers, B.W.M.; Philipse, A.P.

    2008-01-01

    We report a method to determine the particle size distribution of small colloidal silica spheres via analytical ultracentrifugation and show that the average particle size, variance, standard deviation, and relative polydispersity can be obtained from a single sedimentation velocity (SV) analytical

  20. Colloidal dispersions of repulsive nanoparticles : tunable effective interactions, phase behaviour and anisotropy

    NARCIS (Netherlands)

    Everts, J.C.

    2016-01-01

    We investigated various aspects of colloidal dispersions. In this study we not only emphasized the tunability of the particle properties (rods versus spheres, charging properties of the particle surface), but also the properties of the medium in which they reside (oil and/or water). These properties

  1. Effects of shear and walls on the diffusion of colloids in microchannels

    NARCIS (Netherlands)

    Ghosh, Somnath; Mugele, Friedrich Gunther; Duits, Michael H.G.

    2015-01-01

    Colloidal suspensions flowing through microchannels were studied for the effects of both the shear flow and the proximity of walls on the particles' self-diffusion. Use of hydrostatic pressure to pump micron-sized silica spheres dispersed in water-glycerol mixture through poly(dimethylsiloxane) chan

  2. A co-flow-focusing monodisperse microbubble generator

    KAUST Repository

    Zhang, Jiaming

    2014-02-14

    We use a simple and inexpensive microfluidic device, which is based on microscope glass slides and two tapered glass capillaries, to produce monodisperse microbubbles. The innermost capillary used for transporting the gas is inserted into the second capillary, with its 2 μm sharp tip aligned with the center of the converging-diverging throat of the second capillary. This configuration provides a small and smooth gas flow rate, and a high velocity gradient at the tube outlet. Highly monodisperse microbubbles with diameters ranging from 3.5 to 60 microns have been successfully produced at a rate of up to 40 kHz. A simple scaling law, which is based on the capillary number and liquid-to-gas flow rate ratio, successfully predicts the bubble size. © 2014 IOP Publishing Ltd.

  3. Synthesis and antimicrobial activity of monodisperse copper nanoparticles.

    Science.gov (United States)

    Kruk, Tomasz; Szczepanowicz, Krzysztof; Stefańska, Joanna; Socha, Robert P; Warszyński, Piotr

    2015-04-01

    Metallic monodisperse copper nanoparticles at a relatively high concentration (300 ppm CuNPs) have been synthesized by the reduction of copper salt with hydrazine in the aqueous SDS solution. The average particles size and the distribution size were characterized by Dynamic Light Scattering (DLS), Nanosight-Nanoparticle Tracking Analysis (NTA). The morphology and structure of nanoparticles were investigated using Scanning Electron Microscopy (SEM). The chemical composition of the copper nanoparticles was determined by X-ray Photoelectron Spectroscopy (XPS). Monodisperse copper nanoparticles with average diameter 50 nm were received. UV/vis absorption spectra confirmed the formation of the nanoparticles with the characteristic peak 550 nm. The antimicrobial studies showed that the copper nanoparticles had high activity against Gram-positive bacteria, standard and clinical strains, including methicillin-resistant Staphylococcus aureus, comparable to silver nanoparticles and some antibiotics. They also exhibited antifungal activity against Candida species. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Synthesis of Monodisperse Iron Oxide Nanoparticles without Surfactants

    Directory of Open Access Journals (Sweden)

    Xiao-Chen Yang

    2014-01-01

    Full Text Available Monodisperse iron oxide nanoparticles could be successfully synthesized with two kinds of precipitants through a precipitation method. As-prepared nanoparticles in the size around 10 nm with regular spherical-like shape were achieved by adjusting pH values. NaOH and NH3·H2O were used as two precipitants for comparison. The average size of nanoparticles with NH3·H2O precipitant got smaller and represented better dispersibility, while nanoparticles with NaOH precipitant represented better magnetic property. This work provided a simple method without using any organic solvents, organic metal salts, or surfactants which could easily obtain monodisperse nanoparticles with tunable morphology.

  5. Preparation and Characterization of Monodisperse Nickel Nanoparticles by Polyol Process

    Institute of Scientific and Technical Information of China (English)

    LI Peng; GUAN Jianguo; ZHANG Qingjie; ZHAO Wenyu

    2005-01-01

    Polymer-protected monodisperse nickel nanoparticles were synthesized by a modified polyol reduction method in the presence of poly ( N-vinyl- 2-pyrrolidone ). These nanoparticles were characterized by transmission electron microscopy (TEM), X- ray diffraction ( XRD ), selected area electron diffraction ( SAED ), as well as vibrating sample magnetometer (VSM). The experimental results show that the addition of PVP and the concentration of NaOH have strong influences on the size, agglomeration and uniformity of nanoparticles. In the presence of PVP and NaOH with low concentrations, monodisperse nickel nanoparticles with average diameters about 42 nm were obtained and characterized to be pure nickel crystalline with fcc structure. Secondary structures such as clusters, loops, and strings resulted from magnetic interactions between particles were observed. The chemical interaction between the PVP and nickel nanoparticles was found by FTIR. The saturation magnetization ( Ms ), remanent magnetization (Mr) and coercivity ( Hc ) of these nickel nanoparticles are lower than those of bulk nickel.

  6. 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.

  7. Polydopamine spheres as active templates for convenient synthesis of various nanostructures.

    Science.gov (United States)

    Yan, Jian; Yang, Liping; Lin, Meng-Fang; Ma, Jan; Lu, Xuehong; Lee, Pooi See

    2013-02-25

    In this work, monodisperse polydopamine (PDA) spheres with tunable diameters have been synthesized through a facile and low cost method using a deionized water and alcohol mixed solvent. The PDA spheres possess surface functional groups (-OH, -NH(2)), exhibiting an extraordinary versatile active nature. It is demonstrated that the PDA spheres could serve as an active template for the convenient synthesis of various nanostructures, e.g., MnO(2) hollow spheres or PDA/Fe(3)O(4) and PDA/Ag core/shell nanostructures. No surface modification or special treatment is required for the synthesis of these nanostructures, which makes the fabrication process simple and very convenient. The novel application of PDA/Fe(3)O(4) spheres as fillers in nanocomposites for high-performance capacitors is demonstrated, indicating a promising practicality. The PDA spheres provide a new general platform not only for the facile assembly of nanostructures but also a green synthetic template for practical applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Hard sphere crystal nucleation and growth near large spherical impurities

    Science.gov (United States)

    de Villeneuve, V. W. A.; Verboekend, D.; Dullens, R. P. A.; Aarts, D. G. A. L.; Kegel, W. K.; Lekkerkerker, H. N. W.

    2005-11-01

    We report how large spherical impurities affect the nucleation and growth of hard sphere colloidal crystals. Both the impurities and the colloids are fluorescently labelled polymethylmetacrylate particles and are dispersed in an optically and density matching solvent mixture. Crystal growth, initiated either at the impurity surface, or at the sample bottom, was studied by imaging sequences of two-dimensional xy-slices in the plane of the impurity's centre of mass with a laser scanning confocal microscope. At least two factors determine whether a large impurity can function as a seed for heterogeneous nucleation: timescales and impurity curvature. The curvature needs to be sufficiently low for crystal nuclei to form on the impurity surface. If bulk crystal growth has already approached the impurity, bulk growth is dominant over growth of crystallites on the impurity surface. Such surface crystallites eventually reorient to adapt to the overall bulk crystal symmetry.

  9. Monodispersive CoPt Nanoparticles Synthesized Using Chemical Reduction Method

    Institute of Scientific and Technical Information of China (English)

    SHEN Cheng-Min; HUI Chao; YANG Tian-Zhong; XIAO Cong-Wen; CHEN Shu-Tang; DING Hao; GAO Hong-Jun

    2008-01-01

    @@ Monodispersive CoPt nanoparticles in sizes of about 2.2 nm are synthesized by superhydride reduction of CoCl2 and PtCl2 in diphenyl ether. The as-prepared nanoparticles show a chemically disordered A1 structure and are superparamagnetic. Thermal annealing transforms the A1 structure into chemically ordered L1o structure and the particles are ferromagnetic at room temperature.

  10. Monodisperse magnesium hydride nanoparticles uniformly self-assembled on graphene.

    Science.gov (United States)

    Xia, Guanglin; Tan, Yingbin; Chen, Xiaowei; Sun, Dalin; Guo, Zaiping; Liu, Huakun; Ouyang, Liuzhang; Zhu, Min; Yu, Xuebin

    2015-10-21

    Monodisperse MgH2 nanoparticles with homogeneous distribution and a high loading percent are developed through hydrogenation-induced self-assembly under the structure-directing role of graphene. Graphene acts not only as a structural support, but also as a space barrier to prevent the growth of MgH2 nanoparticles and as a thermally conductive pathway, leading to outstanding performance.

  11. Facile Synthesis of Monodisperse CdS Nanocrystals via Microreaction

    Directory of Open Access Journals (Sweden)

    Zhou Xinggui

    2009-01-01

    Full Text Available Abstract CdS-based nanocrystals (NCs have attracted extensive interest due to their potential application as key luminescent materials for blue and white LEDs. In this research, the continuous synthesis of monodisperse CdS NCs was demonstrated utilizing a capillary microreactor. The enhanced heat and mass transfer in the microreactor was useful to reduce the reaction temperature and residence time to synthesize monodisperse CdS NCs. The superior stability of the microreactor and its continuous operation allowed the investigation of synthesis parameters with high efficiency. Reaction temperature was found to be a key parameter for balancing the reactivity of CdS precursors, while residence time was shown to be an important factor that governs the size and size distribution of the CdS NCs. Furthermore, variation of OA concentration was demonstrated to be a facile tuning mechanism for controlling the size of the CdS NCs. The variation of the volume percentage of OA from 10.5 to 51.2% and the variation of the residence time from 17 to 136 s facilitated the synthesis of monodisperse CdS NCs in the size range of 3.0–5.4 nm, and the NCs produced photoluminescent emissions in the range of 391–463 nm.

  12. Self-Assembly of Ternary Particles for Tough Colloidal Crystals with Vivid Structure Colors

    Directory of Open Access Journals (Sweden)

    Binfu Bao

    2013-01-01

    Full Text Available Self-assembly of colloidal spheres is the most frequently used method for structural colors, but the chroma of the structural colors is usually so low that people cannot observe it under natural conditions. This paper presents a facile method for fabrications of vivid structural colors by doping carbon black into the self-assembly of colloidal polymer spheres and nanosilica particles. This approach can generate very gorgeous structural colors which can be very easily seen under natural conditions. The fabrication conditions for the self-assembly of composite dispersions of polymer/silica/carbon black were optimized to obtain colloidal crystals with vivid colors. Thus, robust mechanical properties, large-scale, and brilliant structural colors can guarantee the obtained crystal films to find practical applications, which are demonstrated by the fact that the successful applications of structural colors beautify the original simple and tedious surface of bamboo strand board (BSB.

  13. Fabrication of Colloidal Photonic Crystals with Heterostructure by Spin-Coating Method

    Institute of Scientific and Technical Information of China (English)

    WANG Ai-Jun; CHEN Sheng-Li; DONG Peng; CAI Xiao-Gang; ZHOU Qian; YUAN Gui-Mei; HU Chun-Tian; ZANG Dao-Zhong

    2009-01-01

    Colloidal photonic crystal heterostructures, composed of two opaline photonic crystal films of silica spheres with different diameters, are fabricated by a two-step spin-coating method. Scanning electron microscopy (SEM) and UV-vis speetrophotometer are used to characterize the heterostructures. The SEM images show good ordering of the two-layer colloidal crystals constituting the heterostructures. The transmission spectra measured from the (111) plane in the heterostructure show that the composite colloidal photonic crystals have double photonic stop bands. Furthermore, when the sizes of the silica spheres used for fabricating the composite photonic crystal are slightly different, the transmission spectrum shows that the composite photonic crystals have more extended bandgap than that of the individual photonic crystals due to partial overlapping of its two photonie stop bands.

  14. 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...

  15. Observation of Single Colloidal Platinum Nanocrystal Growth Trajectories

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Haimei; Smith, Rachel; Jun, Young-wook; Kisielowski, Christian; Dahmen, Ulrich; Alivisatos, A. Paul

    2009-02-09

    It is conventionally assumed that the growth of monodisperse colloidal nanocrystals requires a temporally discrete nucleation followed by monomer attachment onto the existing nuclei. However, recent studies have reported violations of this classical growth model, and have suggested that inter-particle interactions are also involved during the growth. Mechanisms of nanocrystal growth still remain controversial. Using in situ transmission electron microscopy, we show that platinum nanocrystals can grow either by monomer attachment from solution onto the existing particles or by coalescence between the particles. Surprisingly, an initially broad size distribution of the nanocrystals can spontaneously narrow. We suggest that nanocrystals take different pathways of growth based on their size- and morphology-dependent internal energies. These observations are expected to be highly relevant for other nanocrystal systems.

  16. Phase diagram of highly asymmetric binary hard-sphere mixtures.

    Science.gov (United States)

    Dijkstra, M; van Roij, R; Evans, R

    1999-05-01

    We study the phase behavior and structure of highly asymmetric binary hard-sphere mixtures. By first integrating out the degrees of freedom of the small spheres in the partition function we derive a formal expression for the effective Hamiltonian of the large spheres. Then using an explicit pairwise (depletion) potential approximation to this effective Hamiltonian in computer simulations, we determine fluid-solid coexistence for size ratios q=0.033, 0.05, 0.1, 0.2, and 1.0. The resulting two-phase region becomes very broad in packing fractions of the large spheres as q becomes very small. We find a stable, isostructural solid-solid transition for q0 the phase diagram mimics that of the sticky-sphere system. As expected, the radial distribution function g(r) and the structure factor S(k) of the effective one-component system show no sharp signature of the onset of the freezing transition and we find that at most points on the fluid-solid boundary the value of S(k) at its first peak is much lower than the value given by the Hansen-Verlet freezing criterion. Direct simulations of the true binary mixture of hard spheres were performed for q > or =0.05 in order to test the predictions from the effective Hamiltonian. For those packing fractions of the small spheres where direct simulations are possible, we find remarkably good agreement between the phase boundaries calculated from the two approaches-even up to the symmetric limit q=1 and for very high packings of the large spheres, where the solid-solid transition occurs. In both limits one might expect that an approximation which neglects higher-body terms should fail, but our results support the notion that the main features of the phase equilibria of asymmetric binary hard-sphere mixtures are accounted for by the effective pairwise depletion potential description. We also compare our results with those of other theoretical treatments and experiments on colloidal hard-sphere mixtures.

  17. Tow-Dimensional Micro-grating Formed by Polystyrene Spheres

    Institute of Scientific and Technical Information of China (English)

    张琦; 倪培根; 孟庆波; 程丙英; 张道中

    2003-01-01

    We report a simple method to make two-dimensional plane gratings that can be used as splitters. In the selfassembly process, the colloidal spheres can form single layer square or triangular lattice on a flat surface and in our experiments the triangular lattice is a more common structure. As an incident beam passes through the triangular lattice, it can be split into seven sub-beams, among which six beams have the same density and scattering angle. This grating is not sensitive to the polarization direction of the incident light.

  18. Hydrodynamic force between a sphere and a soft, elastic surface.

    Science.gov (United States)

    Kaveh, Farzaneh; Ally, Javed; Kappl, Michael; Butt, Hans-Jürgen

    2014-10-07

    The hydrodynamic drainage force between a spherical silica particle and a soft, elastic polydimethylsiloxane surface was measured using the colloidal probe technique. The experimental force curves were compared to finite element simulations and an analytical model. The hydrodynamic repulsion decreased when the particle approached the soft surface as compared to a hard substrate. In contrast, when the particle was pulled away from the surface again, the attractive hydrodynamic force was increased. The hydrodynamic attraction increased because the effective area of the narrow gap between sphere and the plane on soft surfaces is larger than on rigid ones.

  19. Seeking New Model Geometry to Predict the Fate and Transport of Colloids in Porous Media

    Science.gov (United States)

    Ma, H.; Johnson, W. P.

    2008-12-01

    Classic colloidal filtration theory (CFT) employed particle tracking approaches in Happel sphere-in-cell model to predict transport and deposition rates of colloids in clean bed porous media. It works well when an energy barrier to deposition is absent, but fails when repulsion exists between the colloid and the collecting surface. Past efforts in modifying CFT, e.g. including a sticking coefficient to account for effect of colloid-collector repulsion on deposition, have not yielded consistently successful predictions. Recent advances in understanding colloidal retention in porous media in the presence of an energy barrier demonstrated two important deposition mechanisms: 1) wedging/straining at grain-to-grain contacts; and 2) retention at secondary energy minima with sufficiently low flow (e.g. flow stagnation zones). These mechanisms are not considered in CFT, partly because the sphere-in-cell model on which CFT is based lacks the necessary pore geometry feature (e.g. grain-to-grain contacts). Here we explore new model geometries that utilize the fluid envelope feature from CFT, but also incorporate grain-to-grain contacts. This presentation describes the testing of these new model geometries in predicting colloidal deposition in the absence of an energy barrier, and then extends to conditions when repulsive energy barriers to deposition are present.

  20. Active microrheology in a colloidal glass

    Science.gov (United States)

    Gruber, M.; Abade, G. C.; Puertas, A. M.; Fuchs, M.

    2016-10-01

    We study the dynamics of a probe particle driven by a constant force through a colloidal glass of hard spheres. This nonequilibrium and anisotropic problem is investigated using a new implementation of the mode-coupling approximation with multiple relaxation channels and Langevin dynamics simulations. A force threshold is found, below which the probe remains localized, while above it the probe acquires a finite velocity. We focus on the localized regime, comparing theory and simulations concerning the dynamics in the length scale of the cage and the properties of the transition to the delocalized regime, such as the critical power-law decay of the probe correlation function. Probe van Hove functions predicted by the theory show exponential tails reminiscent of an intermittent dynamics of the probe. This scenario is microscopically supported by simulations.

  1. 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.

  2. 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.

  3. 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.

  4. Binary colloidal crystals

    NARCIS (Netherlands)

    Christova-Zdravkova, C.G.

    2005-01-01

    Binary crystals are crystals composed of two types of particles having different properties like size, mass density, charge etc. In this thesis several new approaches to make binary crystals of colloidal particles that differ in size, material and charge are reported We found a variety of crystal st

  5. Electrodynamics of colloids.

    NARCIS (Netherlands)

    Minor, M.

    1998-01-01

    The goal of the present study is to deepen the insight into the non-equilibrium properties of the electric double layer of colloidal systems. Of basic interest are the ionic mobilities in the different regions of the electric double layer as well as the potential at the plane of shear, i.e., the ele

  6. Fundamental measure theory for hard-sphere mixtures: a review.

    Science.gov (United States)

    Roth, Roland

    2010-02-17

    Hard-sphere systems are one of the fundamental model systems of statistical physics and represent an important reference system for molecular or colloidal systems with soft repulsive or attractive interactions in addition to hard-core repulsion at short distances. Density functional theory for classical systems, as one of the core theoretical approaches of statistical physics of fluids and solids, has to be able to treat such an important system successfully and accurately. Fundamental measure theory is up to date the most successful and most accurate density functional theory for hard-sphere mixtures. Since its introduction fundamental measure theory has been applied to many problems, tested against computer simulations, and further developed in many respects. The literature on fundamental measure theory is already large and is growing fast. This review aims to provide a starting point for readers new to fundamental measure theory and an overview of important developments.

  7. Diffusion and structure of a quasi-one-dimensional hard-sphere fluid

    Science.gov (United States)

    Lin, Binhua; Lee, Ji Hwan; Cui, Bianxiao

    2001-03-01

    We report the results of an experimental study of a quasi-one-dimensional hard-sphere fluid. The system consists of uncharged Si colloidal spheres confined in long, uncorrelated 1D-channels whose narrow width forbids mutual passage of spheres along the channel. By tracking the trajectories of the spheres using digital video microscopy, we studied the diffusion and structure of the system as a function of the density of the fluid. Our results show that the behavior of the spheres in self-diffusion is changed gradually from Fickian to non-Fickian near the onset of the collision between the spheres, indicating the correlation between the collision of the hard-spheres and the change in diffusion mechanism. At high density, the self-part of the van Hove function of the system is no longer a Gaussian distribution but a Poisson distribution which can be interpreted using a hydrodynamic analysis for effective wall-drag effect. The pair distribution function of the system can be explained by an analytical expression for a 1D hard-sphere fluid [1]. [1] Y. Rosenfeld, M. Schmidt, H. Lowen and P. Tarazona, Phys. Rev. E 55, 4245 (1997).

  8. Ion size effect on colloidal forces within the primitive model

    Directory of Open Access Journals (Sweden)

    J.Wu

    2005-01-01

    Full Text Available The effect of ion size on the mean force between a pair of isolated charged particles in an electrolyte solution is investigated using Monte Carlo simulations within the framework of the primitive model where both colloidal particles and small ions are represented by charged hard spheres and the solvent is treated as a dielectric continuum. It is found that the short-ranged attraction between like-charged macroions diminishes as the diameter of the intermediating divalent counterions and coions increases and the maximum attractive force is approximately a linear function of the counterion diameter. This size effect contradicts the prediction of the Asakura-Oosawa theory suggesting that an increase in the excluded volume of small ions would lead to a stronger depletion between colloidal particles. Interestingly, the simulation results indicate that both the hard-sphere collision and the electrostatic contributions to the mean force are insensitive to the size disparity of colloidal particles with the same average diameter.

  9. Phase diagram of colloid-rod system

    Science.gov (United States)

    Lai, S. K.; Xiao, Xuhui

    2010-01-01

    The semigrand ensemble theory [H. N. W. Lekkerkerker, W. C. K. Poon, P. N. Pusey, A. Stroobants, and P. B. Warren, Europhys. Lett. 20, 559 (1992)] in conjunction with the fundamental measure density functional theory [V. B. Warshavsky and X. Song, Phys. Rev. E 69, 061113 (2004)] are used to construct the Helmholtz free energy densities of a mixture of uncharged colloidal hard spheres and colloidal rods in its solid and liquid phases. Given these free energy density functions, we apply the free energy density minimization method [G. F. Wang and S. K. Lai, Phys. Rev. E 70, 051402 (2004)] to crosshatch the system's regions of phases in coexistence. The calculated results show that the triangular area bounded by gas-liquid, gas-solid, and liquid-solid coexisting two phases which has been called the coexistence region of gas-liquid-solid corresponds in fact to sets of two phases in coexistence. The phase boundaries which define our calculated coexistence domains compare very well with previous theoretical calculations. The relevance of the phase-diagram domains to three phases in coexistence will be discussed.

  10. Old relief printing applied to the current preparation of multi-color and high resolution colloidal photonic crystal patterns.

    Science.gov (United States)

    Yang, Dongpeng; Ye, Siyun; Ge, Jianping

    2015-12-11

    Monodisperse SiO2 colloids are assembled into colloidal crystals in the mixture of monomer and solvent, which is transformed into a mechanochromic photonic crystal paper by polymerization. Following the relief printing strategy, the printing plates are pressed onto the paper to generate letters or images due to the contrast of structural color between the deformed and the undeformed paper, and the images can be permanently retained through UV curing. The wide tunable range of structural color for the current paper under deformation helps to realize multi-color printing. The localized deformation among or even inside the colloidal microcrystals renders the paper with a precise mechanochromic response to the printing plates and leads to the production of high resolution photonic crystal patterns.

  11. Thermodynamic and hydrodynamic interaction in concentrated microgel suspensions: Hard or soft sphere behavior?

    Science.gov (United States)

    Eckert, Thomas; Richtering, Walter

    2008-09-28

    The colloidal phase behavior, structure factors, short-time collective diffusion coefficients, and hydrodynamic interactions of concentrated poly(N-isopropylacryamide) (PNiPAM) microgels in dimethylformamide suspensions were measured with simultaneous static and dynamic three-dimensional cross-correlated light scattering. The data are interpreted through comparison with hard sphere theory. The fluid-crystal transition and the static structure factors can be described consistently by the hard sphere approximation. On the other hand, collective diffusion and hydrodynamic interaction cannot be described satisfactorily by the hard sphere model. The microgel structure is different from hard spheres, as the cross-link density decreases with the distance from the particle center leading to a "fuzzy" particle surface with dangling polymer chains. These seem to affect the hydrodynamic interaction much more as compared to direct thermodynamic interaction.

  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. Monte Carlo simulations of in-plane stacking disorder in hard-sphere crystals.

    Science.gov (United States)

    Miedema, P S; de Villeneuve, V W A; Petukhov, A V

    2008-01-01

    On-lattice Monte Carlo simulations of colloidal random-stacking hard-sphere colloidal crystals are presented. The model yields close-packed crystals with random-stacking hexagonal structure. We find a significant amount of in-plane stacking disorder, which slowly anneals in the course of the simulation. The in-plane stacking disorder leads to lateral broadening of the stacking-disorder-induced Bragg rods. It is found that not only the scattering intensity, but also the width is modulated along the Bragg rods.

  14. Morphologically and size uniform monodisperse particles and their shape-directed self-assembly

    Science.gov (United States)

    Collins, Joshua E.; Bell, Howard Y.; Ye, Xingchen; Murray, Christopher Bruce

    2015-11-17

    Monodisperse particles having: a single pure crystalline phase of a rare earth-containing lattice, a uniform three-dimensional size, and a uniform polyhedral morphology are disclosed. Due to their uniform size and shape, the monodisperse particles self assemble into superlattices. The particles may be luminescent particles such as down-converting phosphor particles and up-converting phosphors. The monodisperse particles of the invention have a rare earth-containing lattice which in one embodiment may be an yttrium-containing lattice or in another may be a lanthanide-containing lattice. The monodisperse particles may have different optical properties based on their composition, their size, and/or their morphology (or shape). Also disclosed is a combination of at least two types of monodisperse particles, where each type is a plurality of monodisperse particles having a single pure crystalline phase of a rare earth-containing lattice, a uniform three-dimensional size, and a uniform polyhedral morphology; and where the types of monodisperse particles differ from one another by composition, by size, or by morphology. In a preferred embodiment, the types of monodisperse particles have the same composition but different morphologies. Methods of making and methods of using the monodisperse particles are disclosed.

  15. Morphologically and size uniform monodisperse particles and their shape-directed self-assembly

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Joshua E.; Bell, Howard Y.; Ye, Xingchen; Murray, Christopher Bruce

    2017-09-12

    Monodisperse particles having: a single pure crystalline phase of a rare earth-containing lattice, a uniform three-dimensional size, and a uniform polyhedral morphology are disclosed. Due to their uniform size and shape, the monodisperse particles self assemble into superlattices. The particles may be luminescent particles such as down-converting phosphor particles and up-converting phosphors. The monodisperse particles of the invention have a rare earth-containing lattice which in one embodiment may be an yttrium-containing lattice or in another may be a lanthanide-containing lattice. The monodisperse particles may have different optical properties based on their composition, their size, and/or their morphology (or shape). Also disclosed is a combination of at least two types of monodisperse particles, where each type is a plurality of monodisperse particles having a single pure crystalline phase of a rare earth-containing lattice, a uniform three-dimensional size, and a uniform polyhedral morphology; and where the types of monodisperse particles differ from one another by composition, by size, or by morphology. In a preferred embodiment, the types of monodisperse particles have the same composition but different morphologies. Methods of making and methods of using the monodisperse particles are disclosed.

  16. Synthetic Polymers at Interfaces: Monodisperse Emulsions Multiple Emulsions and Liquid Marbles

    Science.gov (United States)

    Sun, Guanqing

    The adsorption of polymeric materials at interfaces is an energetically favorable process which is investigated in much diversified fields, such as emulsions, bubbles, foams, liquid marbles. Pickering emulsion, which is emulsion stabilized by solid particles has been investigated for over one century and preparation of Pickering emulsion with narrow size distribution is crucial for both the theoretical study of the stabilization mechanism and practical application, such as templated fabrication of colloidosomes. The precise control over the size and functionality of polymer latices allows the preparation of monodisperse Pickering emulsions with desired sizes through SPG membrane emulsification at rather rapid rate compared to microfludic production. Double or multiple emulsions have long been investigated but its rapid destabilization has always been a major obstacle in applying them into practical applications. The modern living polymerization techniques allow us to prepare polymers with designed structure of block copolymers which makes it possible to prepare ultra-stable multiple emulsions. The precise tuning of the ratio of hydrophobic part over the hydrophilic can unveil the stabilization mechanism. Liquid marble is a new type of materials of which liquid droplets are coated by dry particles. The coating of an outer layer of dry particles renders the liquid droplets non-sticky at solid surface which is useful in transportation of small amount of liquid without leakage at extreme low friction force. The property of liquid marbles relies largely on the stabilizers and the drying condition of polymeric latices is shown to have great influence on the property of liquid marbles. Firstly, an introduction to the interfacial and colloidal science with special attention to topics on emulsions, multiple emulsion and liquid marbles is given in Chapter 1. The unique features of an interface and a discussion on the definition of colloids are introduced prior to the

  17. Monodisperse metal nanoparticle catalysts on silica mesoporous supports: synthesis, characterizations, and catalytic reactions

    Energy Technology Data Exchange (ETDEWEB)

    Somorjai, G.A.

    2009-09-14

    The design of high performance catalyst achieving near 100% product selectivity at maximum activity is one of the most important goals in the modern catalytic science research. To this end, the preparation of model catalysts whose catalytic performances can be predicted in a systematic and rational manner is of significant importance, which thereby allows understanding of the molecular ingredients affecting the catalytic performances. We have designed novel 3-dimensional (3D) high surface area model catalysts by the integration of colloidal metal nanoparticles and mesoporous silica supports. Monodisperse colloidal metal NPs with controllable size and shape were synthesized using dendrimers, polymers, or surfactants as the surface stabilizers. The size of Pt, and Rh nanoparticles can be varied from sub 1 nm to 15 nm, while the shape of Pt can be controlled to cube, cuboctahedron, and octahedron. The 3D model catalysts were generated by the incorporation of metal nanoparticles into the pores of mesoporous silica supports via two methods: capillary inclusion (CI) and nanoparticle encapsulation (NE). The former method relies on the sonication-induced inclusion of metal nanoparticles into the pores of mesoporous silica, whereas the latter is performed by the encapsulation of metal nanoparticles during the hydrothermal synthesis of mesoporous silica. The 3D model catalysts were comprehensively characterized by a variety of physical and chemical methods. These catalysts were found to show structure sensitivity in hydrocarbon conversion reactions. The Pt NPs supported on mesoporous SBA-15 silica (Pt/SBA-15) displayed significant particle size sensitivity in ethane hydrogenolysis over the size range of 1-7 nm. The Pt/SBA-15 catalysts also exhibited particle size dependent product selectivity in cyclohexene hydrogenation, crotonaldehyde hydrogenation, and pyrrole hydrogenation. The Rh loaded SBA-15 silica catalyst showed structure sensitivity in CO oxidation reaction. In

  18. Freezing of charged colloids in slit pores.

    Science.gov (United States)

    Grandner, Stefan; Klapp, Sabine H L

    2008-12-28

    Using Monte Carlo simulations in the grand canonical and isobaric ensembles we investigate freezing phenomena in a charged colloidal suspension confined to narrow slit pores. Our model involves only the macroions which interact via a Derjaguin-Landau-Verwey-Overbeek (DLVO) potential supplemented by a soft-sphere potential. We focus on DLVO parameters typical for moderately charged silica particles (with charges Z approximately 35) in solvents of low ionic strengths. The corresponding DLVO interactions are too weak to drive a (bulk) freezing transition. Nevertheless, for sufficiently small surface separations L(z) the confined systems display not only layering but also significant in-plane crystalline order at chemical potentials where the bulk system is a globally stable fluid (capillary freezing). At confinement conditions related to two-layer systems the observed in-plane structures are consistent with those detected in ground state calculations for perfect Yukawa bilayers [R. Messina and H. Lowen, Phys. Rev. Lett. 91, 146101 (2003)]. Here we additionally observe (at fixed L(z)) a compression-induced first-order phase transition from a two-layer to a three-layer system with different in-plane structure, in agreement with previous findings for pure hard spheres.

  19. The nature of the colloidal 'glass' transition.

    Science.gov (United States)

    Dawson, Kenneth A; Lawlor, A; DeGregorio, Paolo; McCullagh, Gavin D; Zaccarelli, Emanuela; Foffi, Giuseppe; Tartaglia, Piero

    2003-01-01

    The dynamically arrested state of matter is discussed in the context of athermal systems, such as the hard sphere colloidal arrest. We believe that the singular dynamical behaviour near arrest expressed, for example, in how the diffusion constant vanishes may be 'universal', in a sense to be discussed in the paper. Based on this we argue the merits of studying the problem with simple lattice models. This, by analogy with the the critical point of the Ising model, should lead us to clarify the questions, and begin the program of establishing the degree of universality to be expected. We deal only with 'ideal' athermal dynamical arrest transitions, such as those found for hard sphere systems. However, it is argued that dynamically available volume (DAV) is the relevant order parameter of the transition, and that universal mechanisms may be well expressed in terms of DAV. For simple lattice models we give examples of simple laws that emerge near the dynamical arrest, emphasising the idea of a near-ideal gas of 'holes', interacting to give the power law diffusion constant scaling near the arrest. We also seek to open the discussion of the possibility of an underlying weak coupling theory of the dynamical arrest transition, based on DAV.

  20. Optical properties of gold nanoshells on monodisperse silica cores: Experiment and simulations

    Science.gov (United States)

    Khanadeev, Vitaly A.; Khlebtsov, Boris N.; Khlebtsov, Nikolai G.

    2017-01-01

    Gold nanoshells (GNSs) on silica cores are widely used in various biomedical applications that need the spectral tunability and controlled absorption/scattering ratio. However, the plasmonic quality of experimental extinction spectra of GNS colloids differs from that predicted by Mie theory. In this work, we fabricated highly monodisperse silica nanospheres to use them further as cores for synthesis of silica/gold nanoshells. Four GNS samples with 116-nm core and gold shell thickness ranging from 16 to 34 nm (116/16, 18, 25, 34) were additionally separated in glycerol gradient solutions to obtain fractions with dominant percentage of single particles or aggregates of various sizes. The separated samples demonstrated extinction spectra with a high extinction maximum to minimum ratio about 3. Optical properties of GNS monomers and aggregates with fixed and random orientations were calculated by Mie theory for polydisperse GNSs, by a generalized multiparticle Mie (GMM) theory for aggregates of separated GNSs, and by the finite-difference time-domain (FDTD) method for aggregates of overlapped GNSs. The extinction spectra of upper fractions from 116/25 and 116/34 samples are shown to be well described by Mie theory for GNSs with polydisperse shell thickness. However, for as prepared 116/16 sample this approach fails because of strong near infrared (NIR) contribution from GNS dimers and trimers. The formation of such aggregates is due to coupling of silica cores at early stages of nanoshell synthesis, thus leading to peanut structures with overlapped gold shells. We suggested TEM-based ensemble model with single particles and small dimer and trimer aggregates, which gives satisfactory agreement between measured and FDTD simulated spectra in the vis-NIR region. Thus, the proposed synthetic technology produces high quality gold nanoshells, which remarkable optical properties are in good agreement with electromagnetic simulations based on TEM data.

  1. Green synthesis and antimicrobial activity of monodisperse silver nanoparticles synthesized using Ginkgo Biloba leaf extract

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Yan-yu [School of Food and Biological Engineering, Shaanxi University of Science & Technology, Xi' an 710021 (China); Yang, Hui, E-mail: 549456369@qq.com [School of Food and Biological Engineering, Shaanxi University of Science & Technology, Xi' an 710021 (China); Wang, Tao [School of Food and Biological Engineering, Shaanxi University of Science & Technology, Xi' an 710021 (China); Wang, Chuang [Department of Highway & Bridge, Shaanxi Railway Institute, Weinan 714000 (China)

    2016-11-25

    Various parts of plants can be used as a raw material for the synthesis of nanoparticles, which is eco-friendly way and does not involve any harmful chemicals. In this project, Ginkgo biloba leaf, an abundantly available medicinal plant in China, was for the first time adopted as a reducing and stabilizing agent to synthesize smaller sized and stable silver nanoparticles (AgNPs). To improve the quality of AgNPs, the reduction was accelerated by changing the concentrations of initial Ag{sup +} (0.02, 0.04, 0.06 and 0.08 mol/L) of the reaction mixture consisting of silver nitrate solution (AgNO{sub 3}) and Ginkgo biloba leaf extract. At pH = 8 and lower AgNO{sub 3} concentration (0.02 mol/L), a colloid consisting of well-dispersed spherical nanoparticles was obtained. The synthesized nanocrystals were successfully characterized by UV–vis and XRD. TEM images revealed the size of the spherical AgNPs ranged between 10–16 nm. FTIR analysis revealed that biological macromolecules with groups of −NH{sub 2}, −OH, and others were distributed on the surface of the nanoparticles. The biosynthesized AgNPs exhibited good antibacterial activities against gram-negative bacteria and gram-positive bacteria. Compared to traditional chemical methods, Ginkgo biloba leaf extract provides an easy green synthetical way. It is anticipated that the biosynthesized AgNPs can be used in areas such as cosmetics, foods and medical applications. - Highlights: • Monodisperse silver nanoparticles were first prepared by a green synthetical way through Ginkgo Biloba leaf extract. • The synthesized AgNPs is of high crystallinity, stable and good dispersion with smaller sizes between 10–16 nm. • The achieved AgNPs exhibits good antibacterial activities. • The biosynthesis method is advantageous for its cost effectiveness, availability, portability, nontoxic and environmentally benign.

  2. Fractal nematic colloids

    Science.gov (United States)

    Hashemi, S. M.; Jagodič, U.; Mozaffari, M. R.; Ejtehadi, M. R.; Muševič, I.; Ravnik, M.

    2017-01-01

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter. PMID:28117325

  3. Fractal nematic colloids

    Science.gov (United States)

    Hashemi, S. M.; Jagodič, U.; Mozaffari, M. R.; Ejtehadi, M. R.; Muševič, I.; Ravnik, M.

    2017-01-01

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter.

  4. Porous TiO2 Assembled from Monodispersed Nanoparticles.

    Science.gov (United States)

    Liu, Xu; Duan, Weijie; Chen, Yan; Jiao, Shihui; Zhao, Yue; Kang, Yutang; Li, Lu; Fang, Zhenxing; Xu, Wei; Pang, Guangsheng

    2016-12-01

    Porous TiO2 were assembled by evaporating or refluxing TiO2 colloid, which was obtained by dispersing the TiO2 nanoparticles with a crystallite size (d XRD) of 3.2 nm into water or ethanol without any additives. Porous transparent bulk TiO2 was obtained by evaporating the TiO2-C2H5OH colloid at room temperature for 2 weeks, while porous TiO2 nanospheres were assembled by refluxing the TiO2-H2O colloid at 80 °C for 36 h. Both of the porous TiO2 architectures were pore-size-adjustable depending on the further treating temperature. Porous TiO2 nanospheres exhibited enhanced photocatalysis activity compared to the nanoparticles.

  5. Porous TiO2 Assembled from Monodispersed Nanoparticles

    OpenAIRE

    Liu, Xu; Duan, Weijie; Chen, Yan; Jiao, Shihui; Zhao, Yue; Kang, Yutang; Li, Lu; Fang, Zhenxing; Xu, Wei; Pang, Guangsheng

    2016-01-01

    Porous TiO2 were assembled by evaporating or refluxing TiO2 colloid, which was obtained by dispersing the TiO2 nanoparticles with a crystallite size (d XRD) of 3.2 nm into water or ethanol without any additives. Porous transparent bulk TiO2 was obtained by evaporating the TiO2-C2H5OH colloid at room temperature for 2 weeks, while porous TiO2 nanospheres were assembled by refluxing the TiO2-H2O colloid at 80 °C for 36 h. Both of the porous TiO2 architectures were pore-size-adjustable depending...

  6. Panoramic stereo sphere vision

    Science.gov (United States)

    Feng, Weijia; Zhang, Baofeng; Röning, Juha; Zong, Xiaoning; Yi, Tian

    2013-01-01

    Conventional stereo vision systems have a small field of view (FOV) which limits their usefulness for certain applications. While panorama vision is able to "see" in all directions of the observation space, scene depth information is missed because of the mapping from 3D reference coordinates to 2D panoramic image. In this paper, we present an innovative vision system which builds by a special combined fish-eye lenses module, and is capable of producing 3D coordinate information from the whole global observation space and acquiring no blind area 360°×360° panoramic image simultaneously just using single vision equipment with one time static shooting. It is called Panoramic Stereo Sphere Vision (PSSV). We proposed the geometric model, mathematic model and parameters calibration method in this paper. Specifically, video surveillance, robotic autonomous navigation, virtual reality, driving assistance, multiple maneuvering target tracking, automatic mapping of environments and attitude estimation are some of the applications which will benefit from PSSV.

  7. 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

  8. 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.

  9. Structural disorder versus spin canting in monodisperse maghemite nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Kubickova, S.; Vejpravova, J., E-mail: vejpravo@fzu.cz [Department of Magnetic Nanosystems, Institute of Physics of the ASCR, v.v.i., Na Slovance 2, 182 21 Prague (Czech Republic); Niznansky, D. [Faculty of Science, Department of Inorganic Chemistry, Charles University in Prague, Albertov 2030, 128 40 Prague (Czech Republic); Morales Herrero, M. P. [Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Ins de la Cruz 3, Campus de Cantoblanco, 28049 Madrid (Spain); Salas, G. [Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Ins de la Cruz 3, Campus de Cantoblanco, 28049 Madrid (Spain); Instituto Madrileno de Estudios Avanzados en Nanociencia, Campus Universitario de Cantoblanco, 28049 Madrid (Spain)

    2014-06-02

    Monodisperse maghemite nanoparticles with diameter ranging from 7 to 20 nm were examined by the In-field Mössbauer Spectroscopy (IFMS) in varying external magnetic field up to 6 T. Surprisingly, the small-sized particles (7 nm) exhibit nearly no spin canting in contrast to the larger particles with lower surface-to-volume ratio. We demonstrate that the observed phenomenon is originated by lower relative crystallinity of the larger particles with different internal structure. Hence, the persistence of the 2nd and 5th absorption lines in the IFMS cannot be unambiguously assigned to the surface spins.

  10. MONODISPERSE MICRON-SIZED POLYACRYLAMIDE PARTICLES SYNTHESIZED BY DISPERSION POLYMERIZATION

    Institute of Scientific and Technical Information of China (English)

    Xin Hou; Bo Gao; Zhe-guo Zhang; Kang-de Yao

    2007-01-01

    Monodisperse micron-sized polyacrylamide (PAM) particles with a regular shape have been successfully prepared through dispersion polymerization of the monomer using a rotary reactor. FTIR and NMR spectroscopic results demonstrated the formation of PAM. POM and TEM observations revealed that PAM particles had a regular shape and good dispersity. A thick layer of surfactant (PVP) still existed on PAM particles after multiple centrifugation and ultrasonic re-dispersion in ethanol, which indicates a strong interaction between PVP and PAM. The effects of various polymerization factors on the average size of PAM particles have also been studied.

  11. 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

  12. Assembly of body-centered cubic crystals in hard spheres.

    Science.gov (United States)

    Xu, W-S; Sun, Z-Y; An, L-J

    2011-05-01

    We investigate the crystallization of monodisperse hard spheres confined by two square patterned substrates (possessing the basic character of the body-centered cubic (bcc) crystal structure) at varying substrate separations via molecular dynamics simulation. Through slowly increasing the density of the system, we find that crystallization under the influence of square patterned substrates can set in at lower densities compared with the homogeneous crystallization. As the substrate separation decreases, the density, where crystallization occurs (i.e., pressure drops), becomes small. Moreover, two distinct regimes are identified in the plane of bcc particle fraction and density for the separation range investigated. For large substrate separations, the bcc particle fraction displays a local maximum as the density is increased, and the resulting formed crystals have a polycrystalline structure. However, and more importantly, another situation emerges for small substrate separations: the capillary effects (stemming from the presence of two substrates) overwhelm the bulk driving forces (stemming from the spontaneous thermal fluctuations in the bulk) during the densification, eventually resulting in the formation of a defect-free bcc crystal (unstable with respect to the bulk hard-sphere crystals) by using two square patterned substrates.

  13. Nonequilibrium condensation and coarsening of field-driven dipolar colloids.

    Science.gov (United States)

    Jäger, Sebastian; Schmidle, Heiko; Klapp, Sabine H L

    2012-07-01

    In colloidal suspensions, self-organization processes can be easily fueled by external fields. Here we consider monolayers of particles with permanent dipole moments that are driven by rotating external fields. In recent experiments, it has been shown that the particles in such systems self-organize into two-dimensional clusters. Here we report results from a computer simulation study of these pattern forming systems. Specifically, we employ Langevin dynamics simulations, Brownian dynamics simulations that include hydrodynamic interactions, and Wang-Landau Monte Carlo simulations of soft spheres interacting via dipolar potentials. We investigate at which field strengths and frequencies clusters form and explore the influence of hydrodynamic interactions. We also examine the phase behavior of the equilibrium system resulting from a time average of the colloidal interactions in the rotating field. In this way we demonstrate that the clustering described in the driven system arises from a first-order phase transition between a vapor and a condensed phase.

  14. Synthesis and optical properties of colloidal gold nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen Ngoc Long; Le Van Vu; Chu Dinh Kiem; Sai Cong Doanh; Cao Thi Nguyet; Pham Thi Hang; Nguyen Duy Thien; Luu Manh Quynh [Faculty of Physics, Hanoi University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi (Viet Nam)], E-mail: longnn@vnu.edu.vn

    2009-09-01

    Colloidal gold nanoparticles (spheres) have been prepared from HAuCl{sub 4} containing aqueous solution by using X-ray irradiation and by chemical reduction method. Gold nanorods were synthesized according to the seed-mediated growth method. The colloidal gold nanoparticles were characterized by using transmission electron microscopy, X-ray diffraction, and UV-VIS absorption spectroscopy. It was found that the concentration of the precursors affects the size of the nanoparticles. In the chemical reduction approach the size of nanoparticles can be controlled by varying amount of trisodium citrate, but in the photochemical method the size of nanoparticles can been controlled by varying the ratio of HAuCl{sub 4} to TX-100 and X-ray irradiation duration. Gold nanorods have been synthesized according to the seed-mediated growth method with two steps. The effect of silver acetate and CTAB on formation of gold nanorods has been studied.

  15. Gelation transitions of colloidal systems with bridging attractions

    Science.gov (United States)

    Yuan, Guangcui; Luo, Junhua; Han, Charles C.; Liu, Yun

    2016-10-01

    Gelation transitions in a colloidal system, where there is a strong reversible attraction between small, soft microgels and large, hard spheres, are systematically investigated. Different from widely studied depletion attraction systems that are also two-component systems, the strong attraction between small solvent and large solute particles introduces bridging attractions between large solute particles. We conclusively demonstrate that the formation of physical gels at the intermediate volume fraction of our bridging attraction system follows more closely with the percolation line that is in stark contrast to what is observed in depletion attraction systems, where the gelation transition is related with the frustrated spinodal separation, not a purely kinetic phenomenon. Our results introduce a different way to control gelation transitions in spherical colloidal systems, and imply that people need to be prudent when generalizing the physical picture of the gelation transitions obtained from systems with different origins of effective attraction as the solvent molecule may play important roles.

  16. Sulfur/graphitic hollow carbon sphere nano-composite as a cathode material for high-power lithium-sulfur battery.

    Science.gov (United States)

    Shin, Eon Sung; Kim, Min-Seop; Cho, Won Il; Oh, Si Hyoung

    2013-08-03

    The intrinsic low conductivity of sulfur which leads to a low performance at a high current rate is one of the most limiting factors for the commercialization of lithium-sulfur battery. Here, we present an easy and convenient method to synthesize a mono-dispersed hollow carbon sphere with a thin graphitic wall which can be utilized as a support with a good electrical conductivity for the preparation of sulfur/carbon nano-composite cathode. The hollow carbon sphere was prepared from the pyrolysis of the homogenous mixture of the mono-dispersed spherical silica and Fe-phthalocyanine powder in elevated temperature. The composite cathode was manufactured by infiltrating sulfur melt into the inner side of the graphitic wall. The electrochemical cycling shows a capacity of 425 mAh g-1 at 3 C current rate which is more than five times larger than that for the sulfur/carbon black nano-composite prepared by simple ball milling.

  17. Haphazard Packing of Unequal Spheres

    Institute of Scientific and Technical Information of China (English)

    叶大年; 张金民

    1991-01-01

    Haphazard packing of equal and unequal spheres can be performed for the spheres of molecular sieve material with a density of 1.80.The packing of such spheres in air is equivalent to that of nat-ural grains in water.Packing concentrations of equal spheres have been obtained for different pac-king intensities.Unequal spheres can be regarded as equal ones in a wide range of diameter ratios,so far as the packing concentration is concerned.A threshold of diameter ratio exists at 0.70,be-low which the packing concentration is expected to increase.The variation curves of concentration vs.diameter ratio were established in the experiment.The result will help us to understand the process of sedimentation and the concentration of voids in sedimentary rocks.

  18. A novel method for preparing monodispersed polystyrene nanoparticles

    Institute of Scientific and Technical Information of China (English)

    LIU Kaiyi; WANG Zhaoqun

    2007-01-01

    A preparation manner for monodispersed polystyrene(PS)nanoparticles polymerized by using a novel addition procedure of a monomer is suggested.In systems containing a smaller amount of surfactant compared with conventional microemulsion polymerization,the polymerization processes consists of three stages:adding dropwise the first part of the monomer for a few minutes at 80℃ and polymerizing for 1 h;adding collectively the residual part of the monomer and polymerizing at the same temperature for another 1 h;and then polymerizing at 85℃ for another 1 h.Based on discussions on the nucleation mechanism of particles in the polymerization system,the influences of monomer weight added dropwise,and amounts of initiator and emulsifier on the size and distribution of PS particles were investigated.PS nanoparticles with smaller diameter such as a number-average diameter of 18.7 nm and better monodispersity were obtained since the dropped styrene amount was suitable under 20wt-% emulsifier amount and 3wt-% initiator amount based on the monomer.

  19. Enhanced shear separation for chiral magnetic colloidal aggregates.

    Science.gov (United States)

    Mendoza, C I; Marques, C M; Thalmann, F

    2010-12-01

    We study the designing principles of the simplest colloidal propeller, an architecture built from four identical spheres that can couple translation with rotation to produce controlled drift motion. By considering superparamagnetic beads, we show that the simultaneous action of a magnetic field and a shear flow leads to the migration of the cluster in the vorticity direction. We investigate the dependence of the migration velocity on the geometrical parameters of the cluster and find that significant cluster separation can be achieved under the typical operation conditions of microfluidic devices.

  20. Self-assembly of polloids from flattened colloids to strong and flexible chains

    Science.gov (United States)

    Ramirez, Laura Mely

    The field of colloidal science has been exploited for decades due to the intriguing properties and versatile applicability of colloids in numerous natural and industrial processes. In fact, colloidal particles serve as building blocks for complex assemblies that hold great promise in modeling important molecular interactions. Visualization and dynamic testing of molecular systems is limited by their characteristic rapid time scales and small length scales. In this dissertation, "colloidal monomers" are spontaneously self-assembled into strong and flexible chains through a designed particle-binding mechanism that is tunable. No external force field is applied during the assembly process. These colloidal polymers -- polloids -- aim to study the dynamics and polymerization of real polymers that exhibit both durable and reversible bonds. The monomers in polloids consist of micron-size particles with a small physical deformation, a localized flat region. By tuning the ionic strength of the solution, a flat region on one particle can preferentially bond to either the flat region or the spherical part of another particle. The increase in the effective interaction area strengthens the bond into a deep secondary energy minimum, where a thin layer of fluid lies in between the two particles and allows full bond rotation. The main contributions of this research are 1) a DLVO model that predicts the interparticle potential as a function of separation distance between two particles facing flat-flat, flat-sphere, or sphere-sphere, the latter being the usual DLVO potential, 2) a controlled technique to create localized flat regions on spherical colloids with a model that predicts the growth of the flat radius with time, 3) the three-dimensional visualization of polloids in solution mimicking polymers, and 4) the data analysis showing how the distributions of chain length and weight follow closely classical condensation polymerization. Hence, polloids could impact the way

  1. Interchain tube pressure effect in extensional flows of oligomer diluted nearly monodisperse polystyrene melts

    DEFF Research Database (Denmark)

    Rasmussen, Henrik K.; Huang, Qian

    2014-01-01

    We have derived a constitutive equation to explain the extensional dynamics of oligomer-diluted monodisperse polymers, if the length of the diluent has at least two Kuhn steps. These polymer systems have a flow dynamics which distinguish from pure monodisperse melts and solutions thereof, if the ...

  2. Monodisperse Femto- to Atto-liter Droplet Formation Using a Nano-Microchannel Interface

    NARCIS (Netherlands)

    Shui, Lingling; Berg, van den Albert; Eijkel, Jan C.T.; Kim, Tae Song; Lee, Yoon-Sik; Chung, Taek-Dong; Jeon, Noo Li; Suh, Kahp-Yang; Choo, Jaebum; Kim, Yong-Kweon

    2009-01-01

    We demonstrate the production of sub-micrometer diameter monodisperse droplets by using a nano-micro channel interface. A perfectly steady nanoscopic liquid filament can be formed by a geometric confinement which eventually gives rise to a stable production of nearly perfectly monodisperse droplets.

  3. Surface properties of poly(ethylene oxide)-based segmented block copolymers with monodisperse hard segments

    NARCIS (Netherlands)

    Husken, D.; Feijen, Jan; Gaymans, R.J.

    2009-01-01

    The surface properties of segmented block copolymers based on poly(ethylene oxide) (PEO) segments and monodisperse crystallizable tetra-amide segments were studied. The monodisperse crystallizable segments (T6T6T) were based on terephthalate (T) and hexamethylenediamine (6). Due to the crystallinity

  4. Facile preparation and visible light photocatalytic activity of CdIn{sub 2}S{sub 4} monodispersed spherical particles

    Energy Technology Data Exchange (ETDEWEB)

    Mu Jin, E-mail: mujin@sit.edu.cn [School of Chemical and Environmental Engineering, Shanghai Institute of Technology, 100 Haiquan Road, Shanghai 201418 (China); Wei Qinglian; Yao Pingping; Zhao Xueling [School of Chemistry and Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China); Kang Shizhao; Li Xiangqing [School of Chemical and Environmental Engineering, Shanghai Institute of Technology, 100 Haiquan Road, Shanghai 201418 (China)

    2012-02-05

    Highlights: Black-Right-Pointing-Pointer CdIn{sub 2}S{sub 4} monodispersed spherical particles were prepared by a soft solution method. Black-Right-Pointing-Pointer Mercaptoacetic acid was used as capping agent to hinder the fast crystal growth. Black-Right-Pointing-Pointer Thioacetamide as sulfur source resulted in the slow growth of particles. Black-Right-Pointing-Pointer CdIn{sub 2}S{sub 4} spheres showed high visible light photocatalytic activity. - Abstract: We developed a facile method to prepare CdIn{sub 2}S{sub 4} monodispersed spherical particles by using mercaptoacetic acid as capping agent and thioacetamide as sulfur source. The results indicated that the size and morphology of CdIn{sub 2}S{sub 4} particles were related to reaction time. The CdIn{sub 2}S{sub 4} spherical particles with an average size of about 236 nm and a narrow size distribution were formed after reacting for 7 h. The photocatalytic activity of as-synthesized CdIn{sub 2}S{sub 4} spherical particles was evaluated by the photocatalytic degradation of methyl orange under visible light illumination. The results showed that the photocatalytic activity increased with prolonging reaction time in the preparation of CdIn{sub 2}S{sub 4} spherical particles. The CdIn{sub 2}S{sub 4} spherical particles prepared after reacting for 7 h exhibited a 98% degradation efficiency of methyl orange after 15 min visible light irradiation.

  5. Monodisperse and inorganically capped Sn and Sn/SnO2 nanocrystals for high-performance Li-ion battery anodes.

    Science.gov (United States)

    Kravchyk, Kostiantyn; Protesescu, Loredana; Bodnarchuk, Maryna I; Krumeich, Frank; Yarema, Maksym; Walter, Marc; Guntlin, Christoph; Kovalenko, Maksym V

    2013-03-20

    We report a facile synthesis of highly monodisperse colloidal Sn and Sn/SnO2 nanocrystals with mean sizes tunable over the range 9-23 nm and size distributions below 10%. For testing the utility of Sn/SnO2 nanocrystals as an active anode material in Li-ion batteries, a simple ligand-exchange procedure using inorganic capping ligands was applied to facilitate electronic connectivity within the components of the nanocrystalline electrode. Electrochemical measurements demonstrated that 10 nm Sn/SnO2 nanocrystals enable high Li insertion/removal cycling stability, in striking contrast to commercial 100-150 nm powders of Sn and SnO2. In particular, reversible Li-storage capacities above 700 mA h g(-1) were obtained after 100 cycles of deep charging (0.005-2 V) at a relatively high current of 1000 mA h g(-1).

  6. Isentropic Spheres in General Relativity

    CERN Document Server

    Humi, Mayer

    2016-01-01

    Astrophysical gas clouds undergo thermodynamically irreversible processes and emit heat to their surroundings. Due the emission of this heat one can envision an idealized situation in which gas entropy remains (almost) constant. With this motivation in mind we derive in this paper interior solutions to the Einstein equations of General Relativity for spheres which consist of isentropic gas. In particular we investigate solutions in which the mass distribution inside the sphere has several shells. Such spheres might be considered an early stage for the formation of a "solar system".

  7. Polymers and colloids

    Energy Technology Data Exchange (ETDEWEB)

    Schurtenberger, P. [ETH Zurich, Inst. fuer Polymere, Zurich (Switzerland)

    1996-11-01

    A wealth of structural information from colloid and polymer solutions on a large range of length scales can be obtained using small angle neutron scattering (SANS) experiments. After a general introduction to the field of soft condensed matter, I shall give a few selected examples on how SANS combined with suitable contrast variation schemes can be used to extract information on the size and conformation of polymer coils in solution and in the melt, and on the local structure and flexibility of polymerlike micelles and microemulsions. (author) 8 figs., tabs., 44 refs.

  8. Preparation and characterization of silver colloids with different morphologies under ultrasonic field

    Institute of Scientific and Technical Information of China (English)

    Cheng Jingquan; Yao Suwei; Zhang Weiguo; Zou Yi

    2006-01-01

    In the ultrasonic field,stable silver colloids were produced by the reduction of AgNO3 with the protection of PVP using KBH4 or N2H4.H2O as reductant.The main factors affecting the morphology of silver nanoparticles,such as distribution of the ultrasonic field,ultrasonic time,ultrasonic power,and the species of reductant,were studied.The silver colloids were identified by TEM and spectrophotometry.The results indicate that the factors such as distribution of the ultrasonic field,ultrasonic time,ultrasonic power,and the species of reductant have a great impact on the morphology of the silver nanoparticles.The size of the silver nanoparticles decreases with the ultrasonic power and ultrasonic time increasing.Ag nanoparticles prepared in standing wave field preferentially grow in a certain direction,which is propitious for forming hexagonal- and spherical-like silver nanoparticles.Monodispersed spherical silver nanoparticles are easily synthesized in the diffusion field.The stability of silver colloid becomes improved by ultrasonic treatment.For example,precipitate is not found after several weeks for the silver colloid prepared with an ultrasonic treatment time of 180 min.The silver nanoparticles prepared without ultrasonic treatment are large spherical-like and hexagonal.Well-dispersed spherical silver particles with a mean size of about 20 nm have been prepared under ultrasonic treatment.Spherical,spherical-like,and hexagonal silver nanoparticles can be obtained by changing the reductants..

  9. Influence of porous media structure in colloid retention in the absence of an energy barrier

    Science.gov (United States)

    Pazmino, E. F.; Johnson, W. P.; Ma, H.

    2010-12-01

    Many colloid transport experiments have been conducted in a porous media with narrow size distribution, which allows a single collector size to be used in filtration theory to predict deposition rates. In this work, deposition of colloids (ranging from 0.21 μm to 9.1 μm) in packed columns is examined in the absence of an energy barrier with three different glass bead porous media: uniform mono-dispersed, mono-modal poly-dispersed and bimodal poly-dispersed. The corresponding porosities to these media are 0.378, 0.339 and 0.282. The effect of gravitational settling on deposition is studied by injecting the particles co-current and counter-current with gravity, especially for larger size colloids. Also, direct observations are conducted in a flow cell for selected colloid sizes for a better understanding of the mechanisms of attachment. Experimental results are compared with theoretical predictions to determine characteristic collector sizes that represent poly-dispersed porous media in filtration theory.

  10. Crystallization kinetics of colloidal binary mixtures with depletion attraction.

    Science.gov (United States)

    Kozina, Anna; Díaz-Leyva, Pedro; Palberg, Thomas; Bartsch, Eckhard

    2014-12-21

    In this work the crystallization kinetics of colloidal binary mixtures with attractive interaction potential (Asakura-Oosawa) has been addressed. Parameters such as fraction of crystals, linear crystal dimension and crystal packing have been quantified in order to understand how the crystal formation is driven in terms of the depth of the attractive potential and the composition of the binary mixture (described by the number ratio). It was found that inside the eutectic triangle, crystallization is mainly governed by nucleation and the crystal packing is close to the close-packing of hard spheres. Moving out from the eutectic triangle towards small component results in the crystallization of small spheres. Enrichment of the eutectic mixture with large component results in the crystallization of both large and small spheres, however, the kinetics are completely different from those of the eutectic composition. Crosslinked polystyrene microgels with nearly hard sphere interactions were used as model systems. Attraction was introduced by addition of linear polystyrene. The time evolution of crystallization has been followed by static light scattering.

  11. Aerosol printing of colloidal nanocrystals by aerodynamic focusing

    Science.gov (United States)

    Qi, Lejun

    Colloidal semiconductor nanocrystals, or quantum dots, have shown promise as the active material in electronic and optoelectronic applications, because of their high quantum yield, narrow spectral emission band, size-tunable bandgap, chemical stability, and easy processibility. Meanwhile, it is still challenging to print patterns of nanocrystal films with desired linewidth and thickness, which is a critical step in fabrication of nanocrystal-based devices. In this thesis, a direct-write method of colloidal semiconductor nanocrystals has been developed. Like other direct-write techniques, this aerosol based method simplifies printing process and reduces the manufacturing cost, as it avoids mask screening, lithography, and pre-patterning of the substrate. Moreover, the aerosol printing with aerodynamic lenses needs neither microscale nozzles nor sheath gases, and is able to incorporate into the vacuum systems currently used in microelectronic fabrication. This thesis research presents systematic efforts to develop an aerosol-based method to directly write patterns of semiconductor nanocrystals from colloidal dispersions by aerodynamic focusing. First, the synthesized colloidal nanocrystals in hexane were nebulized into compact and spherical agglomerates suspending in the carrier gas. The details about the impact dynamics of individual aerosolized nanocrystal agglomerates were investigated. As building blocks of printed nanocrystal films, the agglomerate exhibited cohesive and granular behaviors during impact deformation on the substrate. The strength of cohesion between nanocrystals in the agglomerates could be adjusted by tuning the number concentration of colloidal nanocrystal dispersion. Second, ultrathin films of nanocrystals were obtained by printing monodisperse nanocrystal agglomerates. As the result of the granular property of nanocrystal agglomerates, it was found that the thickness of deposited agglomerates strongly depended on the size of agglomerates. A

  12. A synchrotron small-angle X-ray scattering study of order/disorder in colloidal crystals

    NARCIS (Netherlands)

    Dolbnya, Igor Petrovich

    2004-01-01

    The present work reports results of a detailed x-ray diffraction study of the structure and long-range order of colloidal crystals, self-grown in suspensions of quartz spheres with diameter of about a quarter of a micron. The crystals are found to consist of a randomly-stacked sequence of hexagonal

  13. Double hexagonal close-packed structure revealed in a single colloidal crystal grain by Bragg rod analysis

    NARCIS (Netherlands)

    Meijer, J. M.; Shabalin, A.; Dronyak, R.; Yefanov, O. M.; Singer, A.; Kurta, R. P.; Lorenz, U.; Gorobstov, O.; Dzhigaev, D.; Gulden, J.; Byelov, D. V.; Zozulya, A. V.; Sprung, M.; Vartanyants, I. A.; Petukhov, Andrei V.

    2014-01-01

    A coherent X-ray diffraction study of a single colloidal crystal grain composed of silica spheres is reported. The diffraction data contain Bragg peaks and additional features in the form of Bragg rods, which are related to the stacking of the hexagonally close-packed layers. The profile of the Brag

  14. EDITORIAL: Colloidal dispersions in external fields Colloidal dispersions in external fields

    Science.gov (United States)

    Löwen, Hartmut

    2012-11-01

    , Ojeda-Lopez M A and Arauz-Lara J L 2012 J. Phys. Condens. Matter 24 464126 [31]Leferink op Reinink A B G M, van den Pol E, Byelov D V, Petukhov A V and Vroege G J 2012 J. Phys. Condens. Matter 24 464127 [32]Taylor S L, Evans R and Royall C P 2012 J. Phys. Condens. Matter 24 464128 [33]Toner J, Tu Y H and Ramaswamy S 2012 J. Phys. Condens. Matter 24 464110 [34]Schmitz R and Dünweg B 2005 J. Phys. Condens. Matter 318 170 [35]Cates M E 2012 Rep. Prog. Phys. 75 042601 [36]Tarama M and Ohta T 2012 J. Phys. Condens. Matter 24 464129 [37]Wensink H H and Löwen H 2012 J. Phys. Condens. Matter 24 464130 Colloidal dispersions in external fields contents Colloidal dispersions in external fieldsHartmut Löwen Depletion induced clustering in mixtures of colloidal spheres and fd-virusD Guu, J K G Dhont, G A Vliegenthart and M P Lettinga Advanced rheological characterization of soft colloidal model systemsS Gupta, S K Kundu, J Stellbrink, L Willner, J Allgaier and D Richter Conformational and dynamical properties of ultra-soft colloids in semi-dilute solutions under shear flowSunil P Singh, Dmitry A Fedosov, Apratim Chatterji, Roland G Winkler and Gerhard Gompper Transient dynamics in dense colloidal suspensions under shear: shear rate dependenceM Laurati, K J Mutch, N Koumakis, J Zausch, C P Amann, A B Schofield, G Petekidis, J F Brady, J Horbach, M Fuchs and S U Egelhaaf Force-induced diffusion in microrheologyCh J Harrer, D Winter, J Horbach, M Fuchs and Th Voigtmann Micro-macro-discrepancies in nonlinear microrheology: I. Quantifying mechanisms in a suspension of Brownian ellipsoidsRyan J DePuit and Todd M Squires Micro-macro discrepancies in nonlinear microrheology: II. Effect of probe shapeRyan J DePuit and Todd M Squires Viscosity of electrolyte solutions: a mode-coupling theoryClaudio Contreras-Aburto and Gerhard Nägele Electro-kinetics of charged-sphere suspensions explored by integral low-angle super-heterodyne laser Doppler velocimetryThomas Palberg, Tetyana K

  15. Synthesis of Cone-Shaped Colloids from Rod-Like Silica Colloids with a Gradient in the Etching Rate.

    Science.gov (United States)

    Hagemans, Fabian; van der Wee, Ernest B; van Blaaderen, Alfons; Imhof, Arnout

    2016-04-26

    We present the synthesis of monodisperse cone-shaped silica colloids and their fluorescent labeling. Rod-like silica colloids prepared by ammonia-catalyzed hydrolysis and condensation of tetraethyl orthosilicate in water droplets containing polyvinylpyrrolidone cross-linked by citrate ions in pentanol were found to transform into cone-shaped particles upon mild etching by NaOH in water. The diameter and length of the resulting particles were determined by those of the initial rod-like silica colloids. The mechanism responsible for the cone-shape involves silica etching taking place with a varying rate along the length of the particle. Our experiments thus also lead to new insights into the variation of the local particle structure and composition. These are found to vary gradually along the length of the rod, as a result of the way the rod grows out of a water droplet that keeps itself attached to the flat end of the bullet-shaped particles. Subtle differences in composition and structure could also be resolved by high-resolution stimulated emission depletion confocal microscopy on fluorescently labeled particles. The incorporation of a fluorescent dye chemically attached to an amine-based silane coupling agent resulted in a distribution of fluorophores mainly on the outside of the rod-shaped particles. In contrast, incorporation of the silane coupling agent alone resulted in a homogeneous distribution. Additionally, we show that etching rods, where a silane coupling agent alone was incorporated and subsequently coupled to a fluorescent dye, resulted in fluorescent silica cones, the orientation of which can be discerned using super-resolution confocal microscopy.

  16. Dyson Spheres around White Dwarfs

    CERN Document Server

    Semiz, İbrahim

    2015-01-01

    A Dyson Sphere is a hypothetical structure that an advanced civilization might build around a star to intercept all of the star's light for its energy needs. One usually thinks of it as a spherical shell about one astronomical unit (AU) in radius, and surrounding a more or less Sun-like star; and might be detectable as an infrared point source. We point out that Dyson Spheres could also be built around white dwarfs. This type would avoid the need for artificial gravity technology, in contrast to the AU-scale Dyson Spheres. In fact, we show that parameters can be found to build Dyson Spheres suitable --temperature- and gravity-wise-- for human habitation. This type would be much harder to detect.

  17. Data compression on the sphere

    CERN Document Server

    McEwen, J D; Eyers, D M; 10.1051/0004-6361/201015728

    2011-01-01

    Large data-sets defined on the sphere arise in many fields. In particular, recent and forthcoming observations of the anisotropies of the cosmic microwave background (CMB) made on the celestial sphere contain approximately three and fifty mega-pixels respectively. The compression of such data is therefore becoming increasingly important. We develop algorithms to compress data defined on the sphere. A Haar wavelet transform on the sphere is used as an energy compression stage to reduce the entropy of the data, followed by Huffman and run-length encoding stages. Lossless and lossy compression algorithms are developed. We evaluate compression performance on simulated CMB data, Earth topography data and environmental illumination maps used in computer graphics. The CMB data can be compressed to approximately 40% of its original size for essentially no loss to the cosmological information content of the data, and to approximately 20% if a small cosmological information loss is tolerated. For the topographic and il...

  18. MONODISPERSED AND NANOSIZED DENDRIMER/POLYSTYRENE LATEX PARTICLES

    Institute of Scientific and Technical Information of China (English)

    Changfeng Yi; Zushun Xu; Warren T. Ford

    2004-01-01

    Emulsion polymerization of styrene was carried out using dendrimer DAB-dendr-(NH2)64 as seed. The size and size distribution of the emulsion particles were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the effects of emulsion polymerization conditions on the preparation of emulsion particle were investigated. It has been found that the nanosized dendrimer/polystyrene polymer emulsion particles obtained were in the range of 26~64 nm in diameter, and were monodisperse; the size and size distribution of emulsion particles were influenced by the contents of dendrimer DAB-dendr-(NH2)64, emulsifier and initiator, as well as the pH value.

  19. Selection of quasi-monodisperse super-micron aerosol particles

    Science.gov (United States)

    Rösch, Michael; Pfeifer, Sascha; Wiedensohler, Alfred; Stratmann, Frank

    2014-05-01

    Size-segregated quasi monodisperse particles are essential for e.g. fundamental research concerning cloud microphysical processes. Commonly a DMA (Differential Mobility Analyzer) is used to produce quasi-monodisperse submicron particles. Thereto first, polydisperse aerosol particles are bipolarly charged by a neutralizer, and then selected according to their electrical mobility with the DMA [Knutson et al. 1975]. Selecting a certain electrical mobility with a DMA results in a particle size distribution, which contains singly charged particles as well as undesired multiply charged larger particles. Often these larger particles need to either be removed from the generated aerosol or their signals have to be corrected for in the data inversion and interpretation process. This problem becomes even more serious when considering super-micron particles. Here we will present two different techniques for generating quasi-monodisperse super-micron aerosol particles with no or only an insignificant number of larger sized particles being present. First, we use a combination of a cyclone with adjustable aerodynamic cut-off diameter and our custom-built Maxi-DMA [Raddatz et al. 2013]. The cyclone removes particles larger than the desired ones prior to mobility selection with the DMA. This results in a reduction of the number of multiply charged particles of up to 99.8%. Second, we utilize a new combination of cyclone and PCVI (Pumped Counterflow Virtual Impactor), which is based on purely inertial separation and avoids particle charging. The PCVI instrument was previously described by Boulter et al. (2006) and Kulkarni et al. (2011). With our two setups we are able to produce quasi-monodisperse aerosol particles in the diameter range from 0.5 to 4.4 µm without a significant number of larger undesired particles being present. Acknowledgements: This work was done within the framework of the DFG funded Ice Nucleation research UnIT (INUIT, FOR 1525) under WE 4722/1-1. References

  20. Solvent: A Key in Digestive Ripening for Monodisperse Au Nanoparticles

    Science.gov (United States)

    Wang, Peng; Qi, Xuan; Zhang, Xuemin; Wang, Tieqiang; Li, Yunong; Zhang, Kai; Zhao, Shuang; Zhou, Jun; Fu, Yu

    2017-01-01

    This work has mainly investigated the influence of the solvent on the nanoparticles distribution in digestive ripening. The experiments suggested that the solvents played a key role in digestive ripening of Au nanoparticles (Au NPs). For the benzol solvents, the resulting size distribution of Au NPs was inversely related to the solvent polarity. It may be interpreted by the low Gibbs free energy of nanoparticles in the high polarity medium, which was supposedly in favor of reducing the nanoparticles distribution. Through digestive ripening in the highly polar benzol solvent of p-chlorotoluene, monodisperse Au NPs with relative standard deviation (RSD) of 4.8% were achieved. This indicated that digestive ripening was an effective and practical way to prepare high-quality nanoparticles, which holds great promise for the nanoscience and nanotechnology.

  1. Controllable synthesis of nitrogen-doped hollow mesoporous carbon spheres using ionic liquids as template for supercapacitors

    Science.gov (United States)

    Chen, Aibing; Li, Yunqian; Liu, Lei; Yu, Yifeng; Xia, Kechan; Wang, Yuying; Li, Shuhui

    2017-01-01

    We have demonstrated a facile and controllable synthesis of monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) using resorcinol/formaldehyde resin as a carbon precursor, tetraethyl orthosilicate as a structure-assistant agent, ionic liquids (ILs) as soft template, partial carbon sources, and nitrogen sources. The sizes and the architectures including hollow and yolk-shell of resultant carbon spheres can be efficiently controlled through the adjustment of the content of ILs. Alkyl chain length of the ILs also has an important effect on the formation of N-HMCSs. With proper alkyl chain length and content of ILs, the resultant N-HMCSs show monodispersed hollow spheres with high surface areas (up to 1158 m2 g-1), large pore volumes (up to 1.70 cm3 g-1), and uniform mesopore size (5.0 nm). Combining the hollow mesoporous structure, high porosity, large surface area, and nitrogen functionality, the as-synthesized N-HMCSs have good supercapacitor performance with good capacitance (up to 159 F g-1) and favorable capacitance retention (88% capacitive retention after 5000 cycles).

  2. Concentrations of inertial particles in the turbulent wake of an immobile sphere

    CERN Document Server

    Homann, Holger

    2015-01-01

    Direct numerical simulations are used to study the interaction of a stream of small heavy inertial particles with the laminar and turbulent wakes of an immobile sphere facing an incompressible uniform inflow. Particles that do not collide with the obstacle but move past it, are found to form preferential concentrations both in the sphere boundary layer and in its wake. In the laminar case, the upstream diverging flow pattern is responsible for particle clustering on a cylinder that extends far downstream the sphere. The interior of this surface contains no particles and can be seen as a shadow of the large obstacle. Such concentration profiles are also present in the case of turbulent wakes but show a finite extension. The sphere shadow is followed by a region around the axis of symmetry where the concentration is higher than the average. It originates from a resonant centrifugal expulsion of particles from shed vortices. The consequence of this concentration mechanism on monodisperse inter-particle collision...

  3. The dynamical crossover in attractive colloidal systems

    Energy Technology Data Exchange (ETDEWEB)

    Mallamace, Francesco [Dipartimento di Fisica e Scienze della Terra, Università di Messina and CNISM, I-98168 Messina (Italy); Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Corsaro, Carmelo [Dipartimento di Fisica e Scienze della Terra, Università di Messina and CNISM, I-98168 Messina (Italy); Stanley, H. Eugene [Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215 (United States); Mallamace, Domenico [Dipartimento di Scienze dell’Ambiente, della Sicurezza, del Territorio, degli Alimenti e della Salute, Università di Messina, I-98166 Messina (Italy); Chen, Sow-Hsin [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2013-12-07

    We study the dynamical arrest in an adhesive hard-sphere colloidal system. We examine a micellar suspension of the Pluronic-L64 surfactant in the temperature (T) and volume fraction (ϕ) phase diagram. According to mode-coupling theory (MCT), this system is characterized by a cusp-like singularity and two glassy phases: an attractive glass (AG) phase and a repulsive glass (RG) phase. The T − ϕ phase diagram of this system as confirmed by a previous series of scattering data also exhibits a Percolation Threshold (PT) line, a reentrant behavior (AG-liquid-RG), and a glass-to-glass transition. The AG phase can be generated out of the liquid phase by using T and ϕ as control parameters. We utilize viscosity and nuclear magnetic resonance (NMR) techniques. NMR data confirm all the characteristic properties of the colloidal system phase diagram and give evidence of the onset of a fractal-like percolating structure at a precise threshold. The MCT scaling laws used to study the shear viscosity as a function of ϕ and T show in both cases a fragile-to-strong liquid glass-forming dynamic crossover (FSC) located near the percolation threshold where the clustering process is fully developed. These results suggest a larger thermodynamic generality for this phenomenon, which is usually studied only as a function of the temperature. We also find that the critical values of the control parameters, coincident with the PT line, define the locus of the FSC. In the region between the FSC and the glass transition lines the system dynamics are dominated by clustering effects. We thus demonstrate that it is possible, using the conceptual framework provided by extended mode-coupling theory, to describe the way a system approaches dynamic arrest, taking into account both cage and hopping effects.

  4. 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.

  5. Phase diagram of aggregation of oppositely charged colloids in salty water.

    Science.gov (United States)

    Zhang, R; Shklovskii, B I

    2004-02-01

    Aggregation of two oppositely charged colloids in salty water is studied. We focus on the role of Coulomb interaction in strongly asymmetric systems in which the charge and size of one colloid is much larger than the other one. In the solution, each large colloid (macroion) attracts a certain number of oppositely charged small colloids (Z-ion) to form a complex. If the concentration ratio of the two colloids is such that complexes are not strongly charged, they condense in a macroscopic aggregate. As a result, the phase diagram in a plane of concentrations of two colloids consists of an aggregation domain sandwiched between two domains of stable solutions of complexes. The aggregation domain has a central part of total aggregation and two wings corresponding to partial aggregation. A quantitative theory of the phase diagram in the presence of monovalent salt is developed. It is shown that as the Debye-Hückel screening radius r(s) decreases, the aggregation domain grows, but the relative size of the partial aggregation domains becomes much smaller. As an important application of the theory, we consider solutions of long double-helix DNA with strongly charged positive spheres (artificial chromatin). We also consider implications of our theory for in vitro experiments with the natural chromatin. Finally, the effect of different shapes of macroions on the phase diagram is discussed.

  6. Capillary-force-induced formation of luminescent polystyrene/(rare-earth-doped nanoparticle) hybrid hollow spheres.

    Science.gov (United States)

    Chen, Min; Xie, Lin; Li, Fuyou; Zhou, Shuxue; Wu, Limin

    2010-10-01

    This paper presents a "one-pot" procedure to synthesize polystyrene/(rare-earth-doped nanoparticles) (PS/REDNPs) hybrid hollow spheres via the in situ diffusion of organic core into inorganic shell under strong capillary force. In this approach, when carboxyl-capped PS colloids were deposited by different REDNPs in aqueous medium, such as LaF3:Eu3+, LaF3:Ce3+-Tb3+, and YVO4:Dy3+, PS/REDNPs inorganic-organic hybrid hollow spheres could be directly obtained via the in situ diffusion of core PS chains into the voids between rare-earth-doped nanoparticles through the strong capillary force. Not only is the synthetic procedure versatile and very simple, but also the obtained hybrid hollow spheres are hydrophilic and luminescent and could be directly used in chemical and biological fields.

  7. Colloids in Acute Burn Resuscitation.

    Science.gov (United States)

    Cartotto, Robert; Greenhalgh, David

    2016-10-01

    Colloids have been used in varying capacities throughout the history of formula-based burn resuscitation. There is sound experimental evidence that demonstrates colloids' ability to improve intravascular colloid osmotic pressure, expand intravascular volume, reduce resuscitation requirements, and limit edema in unburned tissue following a major burn. Fresh frozen plasma appears to be a useful and effective immediate burn resuscitation fluid but its benefits must be weighed against its costs, and risks of viral transmission and acute lung injury. Albumin, in contrast, is less expensive and safer and has demonstrated ability to reduce resuscitation requirements and possibly limit edema-related morbidity. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. Microfluidic Control Using Colloidal Devices

    Science.gov (United States)

    Terray, Alex; Oakey, John; Marr, David W. M.

    2002-06-01

    By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.

  9. Packing of crystalline structures of binary hard spheres: an analytical approach and application to amorphization.

    Science.gov (United States)

    Brouwers, H J H

    2007-10-01

    The geometrical stability of the three lattices of the cubic crystal system, viz. face-centered cubic (fcc), body-centered cubic (bcc), and simple cubic (sc), consisting of bimodal discrete hard spheres, and the transition to amorphous packing is studied. First, the random close packing (rcp) fraction of binary mixtures of amorphously packed spheres is recapitulated. Next, the packing of a binary mixture of hard spheres in randomly disordered cubic structures is analyzed, resulting in original analytical expressions for the unit cell volume and the packing fraction, and which are also valid for the other five crystal systems. The bimodal fcc lattice parameter appears to be in close agreement with empirical hard sphere data from literature, and this parameter could be used to distinguish the size mismatch effect from all other effects in distorted binary lattices of materials. Here, as a first model application, bimodal amorphous and crystalline fcc/bcc packing fractions are combined, yielding the optimum packing configuration, which depends on mixture composition and diameter ratio only. Maps of the closest packing mode are established and applied to colloidal mixtures of polydisperse spheres and to binary alloys of bcc, fcc, and hcp metals. The extensive comparison between the analytical expressions derived here and the published numerical and empirical data yields good agreement. Hence, it is seen that basic space-filling theories on "simple" noninteracting hard spheres are a valuable tool for the study of crystalline materials.

  10. Packing of crystalline structures of binary hard spheres: An analytical approach and application to amorphization

    Science.gov (United States)

    Brouwers, H. J. H.

    2007-10-01

    The geometrical stability of the three lattices of the cubic crystal system, viz. face-centered cubic (fcc), body-centered cubic (bcc), and simple cubic (sc), consisting of bimodal discrete hard spheres, and the transition to amorphous packing is studied. First, the random close packing (rcp) fraction of binary mixtures of amorphously packed spheres is recapitulated. Next, the packing of a binary mixture of hard spheres in randomly disordered cubic structures is analyzed, resulting in original analytical expressions for the unit cell volume and the packing fraction, and which are also valid for the other five crystal systems. The bimodal fcc lattice parameter appears to be in close agreement with empirical hard sphere data from literature, and this parameter could be used to distinguish the size mismatch effect from all other effects in distorted binary lattices of materials. Here, as a first model application, bimodal amorphous and crystalline fcc/bcc packing fractions are combined, yielding the optimum packing configuration, which depends on mixture composition and diameter ratio only. Maps of the closest packing mode are established and applied to colloidal mixtures of polydisperse spheres and to binary alloys of bcc, fcc, and hcp metals. The extensive comparison between the analytical expressions derived here and the published numerical and empirical data yields good agreement. Hence, it is seen that basic space-filling theories on “simple” noninteracting hard spheres are a valuable tool for the study of crystalline materials.

  11. Mesoporous carbon spheres with controlled porosity for high-performance lithium-sulfur batteries

    Science.gov (United States)

    Wang, Dexian; Fu, Aiping; Li, Hongliang; Wang, Yiqian; Guo, Peizhi; Liu, Jingquan; Zhao, Xiu Song

    2015-07-01

    Mesoporous carbon (MC) spheres with hierarchical pores, controlled pore volume and high specific surface areas have been prepared by a mass-producible spray drying assisted template method using sodium alginate as carbon precursor and commercial colloidal silica particles as hard template. The resulting MC spheres, possessing hierarchical pores in the range of 3-30 nm, are employed as conductive matrices for the preparation of cathode materials for lithium-sulfur batteries. A high pressure induced one-step impregnation of elemental sulfur into the pore of the MC spheres has been exploited. The electrochemical performances of sulfur-impregnated MC spheres (S-MC) derived from MC spheres with different pore volume and specific surface area but with the same sulfur loading ratio of 60 wt% (S-MC-X-60) have been investigated in details. The S-MC-4-60 composite cathode material displayed a high initial discharge capacity of 1388 mAhg-1 and a good cycling stability of 857 mAhg-1 after 100 cycles at 0.2C, and shows also excellent rate capability of 864 mAhg-1 at 2C. More importantly, the sulfur loading content in MC-4 spheres can reach as high as 80%, and it still can deliver a capacity of 569 mAhg-1 after 100 cycles at 0.2C.

  12. Efficient linear programming algorithm to generate the densest lattice sphere packings.

    Science.gov (United States)

    Marcotte, Étienne; Torquato, Salvatore

    2013-06-01

    Finding the densest sphere packing in d-dimensional Euclidean space R(d) is an outstanding fundamental problem with relevance in many fields, including the ground states of molecular systems, colloidal crystal structures, coding theory, discrete geometry, number theory, and biological systems. Numerically generating the densest sphere packings becomes very challenging in high dimensions due to an exponentially increasing number of possible sphere contacts and sphere configurations, even for the restricted problem of finding the densest lattice sphere packings. In this paper we apply the Torquato-Jiao packing algorithm, which is a method based on solving a sequence of linear programs, to robustly reproduce the densest known lattice sphere packings for dimensions 2 through 19. We show that the TJ algorithm is appreciably more efficient at solving these problems than previously published methods. Indeed, in some dimensions, the former procedure can be as much as three orders of magnitude faster at finding the optimal solutions than earlier ones. We also study the suboptimal local density-maxima solutions (inherent structures or "extreme" lattices) to gain insight about the nature of the topography of the "density" landscape.

  13. Colloids in Paints Colloids and Interface Science, Volume 6

    CERN Document Server

    Tadros, Tharwat F

    2011-01-01

    The first modern approach to relate fundamental research to the applied science of colloids, this series bridges academic research and practical applications, thus providing the information vital to both. Written by the very best scientists in their respective disciplines, this volume describes the role of colloids in paints, highlighting the importance of fundamental research in industrial applications.For surface, polymer and physicochemists, materials scientists, and chemical engineers.

  14. Are All Colloids Same? How to Select the Right Colloid?

    Directory of Open Access Journals (Sweden)

    Sukanya Mitra

    2009-01-01

    Full Text Available The administration of intravenous fluids is one of the most common and universal interventions in medicine. Colloids are an alternative to the frequently used crystalloids, with highly variable use depending on a myriad of clinical variables. A colloid is defined as a high molecular weight (MW substance that largely remains in the intravas-eular compartment, thereby generating an oncotic pressure. Colloids are considered to have a greater intravaseular persistence when compared to crystalloids. All colloids, however, are clearly not the same. Differences in the physi-cochemical properties, pharmacokinetics and safety profile exist amongst various colloids. This review explores the different types of colloids, with their properties and usefulness as well as adverse effects. While all the available colloids are reviewed briefly (e.g., albumin, gelatin, dextran with respect to their pharmacology, indications, advan-tages and disadvantages, particular emphasis is laid on the hydroxyethyl starches (HES because of their rising prominence. It is shown that HES differ widely in their physicochemical and pharmacokinetic properties, composition, usefulness, and especially in their adverse effect profiles. The third generation HES (tetrastarches, in particular, seem to offer a unique combination of safety and efficacy. Several issues related to this are discussed in detail. This review of the available clinical data demonstrates that HES should not be regarded as one homogenous group, and data for one product should not be automatically extrapolated to another. Thus, among the synthetic colloids, the tetrastarches appear to offer the best currently available compromise between efficacy, safety profile, and cost. They also appear to be the best suited for use in the intensive care setting. Finally, balanced (rather than saline-based HES solutions appear promising as a plasma-adapted volume replacement strategy and may further refine the ongoing quest of

  15. Staged phase separation in the I-I-N tri-phase region of platelet-sphere mixtures.

    Science.gov (United States)

    Chen, Mingfeng; He, Min; Lin, Pengcheng; Chen, Ying; Cheng, Zhengdong

    2017-06-28

    Mixtures of colloids with different sizes or shapes are ubiquitous in nature and extensively applied in industries. Phase transition pathways and kinetics in this model system should be investigated because of the difficulty in observing tri-phase coexistence in colloidal platelet-sphere mixtures. Similar to the polymer-sphere mixtures, the phase transition pathway has three main categories. Analytical results show a staged phase transition process in which the mixture first separates into one or two metastable phases, then further separates, and subsequently reaches tri-phase equilibrium. Unique to our system, and different from the gas-liquid-crystal coexistence in colloid-polymer mixtures, the platelet-sphere mixture reached a gas-liquid-liquid crystal (nematic) coexistence. Thus, the different phases are easy to distinguish using the birefringence of the liquid crystals. In addition, the volume fraction of the liquid crystal formation in the ZrP platelet suspensions is much lower than for the crystal formation in hard spheres.

  16. Large-scale assembly of colloidal particles

    Science.gov (United States)

    Yang, Hongta

    increase of the effective refractive index of the diffractive medium, resulting in the red-shift of the optical stop bands. The wavelength shift is linearly proportional to the vapor partial pressure for a spectrum of vapors. Optical simulation and theoretical prediction based on Kelvin equation suggest that a liquid film is formed on the walls of the macropores during vapor condensation. The third topic describes introducing doctor blade coating fabricated large area and low cost macroporous films for thermochromic smart windows, which are useful for energy control in glazed buildings. The fabricated macroporous polymer films exhibit brilliant colors and are capable of reflecting solar radiation when in-situ heated, and become transparent as cavities are filled with a solvent which has the same refractive index as that of the polymer when cooled to building temperature. The fourth topic reports the roll-to roll fabricated excellent water-repelling and self-cleaning macroporous polymer films. The size of the voids can be easily controlled by tuning the duration of an oxygen reactive-ion etching process prior to the removal of the templating silica spheres from silica colloidal-polymer composites. After surface functionalization with fluorosilane, superhydrophobic surface with large apparent water contact angle and small sliding angle can be obtained. The self-cleaning functionality can be achieved on superhydrophobic macroporous coatings by preventing bacterial contamination is further demonstrated. The fifth topic presented is that the template macroporous polymer films with interconnected voids and uniform interconnecting nanopores can be directly used as filtration membranes to achieve size-exclusive separation of particles. The results also demonstrate that more than 85% of small sized particles are recovered after filtration. The results also demonstrate that Escherichia coli can be filtrated by the from macroporous polymer films aqueous solution.

  17. Structure, dynamics, and rheology of concentrated dispersions of poly(ethylene glycol)-grafted colloids

    OpenAIRE

    Zackrisson, Malin; Stradner, Anna; Schurtenberger, Peter; Bergenholtz, Johan

    2006-01-01

    A comprehensive experimental study of the dynamics and rheology of concentrated aqueous dispersions of poly(ethylene glycol)-grafted colloidal spheres is reported. The study focuses on good solvent conditions, for which excluded-volume interactions dominate. At high concentrations a glass transition is evident from the nondecaying component of the intensity correlation function measured with three-dimensional dynamic light scattering. Results for the linear viscoelastic and steady shear rheol...

  18. Encapsulation of Polymer Colloids in a Sol-Gel Matrix. Direct-Writing of Coassembling Organic-Inorganic Hybrid Photonic Crystals.

    Science.gov (United States)

    Mikosch, Annabel; Kuehne, Alexander J C

    2016-03-22

    The spontaneous self-assembly of polymer colloids into ordered arrangements provides a facile strategy for the creation of photonic crystals. However, these structures often suffer from defects and insufficient cohesion, which result in flaking and delamination from the substrate. A coassembly process has been developed for convective assembly, resulting in large-area encapsulated colloidal crystals. However, to generate patterns or discrete deposits in designated places, convective assembly is not suitable. Here we experimentally develop conditions for direct-writing of coassembling monodisperse dye-doped polystyrene particles with a sol-gel precursor to form solid encapsulated photonic crystals. In a simple procedure the colloids are formulated in a sol-gel precursor solution, drop-cast on a flat substrate, and dried. We here establish the optimal parameters to form reproducible highly ordered photonic crystals with good optical performance. The obtained photonic crystals interact with light in the visible spectrum with a narrow optical stop-gap.

  19. Theory of repulsive charged colloids in slit-pores

    Science.gov (United States)

    Gallardo, Alberto; Grandner, Stefan; Almarza, Noé G.; Klapp, Sabine H. L.

    2012-07-01

    Using classical density functional theory (DFT) we analyze the structure of the density profiles and solvation pressures of negatively charged colloids confined in slit pores. The considered model, which was already successfully employed to study a real colloidal (silica) suspension [S. H. L. Klapp et al., Phys. Rev. Lett. 100, 118303 (2008), 10.1103/PhysRevLett.100.118303], involves only the macroions which interact via the effective Derjaguin-Landau-Verwey-Overbeek (DLVO) potential supplemented by a hard core interaction. The solvent enters implicitly via the screening length of the DLVO interaction. The free energy functional describing the colloidal suspension consists of a hard sphere contribution obtained from fundamental measure theory and a long range contribution which is treated using two types of approximations. One of them is the mean field approximation (MFA) and the remaining is based on Rosenfeld's perturbative method for constructing the Helmholtz energy functional. These theoretical calculations are carried out at different bulk densities and wall separations to compare finally to grand canonical Monte Carlo simulations. We also consider the impact of charged walls. Our results show that the perturbative DFT method yields generally qualitatively consistent and, for some systems, also quantitatively reliable results. In MFA, on the other hand, the neglect of charge-induced correlations leads to a breakdown of this approach in a broad range of densities.

  20. Sagging of evaporating droplets of colloidal suspensions on inclined substrates.

    Science.gov (United States)

    Espín, Leonardo; Kumar, Satish

    2014-10-14

    A droplet of a colloidal suspension placed on an inclined substrate may sag under the action of gravity. Solvent evaporation raises the concentration of the colloidal particles, and the resulting viscosity changes may influence the sag of the droplet. To investigate this phenomenon, we have developed a mathematical model for perfectly wetting droplets based on lubrication theory and the rapid-vertical-diffusion approximation. Precursor films are assumed to be present, the colloidal particles are taken to be hard spheres, and particle and liquid dynamics are coupled through a concentration-dependent viscosity and diffusivity. Evaporation is assumed to be limited by how rapidly solvent molecules can transfer from the liquid to the vapor phase. The resulting one-dimensional system of nonlinear partial differential equations describing the evolution of the droplet height and particle concentration is solved numerically for a range of initial particle concentrations and substrate temperatures. The solutions reveal that the interaction between evaporation and non-Newtonian suspension rheology gives rise to several distinct regimes of droplet shapes and particle concentration distributions. The results provide insight into how evaporation and suspension rheology can be tuned to minimize sagging as well as the well-known coffee-ring effect, an outcome which is important for industrial coating processes.

  1. Acoustically trapped colloidal crystals that are reconfigurable in real time.

    Science.gov (United States)

    Caleap, Mihai; Drinkwater, Bruce W

    2014-04-29

    Photonic and phononic crystals are metamaterials with repeating unit cells that result in internal resonances leading to a range of wave guiding and filtering properties and are opening up new applications such as hyperlenses and superabsorbers. Here we show the first, to our knowledge, 3D colloidal phononic crystal that is reconfigurable in real time and demonstrate its ability to rapidly alter its frequency filtering characteristics. Our reconfigurable material is assembled from microspheres in aqueous solution, trapped with acoustic radiation forces. The acoustic radiation force is governed by an energy landscape, determined by an applied high-amplitude acoustic standing wave field, in which particles move swiftly to energy minima. This creates a colloidal crystal of several milliliters in volume with spheres arranged in an orthorhombic lattice in which the acoustic wavelength is used to control the lattice spacing. Transmission acoustic spectroscopy shows that the new colloidal crystal behaves as a phononic metamaterial and exhibits clear band-pass and band-stop frequencies which are adjusted in real time.

  2. Surface-modified silica colloidal crystals: nanoporous films and membranes with controlled ionic and molecular transport.

    Science.gov (United States)

    Zharov, Ilya; Khabibullin, Amir

    2014-02-18

    Nanoporous membranes are important for the study of the transport of small molecules and macromolecules through confined spaces and in applications ranging from separation of biomacromolecules and pharmaceuticals to sensing and controlled release of drugs. For many of these applications, chemists need to gate the ionic and molecular flux through the nanopores, which in turn depends on the ability to control the nanopore geometry and surface chemistry. Most commonly used nanoporous membrane materials are based on polymers. However, the nanostructure of polymeric membranes is not well-defined, and their surface is hard to modify. Inorganic nanoporous materials are attractive alternatives for polymers in the preparation of nanoporous membranes. In this Account, we describe the preparation and surface modification of inorganic nanoporous films and membranes self-assembled from silica colloidal spheres. These spheres form colloidal crystals with close-packed face centered cubic lattices upon vertical deposition from colloidal solutions. Silica colloidal crystals contain ordered arrays of interconnected three dimensional voids, which function as nanopores. We can prepare silica colloidal crystals as supported thin films on various flat solid surfaces or obtain free-standing silica colloidal membranes by sintering the colloidal crystals above 1000 °C. Unmodified silica colloidal membranes are capable of size-selective separation of macromolecules, and we can surface-modify them in a well-defined and controlled manner with small molecules and polymers. For the surface modification with small molecules, we use silanol chemistry. We grow polymer brushes with narrow molecular weight distribution and controlled length on the colloidal nanopore surface using atom transfer radical polymerization or ring-opening polymerization. We can control the flux in the resulting surface-modified nanoporous films and membranes by pH and ionic strength, temperature, light, and small molecule

  3. Colloidal gels: Clay goes patchy

    Science.gov (United States)

    Kegel, Willem K.; Lekkerkerker, Henk N. W.

    2011-01-01

    Empty liquids and equilibrium gels have so far been only theoretical possibilities, predicted for colloids with patchy interactions. But evidence of both has now been found in Laponite, a widely studied clay.

  4. Active colloids in complex fluids

    CERN Document Server

    Patteson, Alison E; Arratia, Paulo E

    2016-01-01

    We review recent work on active colloids or swimmers, such as self-propelled microorganisms, phoretic colloidal particles, and artificial micro-robotic systems, moving in fluid-like environments. These environments can be water-like and Newtonian but can frequently contain macromolecules, flexible polymers, soft cells, or hard particles, which impart complex, nonlinear rheological features to the fluid. While significant progress has been made on understanding how active colloids move and interact in Newtonian fluids, little is known on how active colloids behave in complex and non-Newtonian fluids. An emerging literature is starting to show how fluid rheology can dramatically change the gaits and speeds of individual swimmers. Simultaneously, a moving swimmer induces time dependent, three dimensional fluid flows, that can modify the medium (fluid) rheological properties. This two-way, non-linear coupling at microscopic scales has profound implications at meso- and macro-scales: steady state suspension proper...

  5. Physical ageing of the contact line on colloidal particles at liquid interfaces.

    Science.gov (United States)

    Kaz, David M; McGorty, Ryan; Mani, Madhav; Brenner, Michael P; Manoharan, Vinothan N

    2011-12-04

    Young's law predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle. This has been used to explain why colloids often bind to liquid interfaces, and has been exploited in emulsification, water purification, mineral recovery, encapsulation and the making of nanostructured materials. However, little is known about the dynamics of binding. Here we show that the adsorption of polystyrene microspheres to a water/oil interface is characterized by a sudden breach and an unexpectedly slow relaxation. The relaxation appears logarithmic in time, indicating that complete equilibration may take months. Surprisingly, viscous dissipation appears to play little role. Instead, the observed dynamics, which bear strong resemblance to ageing in glassy systems, agree well with a model describing activated hopping of the contact line over nanoscale surface heterogeneities. These results may provide clues to longstanding questions on colloidal interactions at an interface.

  6. Sedimentation equilibria of ferrofluids: II. Experimental osmotic equations of state of magnetite colloids.

    Science.gov (United States)

    Luigjes, Bob; Thies-Weesie, Dominique M E; Erné, Ben H; Philipse, Albert P

    2012-06-20

    The first experimental osmotic equation of state is reported for well-defined magnetic colloids that interact via a dipolar hard-sphere potential. The osmotic pressures are determined from the sedimentation equilibrium concentration profiles in ultrathin capillaries using a low-velocity analytical centrifuge, which is the subject of the accompanying paper I. The pressures of the magnetic colloids, measured accurately to values as low as a few pascals, obey Van 't Hoff's law at low concentrations, whereas at increasing colloid densities non-ideality appears in the form of a negative second virial coefficient. This virial coefficient corresponds to a dipolar coupling constant that agrees with the coupling constant obtained via independent magnetization measurements. The coupling constant manifests an attractive potential of mean force that is significant but yet not quite strong enough to induce dipolar chain formation. Our results disprove van der Waals-like phase behavior of dipolar particles for reasons that are explained.

  7. 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

  8. Unveiling small sphere's scattering behavior

    CERN Document Server

    Tzarouchis, Dimitrios C; Sihvola, Ari

    2016-01-01

    A classical way for exploring the scattering behavior of a small sphere is to approximate Mie coefficients with a Taylor series expansion. This ansatz delivered a plethora of insightful results, mostly for small spheres supporting electric localized plasmonic resonances. However, many scattering aspects are still uncharted, especially for the case of magnetic resonances. Here, an alternative system ansatz is proposed based on the Pad\\'e approximants for the Mie coefficients. The extracted results reveal new aspects, such as the existence of a self-regulating radiative damping mechanism for the first magnetic resonance. Hence, a systematic way of exploring the scattering behavior is introduced, sharpening our understanding about sphere's scattering behavior and its emergent functionalities.

  9. Public Sphere as Digital Assemblage

    DEFF Research Database (Denmark)

    Salovaara-Moring, Inka

    the 1990s onwards digitalization brought concepts of network and complexity into the theoretical discourse. This relational turn changed the social ontology of the public sphere into a dynamic and complex system, erasing the division between the fields of reality (the world), representation (discourse...... theories. Drawing from Deleuze & Guattari (1987), Bennett (2010), and Latour (2004) in order to imagine post-human assemblages of public sphere, this paper argues for a relational ontology that emphasizes the complex interactions of political assemblages. Empirically, it draws from the author’s studies......Normative theories of public sphere have struggled with the topic of materiality. The historical narrative of the ‘public sphere’ situated the phenomenon in specific spaces, where practices (public deliberation) and language (discourse) constructed political agencies, and further publics. From...

  10. Matrix dynamics of fuzzy spheres

    CERN Document Server

    Jatkar, D P; Wadia, S R; Yogendran, K P; Jatkar, Dileep P.; Mandal, Gautam; Wadia, Spenta R.

    2002-01-01

    We study the dynamics of fuzzy two-spheres in a matrix model which represents string theory in the presence of RR flux. We analyze the stability of known static solutions of such a theory which contain commuting matrices and SU(2) representations. We find that irreducible as well as reducible representations are stable. Since the latter are of higher energy, this stability poses a puzzle. We resolve this puzzle by noting that reducible representations have marginal directions corresponding to non-spherical deformations. We obtain new static solutions by turning on these marginal deformations. These solutions now have instability or tachyonic directions. We discuss condensation of these tachyons which correspond to classical trajectories interpolating from multiple, small fuzzy spheres to a single, large sphere. We briefly discuss spatially independent configurations of a D3/D5 system described by the same matrix model which now possesses a supergravity dual.

  11. Hollow titania spheres with movable silica spheres inside.

    Science.gov (United States)

    Zhang, Kai; Zhang, Xuehai; Chen, Haitao; Chen, Xin; Zheng, Linli; Zhang, Junhu; Yang, Bai

    2004-12-21

    We demonstrate a flexible method for preparing hollow TiO2 nanospheres with movable silica nanoparticles inside (HTNMSNs). In this method, we used monodisperse silica--polystyrene core--shell nanospheres (SiO2-PS-CSNs) sulfonated as templates and prepared the composite shell consisting of TiO2 and sulfonated polystyrene (SPS) through adsorbing or depositing tetrabutyl titanate gel into the SPS shell. Finally the HTNMSNs were obtained after removal of all polymers in the composite nanospheres by dissolution or calcinations. We investigated the dependence of the morphologies of HTNMSNs on the thickness of PS shells and the size of SiO2 cores and prepared rare earth doped HTNMSNs by a sol-gel process.

  12. Monodispersed Zinc Oxide Nanoparticle-Dye Dyads and Triads

    Energy Technology Data Exchange (ETDEWEB)

    Gladfelter, Wayne L. [Univ. of Minnesota, Minneapolis, MN (United States); Blank, David A. [Univ. of Minnesota, Minneapolis, MN (United States); Mann, Kent R. [Univ. of Minnesota, Minneapolis, MN (United States)

    2017-06-22

    events at a fundamental level. This was combined with the synthesis of a broad range of sensitizers that provide systematic variation of the energetics, excited state dynamics, structure and interfacial bonding. The key is that the monodisperse nature and high dispersibility of the ZnO NCs made these experiments reproducible; in essence, the measurements were on discrete molecular species rather than on the complicated mixtures that resulted from the typical fabrication of functional photovoltaic cells. The monodispersed nature of the NCs also allowed the use of quantum confinement to investigate the role of donor/acceptor energetic alignment in chemically identical systems. The results added significantly to our basic understanding of energy and charge transfer events at molecule-semiconductor interfaces and will help the R&D community realize zinc oxide's full potential in solar cell applications.

  13. Frequency domain photon migration measurements of dense monodisperse charged lattices and analysis using solutions of Ornstein Zernike equations.

    Science.gov (United States)

    Dali, Sarabjyot S; Sevick-Muraca, Eva M

    2012-11-15

    Isotropic scattering coefficient measurements were made of monodisperse polystyrene lattices of two different diameters of 144 nm and 223 nm and at volume fractions ranging from 0.15 to 0.22, using frequency domain photon migration measurements at wavelengths of 660, 685, 785 and 828 nm. The isotropic scattering coefficient measurements were shown to be sensitive to the changing ionic strength (0.5-4 mM, NaCl equiv.) of the dispersions exhibiting hindered scattering owing to structure at the lowest ionic strength values. Monte Carlo simulations and numerical solution of the Ornstein Zernike equations were used to compute isotropic scattering coefficients for comparison to measured values. The interaction potential was modeled as a hard sphere Yukawa potential and the Hypernetted Chain closure was used to solve the OZ equation. Effective particle charges were found after renormalization of the bare particle charge and used to predict the isotropic scattering coefficient. The model data were found to follow similar trends as experimental measurements. The refractive index of the particles has found to be an important factor for predicting experimental isotropic scattering coefficient values. Published by Elsevier Inc.

  14. Efficient thermolysis route to monodisperse Cu₂ZnSnS₄ nanocrystals with controlled shape and structure

    National Research Council Canada - National Science Library

    Zhang, Xiaoyan; Guo, Guobiao; Ji, Cheng; Huang, Kai; Zha, Chenyang; Wang, Yifeng; Shen, Liming; Gupta, Arunava; Bao, Ningzhong

    2014-01-01

    Monodisperse Cu2ZnSnS4 (CZTS) nanocrystals with tunable shape, crystalline phase, and composition are synthesized by efficient thermolysis of a single source precursor of mixed metal-oleate complexes in hot organic solvents...

  15. Cr/alpha-Cr2O3 monodispersed spherical core-shell particles based solar absorbers

    CSIR Research Space (South Africa)

    Khamlich, S

    2011-07-01

    Full Text Available Monodispersed spherical core-shell particles of Cr/alpha-Cr2O3 cermet ACG coatings investigated within this contribution could be successfully employed in thermal converters. Their selectivity depends on their chemical, physical and structural...

  16. Troubleshooting vSphere storage

    CERN Document Server

    Preston, Mike

    2013-01-01

    This is a step-by-step example-oriented tutorial aimed at showing the reader how to troubleshoot a variety of vSphere storage problems, and providing the reader with solutions that can be completed with minimal effort and time in order to limit damage to work.If you are a vSphere administrator, this is the book for you. This book will provide you with 'need to know' information about the various storage transports that ESXi utilizes, the tools and techniques we can use to identify problems, and the fundamental knowledge and steps to take to troubleshoot storage-related issues. Prior knowledge

  17. Adhesion of bacterial pathogens to soil colloidal particles: influences of cell type, natural organic matter, and solution chemistry.

    Science.gov (United States)

    Zhao, Wenqiang; Walker, Sharon L; Huang, Qiaoyun; Cai, Peng

    2014-04-15

    Bacterial adhesion to granular soil particles is well studied; however, pathogen interactions with naturally occurring colloidal particles (organic matter (NOM), and solution chemistry. Specifically, batch adhesion experiments were conducted using NOM-present, NOM-stripped soil colloids, Streptococcus suis SC05 and Escherichia coli WH09 over a wide range of solution pH (4.0-9.0) and ionic strength (IS, 1-100 mM KCl). Cell characterization techniques, Freundlich isotherm, and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory (sphere-sphere model) were utilized to quantitatively determine the interactions between cells and colloids. The adhesion coefficients (Kf) of S. suis SC05 to NOM-present and NOM-stripped soil colloids were significantly higher than E. coli WH09, respectively. Similarly, Kf values of S. suis SC05 and E. coli WH09 adhesion to NOM-stripped soil colloids were greater than those colloids with NOM-present, respectively, suggesting NOM inhibits bacterial adhesion. Cell adhesion to soil colloids declined with increasing pH and enhanced with rising IS (1-50 mM). Interaction energy calculations indicate these adhesion trends can be explained by DLVO-type forces, with S. suis SC05 and E. coli WH09 being weakly adhered in shallow secondary energy minima via polymer bridging and charge heterogeneity. S. suis SC05 adhesion decreased at higher IS 100 mM, which is attributed to the change of hydrophobic effect and steric repulsion resulted from the greater presence of extracellular polymeric substances (EPS) on S. suis SC05 surface as compared to E. coli WH09. Hence, pathogen adhesion to the colloidal material is determined by a combination of DLVO, charge heterogeneity, hydrophobic and polymer interactions as a function of solution chemistry.

  18. Density Fluctuations of Hard-Sphere Fluids in Narrow Confinement

    Science.gov (United States)

    Nygârd, Kim; Sarman, Sten; Hyltegren, Kristin; Chodankar, Shirish; Perret, Edith; Buitenhuis, Johan; van der Veen, J. Friso; Kjellander, Roland

    2016-01-01

    Spatial confinement induces microscopic ordering of fluids, which in turn alters many of their dynamic and thermodynamic properties. However, the isothermal compressibility has hitherto been largely overlooked in the literature, despite its obvious connection to the underlying microscopic structure and density fluctuations in confined geometries. Here, we address this issue by probing density profiles and structure factors of hard-sphere fluids in various narrow slits, using x-ray scattering from colloid-filled nanofluidic containers and integral-equation-based statistical mechanics at the level of pair distributions for inhomogeneous fluids. Most importantly, we demonstrate that density fluctuations and isothermal compressibilities in confined fluids can be obtained experimentally from the long-wavelength limit of the structure factor, providing a formally exact and experimentally accessible connection between microscopic structure and macroscopic, thermodynamic properties. Our approach will thus, for example, allow direct experimental verification of theoretically predicted enhanced density fluctuations in liquids near solvophobic interfaces.

  19. Facile and Scalable Synthesis of Monodispersed Spherical Capsules with a Mesoporous Shell

    KAUST Repository

    Qi, Genggeng

    2010-05-11

    Monodispersed HMSs with tunable particle size and shell thickness were successfully synthesized using relatively concentrated polystyrene latex templates and a silica precursor in a weakly basic ethanol/water mixture. The particle size of the capsules can vary from 100 nm to micrometers. These highly engineered monodispersed capsules synthesized by a facile and scalable process may find applications in drug delivery, catalysis, separationm or as biological and chemical microreactors. © 2010 American Chemical Society.

  20. Osmotic compressibility of soft colloidal systems.

    Science.gov (United States)

    Tan, Beng H; Tam, Kam C; Lam, Yee C; Tan, Chee B

    2005-05-10

    A turbidimetric analysis of particle interaction of model pH-responsive microgel systems consisting of methacrylic acid-ethyl acrylate cross-linked with diallyl phthalate in colloidal suspensions is described. The structure factor at zero scattering angle, S(0), can be determined with good precision for wavelengths greater than 500 nm, and it measures the dispersion's resistance to particle compression. The structure factor of microgels at various cross-linked densities and ionic strengths falls onto a master curve when plotted against the effective volume fraction, phi(eff) = kc, which clearly suggests that particle interaction potential and osmotic compressibility is a function of effective volume fraction. In addition, the deviation of the structure factor, S(0), of our microgel systems with the structure factor of hard spheres, S(PY)(0), exhibits a maximum at phi(eff) approximately 0.2. Beyond this point the osmotic de-swelling force exceeds the osmotic pressure inside the soft particles resulting in particle shrinkage. Good agreement was obtained when the structural properties of our microgel systems obtained from turbidimetric analysis and rheology measurements were compared. Therefore, a simple turbidimetric analysis of these model pH-responsive microgel systems permits a quantitative evaluation of factors governing particle osmotic compressibility.

  1. Optimization of Optical Absorption of Colloids of SiO2@Au and Fe3O4@Au Nanoparticles with Constraints

    Science.gov (United States)

    Xue, Xiaozheng; Sukhotskiy, Viktor; Furlani, Edward P.

    2016-01-01

    We study the optical response of monodisperse colloids of core-shell plasmonic nanoparticles and introduce a computational approach to optimize absorption for photothermal applications that require dilute colloids of non-interacting particles with a prescribed volume fraction. Since the volume fraction is held constant, the particle concentration is size-dependent. Optimization is achieved by comparing the absorption spectra of colloids as a function of particle size and structure. We demonstrate the approach via application to colloids of core-shell SiO2@Au and Fe3O4@Au nanoparticles with particle sizes that range from 5–100 nm and with the incident wavelength varying from 600–1200 nm. The absorption spectra are predicted using Mie theory and the analysis shows that there is a unique mix of parameters (core radius, shell thickness, wavelength) that maximize absorption, independent of the value of volume fraction. We show that lossy Fe3O4 cores produce a much broader absorption peak with much less sensitivity to variations in particle structure and wavelength than lossless SiO2 cores. This approach can be readily adapted to colloids of nanoparticles with arbitrary materials, shapes and structure using appropriate numerical methods to compute the absorption spectra. As such, it is useful for the rational design of colloids and process variables for a broad range of photothermal applications. PMID:27786279

  2. Periodic jetting and monodisperse jet drops from oblique gas injection

    Science.gov (United States)

    McRae, Oliver; Gaillard, Antoine; Bird, James C.

    2017-07-01

    When air is blown in a straw or tube near an air-liquid interface, typically one of two behaviors is observed: a dimple in the liquid's surface, or a frenzy of sputtering bubbles, waves, and spray. Here we report and characterize an intermediate regime that can develop when a confined air jet enters the interface at an angle. This regime is oscillatory with a distinct characteristic frequency and can develop periodic angled jets that can break up into monodisperse aerosols. The underlying mechanisms responsible for this highly periodic regime are not well understood. Here we flow a continuous stream of gas through a tube near a liquid surface, observing both optically and acoustically the deformation of the liquid-air interface as various parameters are systematically adjusted. We show that the Kelvin-Helmholtz instability is responsible for the inception of waves within a cavity formed by the gas. Inertia, gravity, and capillary forces both shape the cavity and govern the frequency and amplitude of these gas-induced cavity waves. The flapping cavity focuses the waves into a series of periodic jets that can break up into droplets following the Rayleigh-Plateau instability. We present scaling arguments to rationalize the fundamental frequencies driving this system, as well as the conditions that bound the periodic regime. These frequencies and conditions compare well with our experimental results.

  3. Jamming of Monodisperse Cylindrical Grains in Featureless Vertical Channels

    Science.gov (United States)

    Friedl, Nicholas; Baxter, G. William

    2014-03-01

    We study jamming of low aspect-ratio cylindrical Delrin grains falling through a featureless vertical channel under the influence of gravity. These grains have an aspect-ratio less than two (H/D aspirin tablets, 35mm film canisters, poker chips, or coins. Monodisperse grains are allowed to fall under the influence of gravity through a uniform channel of square cross-section where the channel width is greater than the grain size and constant along the length of the channel. No combination of grain heights and diameters is equal to the channel width. Collections of grains sometimes form jams, stable structures in which the grains are supported by the channel walls and not by grains or walls beneath them. The probability of a jam occurring and the jam's strength are influenced by the grain dimensions and channel width. We will present experimental measurements of the jamming probability and jam strength and discuss the relationship of these results to other experiments and theories. Supported by an Undergraduate Research Grant from Penn State Erie, The Behrend College.

  4. Biotemplate synthesis of monodispersed iron phosphate hollow microspheres.

    Science.gov (United States)

    Cao, Feng; Li, Dongxu

    2010-03-01

    Monodispersed iron phosphate hollow microspheres with a high degree of crystallization were prepared through a facile in situ deposition method using rape pollen grains as a biotemplate. The functional group on the surface of the pollen grains could adsorb Fe(3+), which provided the nucleation sites for growth of iron phosphate nanoparticles. After being sintered at 600 degrees C for 10 h, the pollen grains were removed and iron phosphate hollow microspheres were obtained. A scanning electron microscope and x-ray diffraction were applied to characterize the morphology and crystalline structure of the pollen grains, iron phosphate-coated pollen grains and iron phosphate hollow microspheres. Differential scanning calorimetry and thermogravity analyses were performed to investigate the thermal behavior of the iron phosphate-coated pollen grains during the calcinations. Energy dispersive spectroscopy and Fourier transform infrared spectroscopy were utilized to investigate the interaction between the pollen grains and iron phosphate. The effect of the pollen wall on the surface morphology of these iron phosphate hollow microspheres was also proven in this work.

  5. Monodisperse Platinum and Rhodium Nanoparticles as Model Heterogeneous Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Grass, Michael Edward [Univ. of California, Berkeley, CA (United States)

    2008-09-01

    Model heterogeneous catalysts have been synthesized and studied to better understand how the surface structure of noble metal nanoparticles affects catalytic performance. In this project, monodisperse rhodium and platinum nanoparticles of controlled size and shape have been synthesized by solution phase polyol reduction, stabilized by polyvinylpyrrolidone (PVP). Model catalysts have been developed using these nanoparticles by two methods: synthesis of mesoporous silica (SBA-15) in the presence of nanoparticles (nanoparticle encapsulation, NE) to form a composite of metal nanoparticles supported on SBA-15 and by deposition of the particles onto a silicon wafer using Langmuir-Blodgett (LB) monolayer deposition. The particle shapes were analyzed by transmission electron microscopy (TEM) and high resolution TEM (HRTEM) and the sizes were determined by TEM, X-ray diffraction (XRD), and in the case of NE samples, room temperature H2 and CO adsorption isotherms. Catalytic studies were carried out in homebuilt gas-phase reactors. For the nanoparticles supported on SBA-15, the catalysts are in powder form and were studied using the homebuilt systems as plug-flow reactors. In the case of nanoparticles deposited on silicon wafers, the same systems were operated as batch reactors. This dissertation has focused on the synthesis, characterization, and reaction studies of model noble metal heterogeneous catalysts. Careful control of particle size and shape has been accomplished though solution phase synthesis of Pt and Rh nanoparticles in order to elucidate further structure-reactivity relationships in noble metal catalysis.

  6. Facile Synthesis of Monodisperse Gold Nanocrystals Using Virola oleifera

    Science.gov (United States)

    Milaneze, Bárbara A.; Oliveira, Jairo P.; Augusto, Ingrid; Keijok, Wanderson J.; Côrrea, Andressa S.; Ferreira, Débora M.; Nunes, Otalíbio C.; Gonçalves, Rita de Cássia R.; Kitagawa, Rodrigo R.; Celante, Vinícius G.; da Silva, André Romero; Pereira, Ana Claudia H.; Endringer, Denise C.; Schuenck, Ricardo P.; Guimarães, Marco C. C.

    2016-10-01

    The development of new routes and strategies for nanotechnology applications that only employ green synthesis has inspired investigators to devise natural systems. Among these systems, the synthesis of gold nanoparticles using plant extracts has been actively developed as an alternative, efficient, cost-effective, and environmentally safe method for producing nanoparticles, and this approach is also suitable for large-scale synthesis. This study reports reproducible and completely natural gold nanocrystals that were synthesized using Virola oleifera extract. V. oleifera resin is rich in epicatechin, ferulic acid, gallic acid, and flavonoids (i.e., quercetin and eriodictyol). These gold nanoparticles play three roles. First, these nanoparticles exhibit remarkable stability based on their zeta potential. Second, these nanoparticles are functionalized with flavonoids, and third, an efficient, economical, and environmentally friendly mechanism can be employed to produce green nanoparticles with organic compounds on the surface. Our model is capable of reducing the resin of V. oleifera, which creates stability and opens a new avenue for biological applications. This method does not require painstaking conditions or hazardous agents and is a rapid, efficient, and green approach for the fabrication of monodisperse gold nanoparticles.

  7. Ultrasonically Aided Electrospray source for monodisperse, charged nanoparticles

    Science.gov (United States)

    Song, Weidong

    This dissertation presents a new method of producing nearly monodisperse electrospray using charged capillary standing waves. This method, based on the Ultrasonically Aided Electrospraying (UAE) technology concept invented by the author, includes the steps of dispensing a liquid on the top surface of a diaphragm so as to form a liquid film on the surface of the diaphragm, setting the diaphragm into vibration using piezoelectric transducers so as to induce capillary standing waves in the liquid film, applying electric charge to the capillary standing waves so that electrospray is extracted from the crests of the capillary standing waves. Theoretical analysis on the formation of charged particles from charged capillary standing waves at critically stable condition is performed. An experimental UAE system is designed, built, and tested and the performance of this new technology concept is assessed. Experimental results validate the capabilities of the UAE concept. The method has several applications including electric space propulsion, nano particulate technologies, nanoparticle spray coating and painting techniques, semiconductor fabrication and biomedical processes. Two example applications in electric space propulsion and nanoparticle spray coating are introduced.

  8. Spark Ignition of Monodisperse Fuel Sprays. Ph.D. Thesis

    Science.gov (United States)

    Danis, Allen M.; Cernansky, Nicholas P.; Namer, Izak

    1987-01-01

    A study of spark ignition energy requirements was conducted with a monodisperse spray system allowing independent control of droplet size, equivalent ratio, and fuel type. Minimum ignition energies were measured for n-heptane and methanol sprays characterized at the spark gap in terms of droplet diameter, equivalence ratio (number density) and extent of prevaporization. In addition to sprays, minimum ignition energies were measured for completely prevaporized mixtures of the same fuels over a range of equivalence ratios to provide data at the lower limit of droplet size. Results showed that spray ignition was enhanced with decreasing droplet size and increasing equivalence ratio over the ranges of the parameters studied. By comparing spray and prevaporized ignition results, the existence of an optimum droplet size for ignition was indicated for both fuels. Fuel volatility was seen to be a critical factor in spray ignition. The spray ignition results were analyzed using two different empirical ignition models for quiescent mixtures. Both models accurately predicted the experimental ignition energies for the majority of the spray conditions. Spray ignition was observed to be probabilistic in nature, and ignition was quantified in terms of an ignition frequency for a given spark energy. A model was developed to predict ignition frequencies based on the variation in spark energy and equivalence ratio in the spark gap. The resulting ignition frequency simulations were nearly identical to the experimentally observed values.

  9. Biotemplate synthesis of monodispersed iron phosphate hollow microspheres

    Energy Technology Data Exchange (ETDEWEB)

    Cao Feng; Li Dongxu, E-mail: dongxuli@njut.edu.c [College of Materials Science and Engineering, Nanjing University of Technology, Jiangsu Nanjing 210009 (China)

    2010-03-15

    Monodispersed iron phosphate hollow microspheres with a high degree of crystallization were prepared through a facile in situ deposition method using rape pollen grains as a biotemplate. The functional group on the surface of the pollen grains could adsorb Fe{sup 3+}, which provided the nucleation sites for growth of iron phosphate nanoparticles. After being sintered at 600 deg. C for 10 h, the pollen grains were removed and iron phosphate hollow microspheres were obtained. A scanning electron microscope and x-ray diffraction were applied to characterize the morphology and crystalline structure of the pollen grains, iron phosphate-coated pollen grains and iron phosphate hollow microspheres. Differential scanning calorimetry and thermogravity analyses were performed to investigate the thermal behavior of the iron phosphate-coated pollen grains during the calcinations. Energy dispersive spectroscopy and Fourier transform infrared spectroscopy were utilized to investigate the interaction between the pollen grains and iron phosphate. The effect of the pollen wall on the surface morphology of these iron phosphate hollow microspheres was also proven in this work.

  10. Formation of monodisperse mesoporous silica microparticles via spray-drying.

    Science.gov (United States)

    Waldron, Kathryn; Wu, Winston Duo; Wu, Zhangxiong; Liu, Wenjie; Selomulya, Cordelia; Zhao, Dongyuan; Chen, Xiao Dong

    2014-03-15

    In this work, a protocol to synthesize monodisperse mesoporous silica microparticles via a unique microfluidic jet spray-drying route is reported for the first time. The microparticles demonstrated highly ordered hexagonal mesostructures with surface areas ranging from ~900 up to 1500 m(2)/g and pore volumes from ~0.6 to 0.8 cm(3)/g. The particle size could be easily controlled from ~50 to 100 μm from the same diameter nozzle via changing the initial solute content, or changing the drying temperature. The ratio of the surfactant (CTAB) and silica (TEOS), and the amount of water in the precursor were found to affect the degree of ordering of mesopores by promoting either the self-assembly of the surfactant-silica micelles or the condensation of the silica as two competing processes in evaporation induced self-assembly. The drying rate and the curvature of particles also affected the self-assembly of the mesostructure. The particle mesostructure is not influenced by the inlet drying temperature in the range of 92-160 °C, with even a relatively low temperature of 92 °C producing highly ordered mesoporous microparticles. The spray-drying derived mesoporous silica microparticles, while of larger sizes and more rapidly synthesized, showed a comparable performance with the conventional mesoporous silica MCM-41 in controlled release of a dye, Rhodamine B, indicating that these spray dried microparticles could be used for the immobilisation and controlled release of small molecules.

  11. Monodisperse droplet generation for microscale mass transfer studies

    Science.gov (United States)

    Roberts, Christine; Rao, Rekha; Grillet, Anne; Jove-Colon, Carlos; Brooks, Carlton; Nemer, Martin

    2011-11-01

    Understanding interfacial mass transport on a droplet scale is essential for modeling liquid-liquid extraction processes. A thin flow-focusing microfluidic channel is evaluated for generating monodisperse liquid droplets for microscale mass transport studies. Surface treatment of the microfluidic device allows creation of both oil in water and water in oil emulsions, facilitating a large parameter study of viscosity and flow rate ratios. The unusually thin channel height promotes a flow regime where no droplets form. Through confocal microscopy, this regime is shown to be highly influenced by the contact angle of the liquids with the channel. Drop sizes are found to scale with a modified capillary number. Liquid streamlines within the droplets are inferred by high speed imagery of microparticles dispersed in the droplet phase. Finally, species mass transfer to the droplet fluid is quantitatively measured using high speed imaging. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85.

  12. Electron microscopic study on aerosol-assisted synthesis of aluminum organophosphonates using flexible colloidal PS-b-PEO templates.

    Science.gov (United States)

    Kimura, Tatsuo; Yamauchi, Yusuke

    2012-09-04

    A wide variety of synthetic approaches from homogeneous precursor solutions have so far been developed for precise structural design of materials in multiscale. In organic templating approaches for porous materials design, we have recently developed a new approach to fabricate colloidal polystyrene-block-poly(oxyethylene) (PS-b-PEO) templated large pores that can be controlled in thick films of aluminum organophosphonate (AOP). In this study, we extended this approach using colloidal PS-b-PEO aggregates to aerosol-assisted synthesis for the fabrication of spherical particles. Structural variations (morphology and porous structure) depended on the synthetic conditions, which were mainly investigated by using electron microscopies (SEM and TEM). In addition to the insight on the colloidal PS-b-PEO templating of spherical pores in AOP spheres, it was found that colloidal PS-b-PEO aggregates were flexible for further design of pore shape that was strongly affected by external morphology. In this context, we proposed this method as flexible colloidal PS-b-PEO templating to fabricate unusual macroporous structures during morphological control from precursor solutions containing colloidal PS-b-PEO aggregates. The insights will be promising for precise construction of unique devices using porous materials templated by colloidal organic aggregates. In addition, we found a useful water adsorption-desorption behavior over the macroporous AOP bulky powders when the macropores were connected through large pores, which is also significant for future development of AOP-based porous materials.

  13. Concentration Effects on the Thermophoresis of Aerosol Spheres.

    Science.gov (United States)

    Keh; Ho

    1999-08-01

    The thermophoretic motion of a homogeneous suspension of identical spherical particles of arbitrary thermal conductivity and surface properties is considered under conditions of small Knudsen, Peclet, and Reynolds numbers. The effects of interaction of the individual particles are taken into explicit account by employing a unit cell model which is known to provide good predictions for the sedimentation of monodisperse suspensions of spherical particles. The appropriate equations of conservation of energy and momentum are solved for each cell, in which a spherical particle is envisaged to be surrounded by a concentric shell of suspending fluid, and the thermophoretic migration velocity of the particle is calculated for various cases. Analytical expressions of this mean particle velocity are obtained in closed form as functions of the volume fraction of the particles. Comparisons between the ensemble-averaged thermophoretic velocity of a test particle in a dilute suspension and our cell-model results are made. A parallel analysis for the sedimentation of aerosol spheres is also presented. Copyright 1999 Academic Press.

  14. Neuroscience in the public sphere.

    Science.gov (United States)

    O'Connor, Cliodhna; Rees, Geraint; Joffe, Helene

    2012-04-26

    The media are increasingly fascinated by neuroscience. Here, we consider how neuroscientific discoveries are thematically represented in the popular press and the implications this has for society. In communicating research, neuroscientists should be sensitive to the social consequences neuroscientific information may have once it enters the public sphere. Copyright © 2012 Elsevier Inc. All rights reserved.

  15. Spheres of Justice within Schools

    DEFF Research Database (Denmark)

    Sabbagh, Clara; Resh, Nura; Mor, Michal;

    2006-01-01

    This article argues that there are distinct spheres of justice within education and examines a range of justice norms and distribution rules that characterize the daily life of schools and classrooms. Moving from the macro to micro level, we identify the following five areas: the right to education...

  16. Kinetic theory of hard spheres

    NARCIS (Netherlands)

    Beijeren, H. van; Ernst, M.H.

    1979-01-01

    Kinetic equations for the hard-sphere system are derived by diagrammatic techniques. A linear equation is obtained for the one-particle-one particle equilibrium time correlation function and a nonlinear equation for the one-particle distribution function in nonequilibrium. Both equations are nonloca

  17. Voronoi diagrams on the sphere

    NARCIS (Netherlands)

    Na, H.-S.; Lee, C.-N.; Cheong, O.

    2001-01-01

    Given a set of compact sites on a sphere, we show that their spherical Voronoi diagram can be computed by computing two planar Voronoi diagrams of suitably transformed sites in the plane. We also show that a planar furthest-site Voronoi diagram can always be obtained as a portion of a

  18. Hard sphere model of atom

    CERN Document Server

    Tsekov, R

    2014-01-01

    The finite size effect of electron and nucleus is accounted for in the model of atom. Due to their hard sphere repulsion the energy of the 1s orbital decreases and the corrections amount up to 8 % in Uranium. Several models for boundary conditions on the atomic nucleus surface are discussed as well.

  19. Phase diagram of elastic spheres.

    Science.gov (United States)

    Athanasopoulou, L; Ziherl, P

    2017-02-15

    Experiments show that polymeric nanoparticles often self-assemble into several non-close-packed lattices in addition to the face-centered cubic lattice. Here, we explore theoretically the possibility that the observed phase sequences may be associated with the softness of the particles, which are modeled as elastic spheres interacting upon contact. The spheres are described by two finite-deformation theories of elasticity, the modified Saint-Venant-Kirchhoff model and the neo-Hookean model. We determine the range of indentations where the repulsion between the spheres is pairwise additive and agrees with the Hertz theory. By computing the elastic energies of nine trial crystal lattices at densities far beyond the Hertzian range, we construct the phase diagram and find the face- and body-centered cubic lattices as well as the A15 lattice and the simple hexagonal lattice, with the last two being stable at large densities where the spheres are completely faceted. These results are qualitatively consistent with observations, suggesting that deformability may indeed be viewed as a generic property that determines the phase behavior in nanocolloidal suspensions.

  20. Phase diagram of Hertzian spheres

    NARCIS (Netherlands)

    Pàmies, J.C.; Cacciuto, A.; Frenkel, D.

    2009-01-01

    We report the phase diagram of interpenetrating Hertzian spheres. The Hertz potential is purely repulsive, bounded at zero separation, and decreases monotonically as a power law with exponent 5/2, vanishing at the overlapping threshold. This simple functional describes the elastic interaction of wea

  1. Approximation on the complex sphere

    OpenAIRE

    Alsaud, Huda; Kushpel, Alexander; Levesley, Jeremy

    2012-01-01

    We develop new elements of harmonic analysis on the complex sphere on the basis of which Bernstein's, Jackson's and Kolmogorov's inequalities are established. We apply these results to get order sharp estimates of $m$-term approximations. The results obtained is a synthesis of new results on classical orthogonal polynomials, harmonic analysis on manifolds and geometric properties of Euclidean spaces.

  2. Tuning the phase diagram of colloid-polymer mixtures via Yukawa interactions

    Science.gov (United States)

    González García, Álvaro; Tuinier, Remco

    2016-12-01

    Theory that predicts the phase behavior of interacting Yukawa spheres in a solution containing nonadsorbing polymer is presented. Our approach accounts for multiple overlap of depletion zones. It is found that additional Yukawa interactions beyond hard core interactions strongly affect the location and presence of coexistence regions and phase states. The theoretical phase diagrams are compared with Monte Carlo simulations. The agreement between the two approaches supports the validity of the theoretical approximations made and confirms that, by choosing the parameters of the interaction potentials, tuning of the binodals is possible. The critical end point characterizes the phase diagram topology. It is demonstrated how an additional Yukawa interaction shifts this point with respect to the hard sphere case. Provided a certain depletant-to-colloid size ratio for which a stable colloidal gas-liquid phase coexistence takes place for hard spheres, added direct interactions turn this into a metastable gas-liquid equilibrium. The opposite case, the induction of a stable gas-liquid coexistence where only fluid-solid was present for hard spheres, is also reported.

  3. Synthesis of 3D ordered macroporous indium tin oxide using polymer colloidal crystal template

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Xue'ao; MAN; Yahui; WANG; Jianfang; LIU; Changli; WU; Wenjian

    2006-01-01

    Three-dimensional (3D) ordered macroporous indium tin oxide (ITO) is prepared using a polymer colloidal crystal template that is formed by self-assembly of the monodisperse poly(methyl methacrylate) (PMMA) microspheres. The morphologies and BET surface area of the macroporous material is examined by scanning electron microscope, transmission electron microscopy and N2 adsorption/desorption. Results indicate that the macroporous material has highly ordered arrays of the uniform pores replicated from the PMMA colloidal crystal template when the polymer colloidal crystal template is removed by calcinations at 500℃. The pore diameter (about 450 nm) of macroporous ITO slightly shrank to the PMMA microspheres. The BET surface area and pore volume of the macroporous material are 389 m2·g-1 and 0.36 cm3·g-1, respectively. Moreover, the macroporous ITO, containing 5 mol% Sn and after annealing under vacuum, shows the minimum resistivity of ρ= 8.2×10-3 Ω· cm. The conductive mechanism of macroporous ITO is discussed, and it is believed that the oxygen vacancies are the major factor for excellent electrical properties.

  4. 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.

  5. Patient-specific dosimetry for intracavitary 32P-chromic phosphate colloid therapy of cystic brain tumours.

    Science.gov (United States)

    Denis-Bacelar, Ana M; Romanchikova, Marina; Chittenden, Sarah; Saran, Frank H; Mandeville, Henry; Du, Yong; Flux, Glenn D

    2013-10-01

    (32)P-chromic phosphate colloid treatments of astrocytoma and craniopharyngioma cystic brain tumours in paediatric patients are conventionally based on a sphere model under the assumption of uniform uptake. The aims of this study were to determine the distribution of the absorbed dose delivered by (32)P on a patient-specific basis and to evaluate the accuracy with which this can be predicted from a pretherapy administration of (99m)Tc-Sn colloid. Three patients were treated with (32)P-chromic phosphate colloid following (99m)Tc-Sn colloid administrations. Convolution dosimetry was performed using pretherapy and posttherapy sequential SPECT imaging, and verified with EGSnrc Monte Carlo radiation transport simulations. Mean absorbed doses to the cyst wall and dose-volume histograms were also calculated and compared with those obtained by the sphere model approach. Highly nonuniform uptake distributions of both the (99m)Tc and (32)P colloids were observed and characterized by dose-volume histograms to the cyst wall. Mean absorbed doses delivered to the cyst wall, obtained with the convolution method, were on average 21 % (SD 18 %) and 50 % (SD 30 %) lower than those predicted by the (99m)Tc distribution and the uniform assumption of the sphere model, respectively. Absorbed doses delivered to the cyst wall by (32)P are more accurately predicted from image-based patient-specific convolution dosimetry than from simple sphere models. These results indicate the necessity to perform personalized treatment planning and verification for intracavitary irradiation of cystic brain tumours treated with radiocolloids. Patient-specific dosimetry can be used to guide the frequency and levels of repeated administrations and would facilitate data collection and comparison to support the multicentre trials necessary to progress this therapy.

  6. Soft glassy colloidal arrays in an ionic liquid: colloidal glass transition, ionic transport, and structural color in relation to microstructure.

    Science.gov (United States)

    Ueno, Kazuhide; Sano, Yuta; Inaba, Aya; Kondoh, Masashi; Watanabe, Masayoshi

    2010-10-21

    The colloidal glass transition, ionic transport, and optical properties of soft glassy colloidal arrays (SGCAs) that consist of poly(methyl methacrylate) (PMMA)-grafted silica nanoparticles (PMMA-g-NPs) and a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([C(2)mim][NTf(2)]), were investigated. At lower particle concentrations, PMMA-g-NPs were well-suspended in the IL without any aggregation or sedimentation, and the dilute suspensions showed liquid-like behavior. However, above a certain particle concentration, the suspensions became solidified and exhibited different structural colors depending on the particle concentrations. The liquid-solid transition of the SGCAs was essentially caused by colloidal glass transition. Due to the soft repulsive interaction between the particles, the effective volume fraction of the particle (ϕ(eff)) required for colloidal glass transition was higher than that of the hard sphere system and found to be approximately 0.70-0.74. The SGCA had sufficient ionic conductivity, which was greater than 10(-3) S cm(-1) at room temperature, even in the highly concentrated region. For ionic transport of the cation and the anion in the SGCAs, the decrease in diffusivity observed with the addition of the particles (D(g)/D(0)) was slightly greater for the [NTf(2)] anion than that of the [C(2)mim] cation, suggesting that the [NTf(2)] anion preferentially interacts with the PMMA chains. The SGCAs showed homogeneous, nonbrilliant, and angle-independent structural colors above the glass transition volume fraction. In addition, the color of the SGCAs changed from red to green to blue as the particle concentration increased. A linear relationship was found between the maximum wavelength of the reflection spectra and the center-to-center distance in the SGCAs.

  7. Pseudo-steady rates of crystal nucleation in suspensions of charged colloidal particles

    CERN Document Server

    Dixit, N M

    2003-01-01

    We develop an analytical model to describe crystal nucleation in suspensions of charged colloidal particles. The particles are assumed to interact with a repulsive hard-core Yukawa potential. The thermodynamic properties of the suspensions are determined by mapping onto an effective hard-sphere system using perturbation theory. Hydrodynamic effects are calculated by approximating particle interactions with the excluded shell potential. The rates of particle aggregation and dissociation from cluster surfaces in supersaturated suspensions are determined by solving the diffusion and Smoluchowski equations, respectively, which allow the calculation of pseudo-steady rates of crystal nucleation. By decoupling thermodynamic and hydrodynamic effects, we find intriguing non-monotonic dependencies of the nucleation rate on the strength and the range of particle repulsions. In particular, we find that the rate at any effective hard-sphere volume fraction can be lower than that of the hard-sphere system at that volume fr...

  8. Immobilizing LaFeO3 nanoparticles on carbon spheres for enhanced heterogeneous photo-Fenton like performance

    Science.gov (United States)

    Wang, Kaixuan; Niu, Helin; Chen, Jingshuai; Song, Jiming; Mao, Changjie; Zhang, Shengyi; Gao, Yuanhao

    2017-05-01

    LaFeO3 nanoparticles immobilized on the surface of monodisperse carbon spheres have been obtained through a facile and environmentally friendly ultrasonic assisted surface ions adsorption method. The LaFeO3/C nanocomposite was evaluated as photo-Fenton like catalyst for the degradation of Rhodamine B (RhB) under visible light irradiation (λ > 420 nm). The LaFeO3/C nanocomposite possesses high specific surface area compared with pure LaFeO3 and significantly enhanced photo-Fenton like catalytic performance. The possible formation process of the LaFeO3/C nanocomposite and the mechanism for photo-Fenton like reaction were discussed. The superior property was attributed to the synergistic effects from the photo-Fenton like process and the presence of carbon spheres. In addition, the heterogeneous process led to better recyclability of this type of catalyst.

  9. Opto-thermophoretic assembly of colloidal matter.

    Science.gov (United States)

    Lin, Linhan; Zhang, Jianli; Peng, Xiaolei; Wu, Zilong; Coughlan, Anna C H; Mao, Zhangming; Bevan, Michael A; Zheng, Yuebing

    2017-09-01

    Colloidal matter exhibits unique collective behaviors beyond what occurs at single-nanoparticle and atomic scales. Treating colloidal particles as building blocks, researchers are exploiting new strategies to rationally organize colloidal particles into complex structures for new functions and devices. Despite tremendous progress in directed assembly and self-assembly, a truly versatile assembly technique without specific functionalization of the colloidal particles remains elusive. We develop a new strategy to assemble colloidal matter under a light-controlled temperature field, which can solve challenges in the existing assembly techniques. By adding an anionic surfactant (that is, cetyltrimethylammonium chloride), which serves as a surface charge source, a macro ion, and a micellar depletant, we generate a light-controlled thermoelectric field to manipulate colloidal atoms and a depletion attraction force to assemble the colloidal atoms into two-dimensional (2D) colloidal matter. The general applicability of this opto-thermophoretic assembly (OTA) strategy allows us to build colloidal matter of diverse colloidal sizes (from subwavelength scale to micrometer scale) and materials (polymeric, dielectric, and metallic colloids) with versatile configurations and tunable bonding strengths and lengths. We further demonstrate that the incorporation of the thermoelectric field into the optical radiation force can achieve 3D reconfiguration of the colloidal matter. The OTA strategy releases the rigorous design rules required in the existing assembly techniques and enriches the structural complexity in colloidal matter, which will open a new window of opportunities for basic research on matter organization, advanced material design, and applications.

  10. Carbon spheres-assisted strategy to prepare mesoporous manganese dioxide for supercapacitor applications

    Energy Technology Data Exchange (ETDEWEB)

    Li Siheng [State Key Laboratory of Electroanalytical Chemistry, and Jilin Provincial Key Laboratory of Advanced Low-carbon Chemical Power, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin St., Changchun 130022 (China); Graduate University of Chinese Academy of Sciences, Beijing 100039 (China); Qi Li, E-mail: qil@ciac.jl.cn [State Key Laboratory of Electroanalytical Chemistry, and Jilin Provincial Key Laboratory of Advanced Low-carbon Chemical Power, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin St., Changchun 130022 (China); Lu Lehui; Wang Hongyu [State Key Laboratory of Electroanalytical Chemistry, and Jilin Provincial Key Laboratory of Advanced Low-carbon Chemical Power, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin St., Changchun 130022 (China)

    2013-01-15

    Mesoporous MnO{sub 2} microstructures with large specific surface area have been successfully synthesized by an in-situ redox precipitation method in the presence of colloidal carbon spheres. The samples of them had much higher specific surface area, pore size and pore volume than those obtained via routes without carbon spheres. The morphology, chemical compositions and porous nature of products were fully characterized. Electrochemical measurements showed that these mesoporous MnO{sub 2} could function well when used as positive electrode materials for supercapacitor. Ideal electrochemical capacitive performances and cyclic stability after 2000 galvanostatic charge-discharge cycles could be observed in 1 M neutral Na{sub 2}SO{sub 4} aqueous electrolyte with a working voltage of 1.7 V. - Graphical Abstract: Mesoporous MnO{sub 2} microstructures with large S{sub BET} were successfully synthesized by in-situ redox precipitation method in the presence of colloidal carbon spheres. Electrochemical measurements showed that these mesoporous MnO{sub 2} could be well used as electrode materials for supercapacitor. Highlights: Black-Right-Pointing-Pointer Mesoporous MnO{sub 2} was prepared by in-situ redox method assisted by carbon spheres. Black-Right-Pointing-Pointer S{sub BET}, pore size and volume were higher than MnO{sub 2} obtained without carbon spheres. Black-Right-Pointing-Pointer They could function well when used as electrode materials for supercapacitor. Black-Right-Pointing-Pointer Ideal capacitive behaviors and long cycling life showed after 2000 charge-discharge.

  11. Hard sphere-like glass transition in eye lens α-crystallin solutions.

    Science.gov (United States)

    Foffi, Giuseppe; Savin, Gabriela; Bucciarelli, Saskia; Dorsaz, Nicolas; Thurston, George M; Stradner, Anna; Schurtenberger, Peter

    2014-11-25

    We study the equilibrium liquid structure and dynamics of dilute and concentrated bovine eye lens α-crystallin solutions, using small-angle X-ray scattering, static and dynamic light scattering, viscometry, molecular dynamics simulations, and mode-coupling theory. We find that a polydisperse Percus-Yevick hard-sphere liquid-structure model accurately reproduces both static light scattering data and small-angle X-ray scattering liquid structure data from α-crystallin solutions over an extended range of protein concentrations up to 290 mg/mL or 49% vol fraction and up to ca. 330 mg/mL for static light scattering. The measured dynamic light scattering and viscosity properties are also consistent with those of hard-sphere colloids and show power laws characteristic of an approach toward a glass transition at α-crystallin volume fractions near 58%. Dynamic light scattering at a volume fraction beyond the glass transition indicates formation of an arrested state. We further perform event-driven molecular dynamics simulations of polydisperse hard-sphere systems and use mode-coupling theory to compare the measured dynamic power laws with those of hard-sphere models. The static and dynamic data, simulations, and analysis show that aqueous eye lens α-crystallin solutions exhibit a glass transition at high concentrations that is similar to those found in hard-sphere colloidal systems. The α-crystallin glass transition could have implications for the molecular basis of presbyopia and the kinetics of molecular change during cataractogenesis.

  12. Improved model for mixtures of polymers and hard spheres

    Science.gov (United States)

    D'Adamo, Giuseppe; Pelissetto, Andrea

    2016-12-01

    Extensive Monte Carlo simulations are used to investigate how model systems of mixtures of polymers and hard spheres approach the scaling limit. We represent polymers as lattice random walks of length L with an energy penalty w for each intersection (Domb-Joyce model), interacting with hard spheres of radius R c via a hard-core pair potential of range {{R}\\text{mon}}+{{R}c} , where R mon is identified as the monomer radius. We show that the mixed polymer-colloid interaction gives rise to new confluent corrections. The leading ones scale as {{L}-ν} , where ν ≈ 0.588 is the usual Flory exponent. Finally, we determine optimal values of the model parameters w and R mon that guarantee the absence of the two leading confluent corrections. This improved model shows a significantly faster convergence to the asymptotic limit L\\to ∞ and is amenable for extensive and accurate numerical simulations at finite density, with only a limited computational effort.

  13. Monte Carlo computer simulations and electron microscopy of colloidal cluster formation via emulsion droplet evaporation

    Science.gov (United States)

    Schwarz, Ingmar; Fortini, Andrea; Wagner, Claudia Simone; Wittemann, Alexander; Schmidt, Matthias

    2011-12-01

    We consider a theoretical model for a binary mixture of colloidal particles and spherical emulsion droplets. The hard sphere colloids interact via additional short-ranged attraction and long-ranged repulsion. The droplet-colloid interaction is an attractive well at the droplet surface, which induces the Pickering effect. The droplet-droplet interaction is a hard-core interaction. The droplets shrink in time, which models the evaporation of the dispersed (oil) phase, and we use Monte Carlo simulations for the dynamics. In the experiments, polystyrene particles were assembled using toluene droplets as templates. The arrangement of the particles on the surface of the droplets was analyzed with cryogenic field emission scanning electron microscopy. Before evaporation of the oil, the particle distribution on the droplet surface was found to be disordered in experiments, and the simulations reproduce this effect. After complete evaporation, ordered colloidal clusters are formed that are stable against thermal fluctuations. Both in the simulations and with field emission scanning electron microscopy, we find stable packings that range from doublets, triplets, and tetrahedra to complex polyhedra of colloids. The simulated cluster structures and size distribution agree well with the experimental results. We also simulate hierarchical assembly in a mixture of tetrahedral clusters and droplets, and find supercluster structures with morphologies that are more complex than those of clusters of single particles.

  14. Direct current electric field assembly of colloidal crystals displaying reversible structural color.

    Science.gov (United States)

    Shah, Aayush A; Ganesan, Mahesh; Jocz, Jennifer; Solomon, Michael J

    2014-08-26

    We report the application of low-voltage direct current (dc) electric fields to self-assemble close-packed colloidal crystals in nonaqueous solvents from colloidal spheres that vary in size from as large as 1.2 μm to as small as 0.1 μm. The assemblies are created rapidly (∼2 min) from an initially low volume fraction colloidal particle suspension using a simple capacitor-like electric field device that applies a steady dc electric voltage. Confocal microscopy is used to observe the ordering that is produced by the assembly method. This spatial evidence for ordering is consistent with the 6-fold diffraction patterns identified by light scattering. Red, green, and blue structural color is observed for the ordered assemblies of colloids with diameters of 0.50, 0.40, and 0.29 μm, respectively, consistent with spectroscopic measurements of reflectance. The diffraction and spectrophotometry results were found to be consistent with the theoretical Bragg's scattering expected for closed-packed crystals. By switching the dc electric field from on to off, we demonstrate reversibility of the structural color response on times scales ∼60 s. The dc electric field assembly method therefore represents a simple method to produce reversible structural color in colloidal soft matter.

  15. Yield and flow-induced phase transition in colloidal gels under startup shear

    Science.gov (United States)

    Johnson, Lilian; Landrum, Benjamin; Zia, Roseanna

    2016-11-01

    We study the micro-mechanical origins of the transition from solid-like to liquid-like behavior during flow startup of colloidal gels via large-scale dynamic simulation, with a view toward understanding connections to energy storage and phase transition. Such materials often exhibit an overshoot in stress, and prior studies of strong, dilute colloidal gels with a stringy microstructure connect this "yield" event to loss of network connectivity. Owing to the importance of Brownian transport in phase separation processes in colloids, here we study a reversible colloidal gel of hard spheres that interact via a short-range attraction of several kT, for which Brownian motion can lead to rapid quiescent coarsening. In the present study, we interrogate the shear stress for a range of imposed flow strengths, monitoring particle-level structure and dynamics, to determine the microscopic picture of gel yield. Our detailed studies of the microstructural evolution and macroscopic response during startup provide insight into the phase behavior during yield. We present a new model of stress development, phase transition, and structural evolution during transient yield in colloidal gels for which ongoing phase separation informs gel phenomenology.

  16. Self-assembly of microcapsules via colloidal bond hybridization and anisotropy.

    Science.gov (United States)

    Evers, Chris H J; Luiken, Jurriaan A; Bolhuis, Peter G; Kegel, Willem K

    2016-06-16

    Particles with directional interactions are promising building blocks for new functional materials and may serve as models for biological structures. Mutually attractive nanoparticles that are deformable owing to flexible surface groups, for example, may spontaneously order themselves into strings, sheets and large vesicles. Furthermore, anisotropic colloids with attractive patches can self-assemble into open lattices and the colloidal equivalents of molecules and micelles. However, model systems that combine mutual attraction, anisotropy and deformability have not yet been realized. Here we synthesize colloidal particles that combine these three characteristics and obtain self-assembled microcapsules. We propose that mutual attraction and deformability induce directional interactions via colloidal bond hybridization. Our particles contain both mutually attractive and repulsive surface groups that are flexible. Analogously to the simplest chemical bond--in which two isotropic orbitals hybridize into the molecular orbital of H2--these flexible groups redistribute on binding. Via colloidal bond hybridization, isotropic spheres self-assemble into planar monolayers, whereas anisotropic snowman-shaped particles self-assemble into hollow monolayer microcapsules. A modest change in the building blocks thus results in much greater complexity of the self-assembled structures. In other words, these relatively simple building blocks self-assemble into markedly more complex structures than do similar particles that are isotropic or non-deformable.

  17. Thermodynamic perturbation theory for self-assembling mixtures of divalent single patch colloids.

    Science.gov (United States)

    Marshall, Bennett D; Chapman, Walter G

    2014-07-28

    In this work we extend Wertheim's thermodynamic perturbation theory (TPT) to binary mixtures (species A and species B) of patchy colloids were each species has a single patch which can bond a maximum of twice (divalent). Colloids are treated as hard spheres with a directional conical association site. We restrict the system such that only patches between unlike species share attractions; meaning there are AB attractions but no AA or BB attractions. The theory is derived in Wertheim's two density formalism for one site associating fluids. Since the patches are doubly bondable, associated chains, of all chain lengths, as well as 4-mer rings consisting of two species A and two species B colloids are accounted for. With the restriction of only AB attractions, triatomic rings of doubly bonded colloids, which dominate in the corresponding pure component case, cannot form. The theory is shown to be in good agreement with Monte Carlo simulation data for the structure and thermodynamics of these patchy colloid mixtures as a function of temperature, density, patch size and composition. It is shown that 4-mer rings dominate at low temperature, inhibiting the polymerization of the mixture into long chains. Mixtures of this type have been recently synthesized by researchers. This work provides the first theory capable of accurately modeling these mixtures.

  18. Self-assembly of microcapsules via colloidal bond hybridization and anisotropy

    Science.gov (United States)

    Evers, Chris H. J.; Luiken, Jurriaan A.; Bolhuis, Peter G.; Kegel, Willem K.

    2016-06-01

    Particles with directional interactions are promising building blocks for new functional materials and may serve as models for biological structures. Mutually attractive nanoparticles that are deformable owing to flexible surface groups, for example, may spontaneously order themselves into strings, sheets and large vesicles. Furthermore, anisotropic colloids with attractive patches can self-assemble into open lattices and the colloidal equivalents of molecules and micelles. However, model systems that combine mutual attraction, anisotropy and deformability have not yet been realized. Here we synthesize colloidal particles that combine these three characteristics and obtain self-assembled microcapsules. We propose that mutual attraction and deformability induce directional interactions via colloidal bond hybridization. Our particles contain both mutually attractive and repulsive surface groups that are flexible. Analogously to the simplest chemical bond—in which two isotropic orbitals hybridize into the molecular orbital of H2—these flexible groups redistribute on binding. Via colloidal bond hybridization, isotropic spheres self-assemble into planar monolayers, whereas anisotropic snowman-shaped particles self-assemble into hollow monolayer microcapsules. A modest change in the building blocks thus results in much greater complexity of the self-assembled structures. In other words, these relatively simple building blocks self-assemble into markedly more complex structures than do similar particles that are isotropic or non-deformable.

  19. DEPLETION POTENTIAL OF COLLOIDS:A DIRECT SIMULATION STUDY

    Institute of Scientific and Technical Information of China (English)

    LI; Wei-hua(

    2001-01-01

    [1]Asakura S, Oosawa F. Surface tension of high-poly-mer solution [J]. J Chem Phys, 1954, 22: 1255~ 1255.[2]Ye X, Narayanan T, Tong P, et al. Depletion interactions in colloid-polymer mixtures [J]. Phys Rev E, 1996, 54: 6500~6510.[3]Kaplan P D, Faucheux L P, Libchaber A J. Direct observation of the entropic potential in a binary suspension [J]. Phys Rev Lett, 1994, 73: 2793~2796.[4]Ohshima Y N, Sakagami H, Okumoto K, et al. Direct measurement of infinite simal depletion force in a colloid-polymer mixture by laser radiation pressure [J]. Phys Rev Lett, 1997, 78: 3963~3966.[5]Dinsmore A D, Yodh A G, Pine D J. Entropic control particle motion using passive surface microstructures [J]. Nature (London), 1996, 383: 239~242.[6]Dinsmore A D, Wong D T, Nelson P, et al. Hard spheres in vecicles: curvature-induced forces and particle-induced curvature [J]. Phys Rev Lett, 1998, 80: 409~412.[7]Gtzelmann B, Evans R, Dietrich S. Depletion forces in fluids [J]. Phys Rev E, 1998, 57: 6785~6800.[8]Miao Y, Cates M E, Lekkerkerker H N W. Depletion force in colloidal systems [J]. Physica A, 1995, 222: 10~24.[9]Biben J, Bladon P, Frenkel D. Depletion effects in binary hard-sphere fluids [J]. J Phys: Condens Matter, 1996, 8: 10799~10821.[10]Dickman R, Attard P, Simonian V. Entropic forces in binary hard sphere mixture: Theory and simulation [J]. J Chem Phys, 1997, 107: 205~213.[11]Bennett C H. Efficient estimation of free energy differences from Monte Carlo data [J]. J Comput Phys, 1976, 22: 245~268; see also Allen M P, Tildesley D J. Computer Simulation of Liquids (Chap.7) [M]. Oxford: Clarendon Press. 1994.

  20. Controlled synthesis and magnetic properties of monodispersed ceria nanoparticles

    Directory of Open Access Journals (Sweden)

    Sumeet Kumar

    2015-02-01

    Full Text Available In the present study, monodispersed CeO2 nanoparticles (NPs of size 8.5 ± 1.0, 11.4 ± 1.0 and 15.4 ± 1.0 nm were synthesized using the sol-gel method. Size-dependent structural, optical and magnetic properties of as-prepared samples were investigated by X-ray diffraction (XRD, field emission scanning electron microscope (FE-SEM, high resolution transmission electron microscopy (HR-TEM, ultra-violet visible (UV-VIS spectroscopy, Raman spectroscopy and vibrating sample magnetometer (VSM measurements. The value of optical band gap is calculated for each particle size. The decrease in the value of optical band gap with increase of particle size may be attributed to the quantum confinement, which causes to produce localized states created by the oxygen vacancies due to the conversion of Ce4+ into Ce3+ at higher calcination temperature. The Raman spectra showed a peak at ∼461 cm-1 for the particle size 8.5 nm, which is attributed to the 1LO phonon mode. The shift in the Raman peak could be due to lattice strain developed due to variation in particle size. Weak ferromagnetism at room temperature is observed for each particle size. The values of saturation magnetization (Ms, coercivity (Hc and retentivity (Mr are increased with increase of particle size. The increase of Ms and Mr for larger particle size may be explained by increase of density of oxygen vacancies at higher calcination temperature. The latter causes high concentrations of Ce3+ ions activate more coupling between the individual magnetic moments of the Ce ions, leading to an increase of Ms value with the particle size. Moreover, the oxygen vacancies may also produce magnetic moment by polarizing spins of f electrons of cerium (Ce ions located around oxygen vacancies, which causes ferromagnetism in pure CeO2 samples.