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Sample records for binary colloidal crystals

  1. 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.

  2. Selective cleavage of periodic mesoscale structures: two-dimensional replication of binary colloidal crystals into dimpled gold nanoplates.

    Science.gov (United States)

    Kuroda, Yoshiyuki; Sakamoto, Yasuhiro; Kuroda, Kazuyuki

    2012-05-23

    Specific crystallographic planes of binary colloidal crystals consisting of silica nanoparticles are two-dimensionally replicated on the surface of gold nanoplates. The selectivity of the surface patterns is explained by the geometrical characteristics of the binary colloidal crystals as templates. The binary colloidal crystals with the AlB(2)- and NaZn(13)-type structures are fabricated from aqueous dispersions of stoichiometrically mixed silica nanoparticles with different sizes. The stoichiometry is precisely controlled on the basis of a seed growth of silica nanoparticles. Dimpled gold nanoplates are formed by the two-dimensional growth of gold between partially cleaved surfaces of templates. The selectivity of the surface patterns is explained using the AlB(2)-type binary colloidal crystal as a template. The surface pattern is determined by the preferential cleavage of the plane with the lowest density of particle-particle connections. The tendency to form well-defined cleavage in binary colloidal crystals is crucial to formation of dimpled gold nanoplates, which is explained using the NaZn(13)-type binary colloidal crystal as a template. Its complex structure does not show well-defined cleavage, and only distorted nanoplates are obtained. Therefore, the mechanism of the two-dimensional replication of binary colloidal crystals is reasonably explained on the basis of their periodic mesoscale structures and crystal-like properties.

  3. Preparation of highly permeable BPPO microfiltration membrane with binary porous structures on a colloidal crystal substrate by the breath figure method.

    Science.gov (United States)

    Yuan, Hua; Yu, Bing; Cong, Hailin; Peng, Qiaohong; Yang, Zhen; Luo, Yongli; Chi, Ming

    2016-01-01

    A highly permeable brominated poly(phenylene oxide) (BPPO) microfiltration membrane with binary porous structures was fabricated by combination of the breath figure and colloidal crystal template methods. The pore size in the bottom layer of the membrane was adjusted by the diameter of SiO2 microspheres in the colloidal crystal template, while the pore size in the top layer of the membrane was adjusted by varying the BPPO concentration in the casting solution. The permeability of the membrane cast on the colloidal crystal substrate was much higher than that of the membrane cast on a bare silicon wafer. The binary porous BPPO membrane with high permeability and antifouling property was used for microfiltration applications.

  4. Manipulation of colloidal crystallization

    NARCIS (Netherlands)

    Vermolen, E.C.M.

    2008-01-01

    Colloidal particles (approximately a micrometer in diameter) that are dispersed in a fluid, behave thermodynamically similar to atoms and molecules: at low concentrations they form a fluid, while at high concentrations they can crystallize into a colloidal crystal to gain entropy. The analogy with m

  5. 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.

  6. 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

  7. 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.

  8. Binary Colloidal Alloy Test-5: Phase Separation

    Science.gov (United States)

    Lynch, Matthew; Weitz, David A.; Lu, Peter J.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Phase Separation (BCAT-5-PhaseSep) experiment will photograph initially randomized colloidal samples onboard the ISS to determine their resulting structure over time. This allows the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-PhaseSep studies collapse (phase separation rates that impact product shelf-life); in microgravity the physics of collapse is not masked by being reduced to a simple top and bottom phase as it is on Earth.

  9. Crystallization of DNA-coated colloids.

    Science.gov (United States)

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S; Weck, Marcus; Pine, David J

    2015-06-16

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids.

  10. Fabricating colloidal crystals and construction of ordered nanostructures

    Directory of Open Access Journals (Sweden)

    Sun Zhiqiang

    2006-01-01

    Full Text Available AbstractColloidal crystals of polymeric or inorganic microspheres are of extensive interest due to their potential applications in such as sensing, optics, photonic bandgap and surface patterning. The article highlights a set of approaches developed in our group, which are efficient to prepare colloidal crystals with ordered voids, patterned colloidal crystals on non-planar surfaces, heterogeneous colloidal crystals of different building blocks, colloidal crystals composed of non-spherical polyhedrons, and colloidal crystals of non-close-packed colloidal microspheres in particular. The use of these colloidal crystals as templates for different microstructures range from nanoscale to micron-scale is also summarized.

  11. 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.

  12. Collective sliding states for colloidal molecular crystals

    Energy Technology Data Exchange (ETDEWEB)

    Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia [Los Alamos National Laboratory

    2008-01-01

    We study the driving of colloidal molecular crystals over periodic substrates such as those created with optical traps. The n-merization that occurs in the colloidal molecular crystal states produces a remarkably rich variety of distinct dynamical behaviors, including polarization effects within the pinned phase and the formation of both ordered and disordered sliding phases. Using computer simulations, we map the dynamic phase diagrams as a function of substrate strength for dimers and trimers on a triangular substrate, and correlate features on the phase diagram with transport signatures.

  13. Laser diffraction analysis of colloidal crystals

    Energy Technology Data Exchange (ETDEWEB)

    Sogami, Ikuo S.; Shinohara, Tadatomi; Yoshiyama, Tsuyoshi [Kyoto Sangyo Univ., Department of Physics, Kyoto (Japan)

    2001-10-01

    Laser diffraction analysis is made on crystallization in salt-free aqueous suspensions of highly-charged colloidal particles for semi-dilute specimens of concentration 0.1-10.0 vol%. Kossel diffraction patterns which represent faithfully accurate information on lattice symmetries in the suspensions enable us to investigate the time evolution of colloidal crystals. The results show that the crystallization proceeds by way of the following intermediate phase transitions: two-dimensional hcp structure {yields} random layer structure {yields} layer structure with one sliding degree of freedom {yields} stacking disorder structure {yields} stacking structure with multivariant periodicity {yields} fcc twin structure with twin plane (111) {yields} normal fcc structure {yields} bcc twin structure with twin plane (11-bar2) or (1-bar12) {yields} normal bcc structure. For concentrated suspensions (>2 vol %), the phase transition ceases to proceed at the normal fcc structure. (author)

  14. 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.

  15. Colloidal crystals by electrospraying polystyrene nanofluids

    Science.gov (United States)

    2013-01-01

    This work introduces the electrospray technique as a suitable option to fabricate large-scale colloidal nanostructures, including colloidal crystals, in just a few minutes. It is shown that by changing the deposition conditions, different metamaterials can be fabricated: from scattered monolayers of polystyrene nanospheres to self-assembled three-dimensional ordered nanolayers having colloidal crystal properties. The electrospray technique overcomes the main problems encountered by top-down fabrication approaches, largely simplifying the experimental setup. Polystyrene nanospheres, with 360-nm diameter, were typically electrosprayed using off-the-shelf nanofluids. Several parameters of the setup and deposition conditions were explored, namely the distance between electrodes, nanofluid conductivity, applied voltage, and deposition rate. Layers thicker than 20 μm and area of 1 cm2 were typically produced, showing several domains of tens of microns wide with dislocations in between, but no cracks. The applied voltage was in the range of 10 kV, and the conductivity of the colloidal solution was in the range of 3 to 4 mS. Besides the morphology of the layers, the quality was also assessed by means of optical reflectance measurements showing an 80% reflectivity peak in the vicinity of 950-nm wavelength. PMID:23311494

  16. Colloidal cholesteric liquid crystal in spherical confinement

    Science.gov (United States)

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-08-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter.

  17. Photochemical manipulation of colloidal structures in liquid-crystal colloids

    Science.gov (United States)

    Yamamoto, T.; Tabe, Y.; Yokoyama, H.

    2007-05-01

    We investigated photochemical manipulation of physical properties and colloidal structures in liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

  18. Two-substrate vertical deposition for stable colloidal crystal chips

    Institute of Scientific and Technical Information of China (English)

    CHEN Xin; SUN Zhiqiang; CHEN Zhimin; ZHANG Kai; YANG Bai

    2005-01-01

    By combining vertical deposition with micromolding in capillaries method, we have demonstrated the two-substrate vertical deposition, an alternative and versatile procedure for fabricating high-quality stable colloidal crystal chips. Apparent bright colors, special UV-vis spectra, scanning electron microscopy (SEM) and atomic force microscopy (AFM) images all prove that high-quality colloidal crystal structures are formed in between the two substrates. During the two-substrate vertical deposition for colloidal crystal chips, capillary force and evaporation of the medium are critical to the formation of the colloidal crystals; while the confinement in between two close substrates makes the resulting colloidal crystal chips more stable. Due to the excellent stability, these colloidal crystal chips can be used to construct some composite optical devices via a simpler and more flexible process. Meanwhile, they can also be further used as the templates for ordered multiporous materials.

  19. Recent research progress in wettability of colloidal crystals

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The wettability of solid surfaces has attracted extensive interest in both theoretical research and industrial applications. This paper reviews recent research progress in the fabrication and applications of the colloidal crystals with special wettability. Based on the modified equation of Wenzel and Cassie, the colloidal crystals with special wettability have been obtained by either application of the intrinsic rough structure or modification of the surface chemical composition. Some typical applications of colloidal crystals with special wettability have also been demonstrated.

  20. Fabrication and Characterization of Colloidal Crystal Thin Films

    Science.gov (United States)

    Rodriguez, I.; Ramiro-Manzano, F.; Meseguer, F.; Bonet, E.

    2011-01-01

    We present a laboratory experiment that allows undergraduate or graduate students to get introduced to colloidal crystal research concepts in an interesting way. Moreover, such experiments and studies can also be useful in the field of crystallography or solid-state physics. The work concerns the growth of colloidal crystal thin films obtained…

  1. 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...

  2. Colloidal-crystal-assisted patterning of crystalline materials.

    Science.gov (United States)

    Li, Cheng; Qi, Limin

    2010-04-06

    Colloidal crystals have shown great potential as versatile templates for the fabrication of patterned micro- and nanostructures with complex architectures and novel properties. The patterning of functional crystalline materials in two and three dimensions is essential to the realization of their applications in many technologically important fields. This article highlights some recent progress in the fabrication of 2D and 3D patterned crystalline materials with the assistance of colloidal crystals. By combining a bioinspired synthetic strategy based on a transient amorphous phase with a colloidal-crystal templating method, unique 3D ordered macroporous (3DOM) calcite single crystals can be created. Moreover, patterned arrays of regular ZnO nanopillars with controlled size, shape, and orientation can be fabricated via a facile wet chemical approach by using masks derived from monolayer colloidal crystals (MCC).

  3. Combining the Masking and Scaffolding Modalities of Colloidal Crystal Templates: Plasmonic Nanoparticle Arrays with Multiple Periodicities

    OpenAIRE

    Yang, Shikuan; Slotcavage, Daniel; Mai, John D.; Liang, Wansheng; Xie, Yuliang; Chen, Yuchao; Huang, Tony Jun

    2014-01-01

    Surface patterns with prescribed structures and properties are highly desirable for a variety of applications. Increasing the heterogeneity of surface patterns is frequently required. This work opens a new avenue toward creating nanoparticle arrays with multiple periodicities by combining two generally separately applied modalities (i.e., scaffolding and masking) of a monolayer colloidal crystal (MCC) template. Highly ordered, loosely packed binary and ternary surface patterns are realized by...

  4. Vortexlike topological defects in nematic colloids: chiral colloidal dimers and 2D crystals.

    Science.gov (United States)

    Tkalec, U; Ravnik, M; Zumer, S; Musevic, I

    2009-09-18

    We show that chiral ordering of the underlying complex fluid strongly influences defect formation and colloidal interactions. Nonsingular defect loops with a topological charge -2 are observed, with a cross section identical to hyperbolic vortices in magnetic systems. These loops are binding spontaneously formed pairs of colloidal particles and dimers, which are chiral objects. Chiral dimer-dimer interaction weakly depends on the chirality of dimers and leads to the assembly of 2D nematic colloidal crystals of pure or "mixed" chirality, intercalated with a lattice of nonsingular vortexlike defects.

  5. 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.

  6. Synthetic Strategies Toward DNA-Coated Colloids that Crystallize.

    Science.gov (United States)

    Wang, Yufeng; Wang, Yu; Zheng, Xiaolong; Ducrot, Étienne; Lee, Myung-Goo; Yi, Gi-Ra; Weck, Marcus; Pine, David J

    2015-08-26

    We report on synthetic strategies to fabricate DNA-coated micrometer-sized colloids that, upon thermal annealing, self-assemble into various crystal structures. Colloids of a wide range of chemical compositions, including poly(styrene), poly(methyl methacrylate), titania, silica, and a silica-methacrylate hybrid material, are fabricated with smooth particle surfaces and a dense layer of surface functional anchors. Single-stranded oligonucleotides with a short sticky end are covalently grafted onto particle surfaces employing a strain-promoted alkyne-azide cycloaddition reaction resulting in DNA coatings with areal densities an order of magnitude higher than previously reported. Our approach allows the DNA-coated colloids not only to aggregate upon cooling but also to anneal and rearrange while still bound together, leading to the formation of colloidal crystal compounds when particles of different sizes or different materials are combined.

  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. Gelled colloidal crystals as tunable optical filters for spectrophotometers

    Science.gov (United States)

    Sugao, Yukihiro; Onda, Sachiko; Toyotama, Akiko; Takiguchi, Yoshihiro; Sawada, Tsutomu; Hara, Shigeo; Nishikawa, Suguru; Yamanaka, Junpei

    2016-08-01

    We examined the performance of charged colloidal crystals immobilized in a polymer gel as tunable optical filters. The colloidal crystals of charged silica particles (particle diameter = 121 nm; particle concentration = 3.5 vol %; and Bragg wavelength λB = 630-720 nm) were produced by unidirectional crystallization under a temperature gradient. Photocurable gelation reagents were dissolved in the sample beforehand; this enabled gel immobilization of the crystals under ultraviolet illumination. The crystals had dimensions of more than 25 mm2 in area and 1 mm in thickness, and spatial λB variations of less than 1%. Upon mechanical compression, λB values shifted linearly and reversibly over almost the entire visible spectrum. Using the gelled crystals as tunable optical filters, we measured the transmittance spectra of various samples and found them to be in close agreement with those determined using a spectrophotometer equipped with optical gratings.

  9. Colloidal spirals in nematic liquid crystals.

    Science.gov (United States)

    Senyuk, Bohdan; Pandey, Manoj B; Liu, Qingkun; Tasinkevych, Mykola; Smalyukh, Ivan I

    2015-12-07

    One of the central experimental efforts in nematic colloids research aims to explore how the interplay between the geometry of particles along with the accompanying nematic director deformations and defects around them can provide a means of guiding particle self-assembly and controlling the structure of particle-induced defects. In this work, we design, fabricate, and disperse low-symmetry colloidal particles with shapes of spirals, double spirals, and triple spirals in a nematic fluid. These spiral-shaped particles, which are controlled by varying their surface functionalization to provide tangential or perpendicular boundary conditions of the nematic molecular alignment, are found inducing director distortions and defect configurations with non-chiral or chiral symmetry. Colloidal particles also exhibit both stable and metastable multiple orientational states in the nematic host, with a large number of director configurations featuring both singular and solitonic nonsingular topological defects accompanying them, which can result in unusual forms of colloidal self-assembly. Our findings directly demonstrate how the symmetry of particle-generated director configurations can be further lowered, or not, as compared to the low point group symmetry of solid micro-inclusions, depending on the nature of induced defects while satisfying topological constraints. We show that achiral colloidal particles can cause chiral symmetry breaking of elastic distortions, which is driven by complex three-dimensional winding of induced topological line defects and solitons.

  10. Kossel diffraction and conformation investigation of colloidal crystals

    Science.gov (United States)

    Yang, Hao; Wang, Chao; Sun, Zhibin; Cao, Song; Zhai, Guangjie; Li, Ming

    2010-10-01

    Kossel-line diffraction method is an important way to measure the structure of crystals. Colloidal crystal is one of the hotspots on the condensed physics research. The paper investigates the kinetics process of crystallization on several hundreds nanometer particles in aqueous. In order to obtain the diffraction image, a 473nm wavelength laser is used to irradiate samples, and then the Kossel-line image of sample is projected onto the translucent screen and recorded by IEEE 1394 charge coupled device (CCD) cameras. Especially, gravity convection effects can be eliminated under microgravity environment, therefore the research of growth mechanism of colloidal crystals in the space has great scientific significance. The crystallization processes of three kinds of colloidal solution are investigated in the temperature field and electric field by means of the shear-flow assisted. Finally, laser diffraction images and white conformation images can be analyzed for exploring the phase-change rule of colloidal crystals. Besides, parameters can be adjusted online by remote control function in order to improve the flexibility of experiments.

  11. 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 .

  12. Self-assembly of latex particles for colloidal crystals

    Institute of Scientific and Technical Information of China (English)

    Zhirong Li; Jingxia wang; Yanlin Song

    2011-01-01

    Self-assembly of latex particles is of great importance for fabricating various functional colloidal crystals.In this paper,we review recent research on the self-assembly of latex particles for colloidal crystals,covering the assembly forces and various assembly approaches of latex particles,including self-assembly by gravity sedimentation,vertical deposition,physical confinement,electric field,and magnetic field.Furthermore,some simple methods for assembling latex particles such as spin coating,spray coating,and printing are also summarized.

  13. Control over colloidal crystallization by shear and electric fields

    NARCIS (Netherlands)

    Wu, Y.L.

    2007-01-01

    We used shear flow and an electric field to control colloidal crystallization. The structures were examined in situ with confocal microscopy. For experiments under shear, a new parallel plate shear cell was designed. It had a zero-velocity plane that was stationary with respect to the microscope. Th

  14. Overview: Experimental studies of crystal nucleation: Metals and colloids

    Science.gov (United States)

    Herlach, Dieter M.; Palberg, Thomas; Klassen, Ina; Klein, Stefan; Kobold, Raphael

    2016-12-01

    Crystallization is one of the most important phase transformations of first order. In the case of metals and alloys, the liquid phase is the parent phase of materials production. The conditions of the crystallization process control the as-solidified material in its chemical and physical properties. Nucleation initiates the crystallization of a liquid. It selects the crystallographic phase, stable or meta-stable. Its detailed knowledge is therefore mandatory for the design of materials. We present techniques of containerless processing for nucleation studies of metals and alloys. Experimental results demonstrate the power of these methods not only for crystal nucleation of stable solids but in particular also for investigations of crystal nucleation of metastable solids at extreme undercooling. This concerns the physical nature of heterogeneous versus homogeneous nucleation and nucleation of phases nucleated under non-equilibrium conditions. The results are analyzed within classical nucleation theory that defines the activation energy of homogeneous nucleation in terms of the interfacial energy and the difference of Gibbs free energies of solid and liquid. The interfacial energy acts as barrier for the nucleation process. Its experimental determination is difficult in the case of metals. In the second part of this work we therefore explore the potential of colloidal suspensions as model systems for the crystallization process. The nucleation process of colloids is observed in situ by optical observation and ultra-small angle X-ray diffraction using high intensity synchrotron radiation. It allows an unambiguous discrimination of homogeneous and heterogeneous nucleation as well as the determination of the interfacial free energy of the solid-liquid interface. Our results are used to construct Turnbull plots of colloids, which are discussed in relation to Turnbull plots of metals and support the hypothesis that colloids are useful model systems to investigate crystal

  15. Sedimentation-diffusion equilibrium of binary mixtures of charged colloids including volume effects

    NARCIS (Netherlands)

    Biesheuvel, P.M.; Lyklema, J.

    2005-01-01

    We describe the sedimentation-diffusion equilibrium of binary mixtures of charged colloids in the presence of small ions and for non-dilute conditions, by extending the work of Biben and Hansen (1994 J. Phys.: Condens. Matter 6 A345). For a monocomponent system, they included a Carnahan-Starling har

  16. Shear-driven aggregation of binary colloids for randomly distributing nanoparticles in a matrix.

    Science.gov (United States)

    Meng, Xia; Wu, Hua; Morbidelli, Massimo

    2016-04-20

    We propose a methodology for preparing composite materials where A nanoparticles (NPs) are uniformly and randomly distributed inside a matrix of B NPs. It is based on intense shear-driven aggregation of binary colloids composed of A and B NPs, without using any additives. Its feasibility has been demonstrated using stable binary colloids composed of poly-methyl methacrylate (PMMA) particles and polystyrene (PS) particles. The PS particles alone undergo shear-driven aggregation (shear-active), while the PMMA particles alone do not exhibit any aggregation under the same conditions (shear-inactive). It is found that the shear-driven aggregation of the binary colloids does occur, and the formed clusters are composed of both the "shear-active" PS and "shear-inactive" PMMA particles. The SEM pictures demonstrate that the PMMA particles are uniformly and randomly distributed among the PS particles in the clusters, thus confirming the feasibility of the proposed methodology. The mechanism leading to the aggregation of the binary colloids has been discussed based on the experimental observations.

  17. 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.

  18. STRUCTURE FORMATION OF COLLOIDS IN NEMATIC LIQUID CRYSTALS

    Directory of Open Access Journals (Sweden)

    B.I.Lev

    2003-01-01

    Full Text Available We investigated the behaviour of colloidal particles suspended in nematic liquid crystals. These colloidal particles interact through elastic deformation of the nematic director field which can result in nontrivial collective behavior, leading to the formation of spatially modulated structures. In this paper, the formation of lattice structures is described both by computer simulations and by analytical theory. Effective interactions of the pairs of spherical macroparticles suspended in nematic liquid crystals have been suggested by many authors. Using these pairwise interactions, spatial structures are obtained by means of dynamic simulations. We have suggested a number of possible structures, which may be formed in multi-macroparticle systems. Regions of temperatures and concentrations are determined in which such a structure might appear.

  19. Influence of colloidal particle transfer on the quality of self-assembling colloidal photonic crystal under confined condition

    Institute of Scientific and Technical Information of China (English)

    赵永强; 李娟; 刘秋艳; 董文钧; 陈本永; 李超荣

    2015-01-01

    The relationship between colloidal particle transfer and quality of colloidal photonic crystal (CPC) is investigated by comparing colloidal particle self-assembling under the vertical channel (VC) and horizontal channel (HC) conditions. Both the theoretical analyses and the experimental measurements indicate that crystal quality depends on the stability of mass transfer. For the VC, colloidal particle transfer takes place in a stable laminar flow, which is conducive to forming high-quality crystal. In contrast, it happens in an unstable turbulent flow for the HC. Crystals with cracks and uneven surface formed under the HC condition can be seen from the images of field emission scanning electron microscope (SEM) and three-dimensional (3D) laser scanning microscope (LSM), respectively.

  20. Preparation of Three-Dimensional Photonic Crystals of Zirconia by Electrodeposition in a Colloidal Crystals Template

    Directory of Open Access Journals (Sweden)

    Lei Pan

    2016-07-01

    Full Text Available Three-dimensional photonic crystals of zirconia were prepared by electrodeposition in a colloidal crystals template following calcination at 500 °C. Scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, and reflectance spectroscopy were employed to characterize the photonic crystals of zirconia. It was found that hydrated zirconium ions could penetrate the colloidal crystals template and reach the substrate easily by electrodeposition, which resulted in stronger bonding between the substrate and the as-deposited membrane. Moreover, the electrodeposited membrane had low water content, leading to a low amount of shrinkage during calcination. Both these properties could suppress detachment from the substrate upon removal of the colloidal crystals template. Therefore, the three-dimensional photonic crystals of zirconia synthesized in this study exhibited very good preservation of the ordered structures of the colloidal crystals template with a high density. A peak of reflection higher than 70% was formed in the reflectance spectrum because of the strong diffraction of the ordered structures.

  1. Crystallization and Growth of Colloidal Nanocrystals

    CERN Document Server

    Leite, Edson Roberto

    2012-01-01

    Since the size, shape, and microstructure of nanocrystalline materials strongly impact physical and chemical properties, the development of new synthetic routes to  nanocrystals with controlled composition and morphology is a key objective of the nanomaterials community. This objective is dependent on control of the nucleation and growth mechanisms that occur during the synthetic process, which in turn requires a fundamental understanding of both classical nucleation and growth and non-classical growth processes in nanostructured materials.  Recently, a novel growth process called Oriented Attachment (OA) was identified which appears to be a fundamental mechanism during the development of nanoscale  materials. OA is a special case of aggregation that provides an important route by which nanocrystals grow, defects are formed, and unique—often symmetry-defying—crystal morphologies can be produced. This growth mechanism involves reversible self-assembly of primary nanocrystals followed by reorientati...

  2. Densification and crystallization behaviour of colloidal cordierite-type gels

    Directory of Open Access Journals (Sweden)

    LJILJANA KOSTIC-GVOZDENOVIC

    2001-05-01

    Full Text Available Three cordierite-type gels were prepared from an aqueous solution of Mg(NO32, a boehmite sol and silica sols of very small particle sizes. The effect of varying the silica particle size on the crystallization and densification behaviour was studied. Phase development was examined by thermal analysis and X-ray diffraction, while the densification behaviour was characterized by measuring the linear shrinkage of pellets. The activation energy of densification by viscous flow was determined using the Franckel model for non-isothermal conditions and a constant heating rate. The results show that spinel crystallizes from the colloidal gels prior to cristobalite, and their reaction gives a-cordierite, which is specific for three-phase gels. Decreasing the silica particles size lowers the cristobalite crystallization temperature and the a-cordierite formation temperature. The activation energy of densification by viscous flow is lower and the densification more efficient, the smaller the silica particles are.

  3. Colloidal interactions and transport in nematic liquid crystals.

    Science.gov (United States)

    Tatarkova, S A; Burnham, D R; Kirby, A K; Love, G D; Terentjev, E M

    2007-04-13

    We describe a new nematic liquid-crystal colloid system which is characterized by both charge stabilization of the particles and an interaction force. We estimate the effective charge of the particles by electrophoretic measurements and find that in such systems the director anchoring energy W is very low and the particles have little director distortion around them. The interaction force is created by producing a radial distribution of the nematic order parameter around a locally isotropic region created by ir laser heating. We theoretically describe this as being due to the induced flexoelectric polarization, the quadrupolar symmetry of which provides the required long-range force acting on charged particles.

  4. An effective packing density of binary cubic crystals

    Science.gov (United States)

    Eremin, I. E.; Eremina, V. V.; Sychev, M. S.; Moiseenko, V. G.

    2015-04-01

    The methodology of effective macroscopic calculation of numerical values of internuclear distances in binary crystals of a cubic crystal system is based on the use of coefficients of the structural packing density of the crystal lattice. The possibility of combining the reference data on the main physicochemical parameters of the substance is implemented by synthesis of the corresponding mathematical models.

  5. 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.

  6. 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.

  7. 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.

  8. Straining soft colloids in aqueous nematic liquid crystals

    Science.gov (United States)

    Mushenheim, Peter C.; Pendery, Joel S.; Weibel, Douglas B.; Spagnolie, Saverio E.; Abbott, Nicholas L.

    2016-05-01

    Liquid crystals (LCs), because of their long-range molecular ordering, are anisotropic, elastic fluids. Herein, we report that elastic stresses imparted by nematic LCs can dynamically shape soft colloids and tune their physical properties. Specifically, we use giant unilamellar vesicles (GUVs) as soft colloids and explore the interplay of mechanical strain when the GUVs are confined within aqueous chromonic LC phases. Accompanying thermal quenching from isotropic to LC phases, we observe the elasticity of the LC phases to transform initially spherical GUVs (diameters of 2-50 µm) into two distinct populations of GUVs with spindle-like shapes and aspect ratios as large as 10. Large GUVs are strained to a small extent (R/r minor radii, respectively), consistent with an LC elasticity-induced expansion of lipid membrane surface area of up to 3% and conservation of the internal GUV volume. Small GUVs, in contrast, form highly elongated spindles (1.54 materials and suggest previously unidentified designs of LC-based responsive and reconfigurable materials.

  9. Photonic Crystal Fibre SERS Sensors Based on Silver Nanoparticle Colloid

    Institute of Scientific and Technical Information of China (English)

    XIE Zhi-Guo; LU Yong-Hua; WANG Pei; LIN Kai-Qun; YAN Jie; MING Hai

    2008-01-01

    @@ A photonic crystal fibre (PCF) surface enhanced Raman scattering (SERS) sensor is developed based on silver nanoparticle colloid.Analyte solution and silver nanoparticles are injected into the air holes of PCF by a simple modified syringe to overcome maes-transport constraints, allowing more silver nanoparticles involved in SERS activity.This sensor offers significant benefit over the conventional SERS sensor with high flexibility, easy manufacture.We demonstrate the detection of 4-mercaptobenzoic acid (4-MBA ) molecules with the injecting way and the common dipping measurement.The injecting way shows obviously better results than the dipping one.Theoretical analysis indicates that this PCF SERS substrate offers enhancement of about 7 orders of magnitude in SERS active area.

  10. Recrystallization and zone melting of charged colloids by thermally induced crystallization.

    Science.gov (United States)

    Shinohara, Mariko; Toyotama, Akiko; Suzuki, Misaki; Sugao, Yukihiro; Okuzono, Tohru; Uchida, Fumio; Yamanaka, Junpei

    2013-08-06

    We examined the application of recrystallization and zone-melting crystallization methods, which have been used widely to fabricate large, high-purity crystals of atomic and molecular systems, to charged colloidal crystals. Our samples were aqueous dispersions of colloidal silica (with particle diameters of d = 108 or 121 nm and particle volume fractions of ϕ = 0.035-0.05) containing the weak base pyridine. The samples crystallized upon heating because of increases in the particle charge numbers, and they melted reversibly on cooling. During the recrystallization experiments, the polycrystalline colloids were partially melted in a Peltier cooling device and then were crystallized by stopping the cooling and allowing the system to return to ambient temperature. The zone-melting crystallization was carried out by melting a narrow zone (millimeter-sized in width) of the polycrystalline colloid samples and then moving the sample slowly over a cooling device to recrystallize the molten region. Using both methods, we fabricated a few centimeter-sized crystals, starting from millimeter-sized original polycrystals when the crystallization rates were sufficiently slow (33 μm/s). Furthermore, the optical quality of the colloidal crystals, such as the half-band widths of the diffraction peaks, was significantly improved. These methods were also useful for refining. Small amounts of impurity particles (fluorescent polystyrene particles, d = 333 nm, ϕ = 5 × 10(-5)), added to the colloidal crystals, were excluded from the crystals when the crystallization rates were sufficiently slow (∼0.1 μm/s). We expect that the present findings will be useful for fabricating large, high-purity colloidal crystals.

  11. 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.

  12. Hierarchical opal grating films prepared by slide coating of colloidal dispersions in binary liquid media.

    Science.gov (United States)

    Lee, Wonmok; Kim, Seulgi; Kim, Seulki; Kim, Jin-Ho; Lee, Hyunjung

    2015-02-15

    There are active researches on well ordered opal films due to their possible applications to various photonic devices. A recently developed slide coating method is capable of rapid fabrication of large area opal films from aqueous colloidal dispersion. In the current study, the slide coating of polystyrene colloidal dispersions in water/i-propanol (IPA) binary media is investigated. Under high IPA content in a dispersing medium, resulting opal film showed a deterioration of long range order, as well as a decreased film thickness due to dilution effect. From the binary liquid, the dried opal films exhibited the unprecedented topological groove patterns with varying periodic distances as a function of alcohol contents in the media. The groove patterns were consisted of the hierarchical structures of the terraced opal layers with periodic thickness variations. The origin of the groove patterns was attributed to a shear-induced periodic instability of colloidal concentration within a thin channel during the coating process which was directly converted to a groove patterns in a resulting opal film due to rapid evaporation of liquid. The groove periods of opal films were in the range of 50-500 μm, and the thickness differences between peak and valley of the groove were significantly large enough to be optically distinguishable, such that the coated films can be utilized as the optical grating film to disperse infra-red light. Utilizing a lowered hydrophilicity of water/IPA dispersant, an opal film could be successfully coated on a flexible Mylar film without significant dewetting problem.

  13. 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...

  14. Colloid-in-Liquid Crystal Gels that Respond to Biomolecular Interactions

    OpenAIRE

    Agarwal, Ankit; Sidiq, Sumyra; Setia, Shilpa; Bukusoglu, Emre; de Pablo, Juan J.; Pal, Santanu Kumar; Abbott, Nicholas L.

    2013-01-01

    This paper advances the design of stimuli-responsive materials based on colloidal particles dispersed in liquid crystals (LCs). Specifically, we report that thin films of colloid-in-liquid crystal (CLC) gels can undergo easily visualized ordering transitions in response to reversible and irreversible (enzymatic) biomolecular interactions occurring at aqueous interfaces of the gels. In particular, we demonstrate that LC ordering transitions can propagate across the entire thickness of the gels...

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

    Science.gov (United States)

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

    2017-01-25

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

  16. Colloidal Photonic Crystals Containing Silver Nanoparticles with Tunable Structural Colors

    Directory of Open Access Journals (Sweden)

    Chun-Feng Lai

    2016-05-01

    Full Text Available Polystyrene (PS colloidal photonic crystals (CPhCs containing silver nanoparticles (AgNPs present tunable structural colors. PS CPhC color films containing a high concentration of AgNPs were prepared using self-assembly process through gravitational sedimentation method. High-concentration AgNPs were deposited on the bottom of the substrate and acted as black materials to absorb background and scattering light. Brilliant structural colors were enhanced because of the absorption of incoherent scattering light, and color saturation was increased by the distribution AgNPs on the PS CPhC surfaces. The vivid iridescent structural colors of AgNPs/PS hybrid CPhC films were based on Bragg diffraction and backward scattering absorption using AgNPs. The photonic stop band of PS CPhCs and AgNPs/PS hybrid CPhCs were measured by UV–visible reflection spectrometry and calculated based on the Bragg–Snell law. In addition, the tunable structural colors of AgNPs/PS hybrid CPhC films were evaluated using color measurements according to the Commission International d’Eclairage standard colorimetric system. This paper presents a simple and inexpensive method to produce tunable structural colors for numerous applications, such as textile fabrics, bionic colors, catalysis, and paints.

  17. 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

  18. 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.

  19. Asymmetrical phase separation and gelation in binary mixtures of oppositely charged colloids

    Science.gov (United States)

    Zong, Yiwu; Yuan, Guangcui; Han, Charles C.

    2016-07-01

    Two types of colloidal particles, which are nearly the same in chemical composition but carry opposite surface charges, are mixed in water. Depending on the relative proportion of the oppositely charged particles, the process of aggregation leads to the formation of discrete clusters of various sizes in dilute dispersions, and to the development of particle gel networks in more concentrated systems. Due to the significant difference in the absolute values of surface charges (negative particle: -48 mV, positive particle: +24 mV), the phase separation and the gelation behaviors are asymmetric with respect to the mixing ratio. Mixtures with excess negative particles are more stable, while mixtures with excess positive particles are easily affected by phase separation. The hetero-aggregation triggered by the addition of microscopically large macro-ions is similar to what is often observed in a mono-component charged colloidal system, i.e., phase separation occurs through addition of small electrolyte ions. Within the concentration region investigated here, it is clear that the gel line is buried inside the phase separation region. Gelation occurs only when the number and size of the clusters are large and big enough to connect up into a space-spanning network. Our results indicate that, in this binary mixture of oppositely charged colloids, although the interaction between unlike species is attractive and that between like species is repulsive, the onset of gelation is in fact governed by the equilibrium phase separation, as in the case of purely attractive systems with short-range isotropic interaction.

  20. Avalanches, plasticity, and ordering in colloidal crystals under compression.

    Science.gov (United States)

    McDermott, D; Reichhardt, C J Olson; Reichhardt, C

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

  1. 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.

  2. Scanning Transmission X-Ray Microscopy as a Novel Tool to Probe Colloidal and Photonic Crystals

    NARCIS (Netherlands)

    van Schooneveld, Matti M.; Hilhorst, Jan; Petukhov, Andrei V.; Tyliszczak, Tolek; Wang, Jian; Weckhuysen, Bert M.; de Groot, Frank M. F.; de Smit, Emiel

    2011-01-01

    Photonic crystals consisting of nano-to micrometer-sized building blocks, such as multiple sorts of colloids, have recently received widespread attention. It remains a challenge, however, to adequately probe the internal crystal structure and the corresponding deformations that inhibit the proper fu

  3. Colloidal nanoparticles trapped by liquid-crystal defect lines: A lattice Monte Carlo simulation

    Science.gov (United States)

    Jose, Regina; Skačej, Gregor; Sastry, V. S. S.; Žumer, Slobodan

    2014-09-01

    Lattice-based Monte Carlo simulations are performed to study a confined liquid crystal system with a topological disclination line entangling a colloidal nanoparticle. In our microscopic study the disclination line is stretched by moving the colloid, as in laser tweezing experiments, which results in a restoring force attempting to minimize the disclination length. From constant-force simulations we extract the corresponding disclination line tension, estimated as ˜50 pN, and observe its decrease with increasing temperature.

  4. 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.

  5. Structural deformations in liquid crystals with dispersed magnetic nano-colloids

    Directory of Open Access Journals (Sweden)

    S Shoarinejad

    2012-06-01

    Full Text Available  The stable colloidal dispersions of magnetic nano-particles in nematic liquid crystals are called ferronematics. Their behaviour in magnetic fields depends on various parameters such as anchoring energy, magnetic anisotropy, and shape and volume fraction of the particles. In the present paper, the threshold field is obtained for these colloidal nematics. Then, the influence of magnetic anisotropy, cell thickness, magnetic moment, and volume fraction of the particles are discussed . It is found that due to the influence of some effective parameters, the threshold field changes when compared to pure nematic liquid crystals. The obtained results are consistent with the reported experimental results.

  6. Shear moduli in bcc-fcc structure transition of colloidal crystals.

    Science.gov (United States)

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Zhu, Ruzeng

    2015-10-14

    Shear moduli variation in the metastable-stable structure transition of charged colloidal crystals was investigated by the combination techniques of torsional resonance spectroscopy and reflection spectrometer. Modulus of the system increases with the proceeding of the transition process and it finally reaches the maximum value at the end of the transition. For colloidal crystals in stable state, the experimental moduli show good consistence with theoretical expectations. However, in the transition process, the moduli are much smaller than theoretical ones and this can be chalked up to crystalline imperfection in the transition state.

  7. Shear moduli in bcc-fcc structure transition of colloidal crystals

    Science.gov (United States)

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Zhu, Ruzeng

    2015-10-01

    Shear moduli variation in the metastable-stable structure transition of charged colloidal crystals was investigated by the combination techniques of torsional resonance spectroscopy and reflection spectrometer. Modulus of the system increases with the proceeding of the transition process and it finally reaches the maximum value at the end of the transition. For colloidal crystals in stable state, the experimental moduli show good consistence with theoretical expectations. However, in the transition process, the moduli are much smaller than theoretical ones and this can be chalked up to crystalline imperfection in the transition state.

  8. Disclination lines at homogeneous and heterogeneous colloids immersed in a chiral liquid crystal.

    Science.gov (United States)

    Melle, Michael; Schlotthauer, Sergej; Hall, Carol K; Diaz-Herrera, Enrique; Schoen, Martin

    2014-08-14

    In the present work we perform Monte Carlo simulations in the isothermal-isobaric ensemble to study defect topologies formed in a cholesteric liquid crystal due to the presence of a spherical colloidal particle. Topological defects arise because of the competition between anchoring at the colloidal surface and the local director. We consider homogeneous colloids with either local homeotropic or planar anchoring to validate our model by comparison with earlier lattice Boltzmann studies. Furthermore, we perform simulations of a colloid in a twisted nematic cell and discuss the difference between induced and intrinsic chirality on the formation of topological defects. We present a simple geometrical argument capable of describing the complex three-dimensional topology of disclination lines evolving near the surface of the colloid. The presence of a Janus colloid in a cholesteric host fluid reveals a rich variety of defect structures. Using the Frank free energy we analyze these defects quantitatively indicating a preferred orientation of the Janus colloid relative to the cholesteric helix.

  9. 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

  10. 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.

  11. Finite particle size drives defect-mediated domain structures in strongly confined colloidal liquid crystals

    Science.gov (United States)

    Gârlea, Ioana C.; Mulder, Pieter; Alvarado, José; Dammone, Oliver; Aarts, Dirk G. A. L.; Lettinga, M. Pavlik; Koenderink, Gijsje H.; Mulder, Bela M.

    2016-06-01

    When liquid crystals are confined to finite volumes, the competition between the surface anchoring imposed by the boundaries and the intrinsic orientational symmetry-breaking of these materials gives rise to a host of intriguing phenomena involving topological defect structures. For synthetic molecular mesogens, like the ones used in liquid-crystal displays, these defect structures are independent of the size of the molecules and well described by continuum theories. In contrast, colloidal systems such as carbon nanotubes and biopolymers have micron-sized lengths, so continuum descriptions are expected to break down under strong confinement conditions. Here, we show, by a combination of computer simulations and experiments with virus particles in tailor-made disk- and annulus-shaped microchambers, that strong confinement of colloidal liquid crystals leads to novel defect-stabilized symmetrical domain structures. These finite-size effects point to a potential for designing optically active microstructures, exploiting the as yet unexplored regime of highly confined liquid crystals.

  12. Unidirectional Wave Propagation in Low-Symmetric Colloidal Photonic-Crystal Heterostructures

    Directory of Open Access Journals (Sweden)

    Vassilios Yannopapas

    2015-03-01

    Full Text Available We show theoretically that photonic crystals consisting of colloidal spheres exhibit unidirectional wave propagation and one-way frequency band gaps without breaking time-reversal symmetry via, e.g., the application of an external magnetic field or the use of nonlinear materials. Namely, photonic crystals with low symmetry such as the monoclinic crystal type considered here as well as with unit cells formed by the heterostructure of different photonic crystals show significant unidirectional electromagnetic response. In particular, we show that the use of scatterers with low refractive-index contrast favors the formation of unidirectional frequency gaps which is the optimal route for achieving unidirectional wave propagation.

  13. Fabrication of Ordered Macroporous CdS and ZnS by Colloidal Crystal Template

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Ordered macroporous semiconductors CdS and ZnS with regular arrays of spherical pores have been fabricated by poly (styrene-acrylic) (PSA) colloidal crystal template. It was found that the exact three-dimensional (3D) structure of the template had been imprinted in the final material.

  14. Symmetry Control of Polymer Colloidal Monolayers and Crystals by Electrophoretic Deposition on Patterned Surfaces

    NARCIS (Netherlands)

    Dziomkina, Nina V.; Hempenius, Mark A.; Vancso, G. Julius

    2005-01-01

    Colloidal crystals with body-centered cubic packing (see Figure) can be fabricated by electrophoretic deposition of charged latex particles onto patterned surfaces. Laser-interference lithography produces SiO2 layers patterned with controlled symmetry that can then be used to control the orientation

  15. Structure and stacking order in crystals of asymmetric dumbbell-like colloids

    NARCIS (Netherlands)

    Pal, Antara; Meijer, Janne-Mieke; Wolters, Joost R.; Kegel, Willem K.; Petukhov, A. V.

    2015-01-01

    The crystalline structure assembled out of charge-stabilized asymmetric dumbbell-like colloidal particles in ethyl alcohol by sedimentation has been probed using small-angle X-ray scattering with microradian resolution. The existence of plastic face-centered cubic crystals was inferred from the obse

  16. Fabricating large two-dimensional single colloidal crystals by doping with active particles

    NARCIS (Netherlands)

    van der Meer, B; Filion, L; Dijkstra, M

    2016-01-01

    Using simulations we explore the behaviour of two-dimensional colloidal (poly)crystals doped with active particles. We show that these active dopants can provide an elegant new route to removing grain boundaries in polycrystals. Specifically, we show that active dopants both generate and are attract

  17. Tuning the Colloidal Crystal Structure of Magnetic Particles by External Field

    NARCIS (Netherlands)

    Pal, Antara; Malik, Vikash; He, Le; Erne, Ben H.; Yin, Yadong; Kegel, Willem K.; Petukhov, A. V.

    2015-01-01

    Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-a

  18. 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.

  19. Two studies of colloidal interactions: electric polarizability and protein crystallization. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Fraden, Seth; Hu, Yue

    2001-08-06

    (I)Electric polarizability. During this grant period, the focus was on five topics concerning electric field effects on colloids. The first topic focuses on electric interactions between charged colloids in the absence of external fields, and the remaining four deal with colloids in the presence of external fields. The topics are (1) calculation of the effect of confinement on the pair-potential between like-charged colloids, (2) experimental determination of the interparticle potential under the conditions of dielectric polarization, (3) measurement of the evolution of structure of ER fluids, (4) synthesis of novel colloids designed for ER studies, and (5) computer modeling of polarization of surface charge. (II) Protein crystallization. Studies of the phase behavior of mixtures of proteins and polymers were initiated. The motivation was to test recent theories that suggested that optimal conditions for protein crystallization could be obtained using such mixtures. Combined light scattering measurements of the virial coefficients and determination of the phase diagram of protein/polymer mixtures revealed that the theoretical picture needs to be substantially modified.

  20. Colloidal properties of biomacromolecular solutions: Towards urate oxidase crystal design

    Science.gov (United States)

    Bonneté, Françoise

    2013-02-01

    Crystallization of biological macromolecules is governed by weak interaction forces, attractive and repulsive. Knowledge of solution properties, via second virial coefficient measurements, makes it possible to select physico-chemical parameters that govern and control phase diagrams and thus to grow crystals for specific applications (bio-crystallography or pharmaceutical processes). We highlight here with urate oxidase a salting-in effect that increases its solubility and the depletion effect of amphiphilic polymer, at a polymer concentration above its cmc, in order to grow diffracting crystals of urate oxidase. These two effects were used to grow crystals for high pressure crystallography and in a purification process.

  1. Three-dimensional dynamic photonic crystal creation by four laser beams interference in colloidal quantum dots

    Science.gov (United States)

    Smirnov, A. M.; Mantsevich, V. N.; Ezhova, K. V.; Tikhonov, I. V.; Dneprovskii, V. S.

    2016-04-01

    We investigate a simple way to create dynamic photonic crystals with different lattice symmetry by interference of four non-coplanar laser beams in colloidal solution of CdSe/ZnS quantum dots (QDs). The formation of dynamic photonic crystal was confirmed by the observed diffraction of the beams that have excited photonic crystal at the angles equal to that calculated for the corresponding three-dimensional lattice (self-diffraction regime). Self-diffraction from an induced 3D transient photonic crystal has been discovered in the case of resonant excitation of the excitons (electron - hole transitions) in CdSe/ZnS QDs (highly absorbing colloidal solution) by powerful beams of mode-locked laser with picosecond pulse duration. Self-diffraction arises for four laser beams intersecting in the cell with colloidal CdSe/ZnS QDs due to the induced 3D dynamic photonic crystal. The physical processes that arise in CdSe/ZnS QDs and are responsible for the observed self-action effects are discussed.

  2. Predicting out-of-Equilibrium Phase Behavior in the Dynamic Self-Assembly of Colloidal Crystals

    Science.gov (United States)

    Swan, James; Sherman, Zachary

    Crystals self-assembled from colloidal particles are useful in an array of well demonstrated applications. During fabrication however, gelation and glassification often leave these materials arrested in defective or disordered metastable states. We show how time-dependent, pulsed interparticle interactions can avoid kinetic barriers and yield well-ordered crystalline domains for a suspension of hard, spherical colloidal particles interacting through short-range attractions. This dynamic self-assembly process is analogous to the flashing Brownian rachet. Although this is an inherently unsteady, out-of-equilibrium process, we can predict its outcome using appropriate time averages of equilibrium equations of state. The predicted phase behavior is tested and validated by examining the fluid/crystal coexistence of such dynamically self-assembling dispersions in Brownian dynamics simulations of sedimentation equilibrium and homogeneous nucleation. We also show that our dynamic self-assembly scheme offers control and tunability over the crystal growth kinetics and can even stabilize nonequilibrium structures.

  3. Post-synthetic Anisotropic Wet-Chemical Etching of Colloidal Sodalite ZIF Crystals

    Science.gov (United States)

    Avci, Civan; Ariñez-Soriano, Javier; Carné-Sánchez, Arnau; Guillerm, Vincent; Carbonell, Carlos; Imaz, Inhar; Maspoch, Daniel

    2016-01-01

    Controlling the shape of metal-organic framework (MOF) crystals is important for understanding their crystallization and useful for myriad applications. However, despite the many advances in shaping of inorganic nanoparticles, post-synthetic shape control of MOFs and, in general, molecular crystals remains embryonic. Herein we report using a simple wet-chemistry process at room temperature to control the anisotropic etching of colloidal ZIF-8 and ZIF-67 crystals. Our work enables uniform reshaping of these porous materials into unprecedented morphologies, including cubic and tetrahedral crystals, and even hollow boxes, via acid-base reaction and subsequent sequestration of leached metal ions. Etching tests on these ZIFs reveal that etching occurs preferentially in the crystallographic directions richer in metal-ligand bonds; that, among these directions, the etching rate tends to be faster on the crystal surfaces of higher dimensionality; and that the etching can be modulated by adjusting the pH of the etchant solution. PMID:26458081

  4. Colloidal crystals with diamond symmetry at optical lengthscales

    Science.gov (United States)

    Wang, Yifan; Jenkins, Ian C.; McGinley, James T.; Sinno, Talid; Crocker, John C.

    2017-02-01

    Future optical materials promise to do for photonics what semiconductors did for electronics, but the challenge has long been in creating the structure they require--a regular, three-dimensional array of transparent microspheres arranged like the atoms in a diamond crystal. Here we demonstrate a simple approach for spontaneously growing double-diamond (or B32) crystals that contain a suitable diamond structure, using DNA to direct the self-assembly process. While diamond symmetry crystals have been grown from much smaller nanoparticles, none of those previous methods suffice for the larger particles needed for photonic applications, whose size must be comparable to the wavelength of visible light. Intriguingly, the crystals we observe do not readily form in previously validated simulations; nor have they been predicted theoretically. This finding suggests that other unexpected microstructures may be accessible using this approach and bodes well for future efforts to inexpensively mass-produce metamaterials for an array of photonic applications.

  5. Colloidal crystals with diamond symmetry at optical lengthscales

    Science.gov (United States)

    Wang, Yifan; Jenkins, Ian C.; McGinley, James T.; Sinno, Talid; Crocker, John C.

    2017-01-01

    Future optical materials promise to do for photonics what semiconductors did for electronics, but the challenge has long been in creating the structure they require—a regular, three-dimensional array of transparent microspheres arranged like the atoms in a diamond crystal. Here we demonstrate a simple approach for spontaneously growing double-diamond (or B32) crystals that contain a suitable diamond structure, using DNA to direct the self-assembly process. While diamond symmetry crystals have been grown from much smaller nanoparticles, none of those previous methods suffice for the larger particles needed for photonic applications, whose size must be comparable to the wavelength of visible light. Intriguingly, the crystals we observe do not readily form in previously validated simulations; nor have they been predicted theoretically. This finding suggests that other unexpected microstructures may be accessible using this approach and bodes well for future efforts to inexpensively mass-produce metamaterials for an array of photonic applications. PMID:28194025

  6. Crystals of Janus colloids at various interaction ranges

    Science.gov (United States)

    Preisler, Z.; Vissers, T.; Smallenburg, F.; Sciortino, F.

    2016-08-01

    We investigate the effect of interaction range on the phase behaviour of Janus particles with a Kern-Frenkel potential. Specifically, we study interaction ranges Δ = 0.1σ, 0.3σ, 0.4σ, 0.5σ with σ the particle diameter, and use variable box shape simulations to predict crystal structures. We found that changing the interaction range beyond 0.2σ drastically increases the variety of possible crystal structures. In addition to close-packed structures, we find body-centered tetragonal and AA-stacked hexagonal crystals, as well as several lamellar crystals. For long interaction ranges and low temperatures, we also observe an extremely large number of metastable structures which compete with the thermodynamically stable ones. These competing structures hinder the detection of the lowest-energy crystal structures, and are also likely to interfere with the spontaneous formation of the ground-state structure. Finally, we determine the gas-liquid coexistence curves for several interaction ranges, and observe that these are metastable with respect to crystallization.

  7. Binary mixtures of rod-like colloids under shear: microscopically-based equilibrium theory and order-parameter dynamics.

    Science.gov (United States)

    Lugo-Frías, Rodrigo; Klapp, Sabine H L

    2016-06-22

    This paper is concerned with the dynamics of a binary mixture of rod-like, repulsive colloidal particles driven out of equilibrium by means of a steady shear flow (Couette geometry). To this end we first derive, starting from a microscopic density functional in Parsons-Lee approximation, a mesoscopic free energy functional whose main variables are the orientational order parameter tensors. Based on this mesoscopic functional we then explore the stability of isotropic and nematic equilibrium phases in terms of composition and rod lengths. Second, by combining the equilibrium theory with the Doi-Hess approach for the order parameter dynamics under shear, we investigate the orientational dynamics of binary mixtures for a range of shear rates and coupling parameters. We find a variety of dynamical states, including synchronized oscillatory states of the two components, but also symmetry breaking behavior where the components display different in-plane oscillatory states.

  8. Self-assembling three-dimensional colloidal photonic crystal multilayers from aqueous ethanol mixture solutions

    Institute of Scientific and Technical Information of China (English)

    Wang Jing; Yuan Chun-Wei; Tang Fang-Qiong

    2005-01-01

    Vertical deposition technique to fabricate thin film solid artificial opals is becoming widely used. In the present work, we report our research on solvent modification and its effect on the quality of colloidal crystals. We used aqueous ethanol mixture solution to replace the ethanol solution, and used the vertical deposition technique to pack the spherical colloids into close-packed arrays. High quality samples can be prepared with thickness up to 20μm in one step. Furthermore, large spheres (diameters greater than 500nm) were successfully crystallized. Scanning electron microscopy (SEM) and optical methods were used to measure sample thickness and uniformity. The number of layers was calculated from the spectral separation of the Fabry-Perot fringes.

  9. Liquid crystals and their interactions with colloidal particles and phospholipid membranes: Molecular simulation studies

    Science.gov (United States)

    Kim, Evelina B.

    Experimentally, liquid crystals (LC) can be used as the basis for optical biomolecular sensors that rely on LC ordering. Recently, the use of LC as a reporting medium has been extended to investigations of molecular scale processes at lipid laden aqueous-LC interfaces and at biological cell membranes. In this thesis, we present two related studies where liquid crystals are modelled at different length scales. We examine (a) the behavior of nanoscopic colloidal particles in LC systems, using Monte Carlo (MC) molecular simulations and a mesoscopic dynamic field theory (DyFT); and (b) specific interactions of two types of mesogens with a model phospholipid bilayer, using atomistic molecular dynamics (MD) at the A-nm scale. In (a), we consider colloidal particles suspended in a LC, confined between two walls. We calculate the colloid-substrate and colloid-colloid potentials of mean force (PMF). For the MC simulations, we developed a new technique (ExEDOS or Expanded Ensemble Density Of States) that ensures good sampling of phase space without prior knowledge of the energy landscape of the system. Both results, simulation and DyFT, indicate a repulsive force acting between a colloid and a wall. In contrast, both techniques indicate an overall colloid-colloid attraction and predict a new topology of the disclination lines that arises when the particles approach each other. In (b), we find that mesogens (pentylcyanobiphenyl [5CB] or difluorophenyl-pentylbicyclohexyl [5CF]) preferentially partition from the aqueous phase into a dipalmitoylphosphatidylcholine (DPPC) bilayer. We find highly favorable free energy differences for partitioning (-18kBT for 5CB, -26k BT for 5CF). We also simulated fully hydrated bilayers with embedded 5CB or 5CF at concentrations used in recent experiments (6 mol% and 20 mol%). The presence of mesogens in the bilayer enhances the order of lipid acyl tails and changes the spatial and orientational arrangement of lipid headgroup atoms. A stronger

  10. 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

  11. Using Two-Dimensional Colloidal Crystals to Understand Crystallography

    Science.gov (United States)

    Bosse, Stephanie A.; Loening, Nikolaus M.

    2008-01-01

    X-ray crystallography is an essential technique for modern chemistry and biochemistry, but it is infrequently encountered by undergraduate students owing to lack of access to equipment, the time-scale for generating diffraction-quality molecular crystals, and the level of mathematics involved in analyzing the resulting diffraction patterns.…

  12. Self-assembly of colloidal particles in deformation landscapes of electrically driven layer undulations in cholesteric liquid crystals

    Science.gov (United States)

    Varney, Michael C. M.; Zhang, Qiaoxuan; Senyuk, Bohdan; Smalyukh, Ivan I.

    2016-10-01

    We study elastic interactions between colloidal particles and deformation landscapes of undulations in a cholesteric liquid crystal under an electric field applied normal to cholesteric layers. The onset of undulation instability is influenced by the presence of colloidal inclusions and, in turn, layers' undulations mediate the spatial patterning of particle locations. We find that the bending of cholesteric layers around a colloidal particle surface prompts the local nucleation of an undulations lattice at electric fields below the well-defined threshold known for liquid crystals without inclusions, and that the onset of the resulting lattice is locally influenced, both dimensionally and orientationally, by the initial arrangements of colloids defined using laser tweezers. Spherical particles tend to spatially localize in the regions of strong distortions of the cholesteric layers, while colloidal nanowires exhibit an additional preference for multistable alignment offset along various vectors of the undulations lattice. Magnetic rotation of superparamagnetic colloidal particles couples with the locally distorted helical axis and undulating cholesteric layers in a manner that allows for a controlled three-dimensional translation of these particles. These interaction modes lend insight into the physics of liquid crystal structure-colloid elastic interactions, as well as point the way towards guided self-assembly of reconfigurable colloidal composites with potential applications in diffraction optics and photonics.

  13. 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.

  14. From colloidal nanoparticles to a single crystal: new insights into the formation of nacre's aragonite tablets.

    Science.gov (United States)

    Zhang, Gangsheng; Xu, Jun

    2013-04-01

    Nacre has long served as a model for understanding the biomineralization mechanism and designing bio-inspired materials. However, its basic building blocks, the aragonite tablets, are still under debate in terms of their fine structure at the nanoscale and corresponding formation mechanism. Here, using a field emission scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), and X-ray diffractometer, we comparatively investigate the immature and mature tablet from the green mussel's nacre. We find that: (1) the early immature tablet consists of closely-packed colloidal nanoparticles, which contain nanocrystals surrounded by the amorphous calcium carbonate (ACC) phase. Moreover, these nanocrystals are generally different in shape, size, and orientation; (2) the immature tablet can grow via oriented attachment besides via transformation of the ACC phase; and (3) with growth, the colloidal nanoparticles gradually increase in crystallinity and size until fully crystallized and fused together, leading to a mature tablet that is a monolithic single crystal of aragonite. Based on these findings, we propose a new model showing how the mature tablet evolves from the primary colloidal ACC nanoparticles. We expect this work will provide new insights into the formation of single crystal biominerals via the amorphous precursor route.

  15. Modulating two-dimensional non-close-packed colloidal crystal arrays by deformable soft lithography.

    Science.gov (United States)

    Li, Xiao; Wang, Tieqiang; Zhang, Junhu; Yan, Xin; Zhang, Xuemin; Zhu, Difu; Li, Wei; Zhang, Xun; Yang, Bai

    2010-02-16

    We report a simple method to fabricate two-dimensional (2D) periodic non-close-packed (ncp) arrays of colloidal microspheres with controllable lattice spacing, lattice structure, and pattern arrangement. This method combines soft lithography technique with controlled deformation of polydimethylsiloxane (PDMS) elastomer to convert 2D hexagonal close-packed (hcp) silica microsphere arrays into ncp ones. Self-assembled 2D hcp microsphere arrays were transferred onto the surface of PDMS stamps using the lift-up technique, and then their lattice spacing and lattice structure could be adjusted by solvent swelling or mechanical stretching of the PDMS stamps. Followed by a modified microcontact printing (microcp) technique, the as-prepared 2D ncp microsphere arrays were transferred onto a flat substrate coated with a thin film of poly(vinyl alcohol) (PVA). After removing the PVA film by calcination, the ncp arrays that fell on the substrate without being disturbed could be lifted up, deformed, and transferred again by another PDMS stamp; therefore, the lattice feature could be changed step by step. Combining isotropic solvent swelling and anisotropic mechanical stretching, it is possible to change hcp colloidal arrays into full dimensional ncp ones in all five 2D Bravais lattices. This deformable soft lithography-based lift-up process can also generate patterned ncp arrays of colloidal crystals, including one-dimensional (1D) microsphere arrays with designed structures. This method affords opportunities and spaces for fabrication of novel and complex structures of 1D and 2D ncp colloidal crystal arrays, and these as-prepared structures can be used as molds for colloidal lithography or prototype models for optical materials.

  16. 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.

  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. Large scale structures in liquid crystal/clay colloids

    Energy Technology Data Exchange (ETDEWEB)

    Duijneveldt, Jeroen S van [School of Chemistry, Cantock' s Close, University of Bristol, Bristol BS8 1TS (United Kingdom); Klein, Susanne [HP Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Leach, Edward [HP Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Pizzey, Claire [School of Chemistry, Cantock' s Close, University of Bristol, Bristol BS8 1TS (United Kingdom); Richardson, Robert M [H H Wills Physics Laboratory, Tyndall Avenue, University of Bristol, Bristol BS8 1TL (United Kingdom)

    2005-04-20

    Suspensions of three different clays in K15, a thermotropic liquid crystal, have been studied by optical microscopy and small angle x-ray scattering. The three clays were claytone AF, a surface treated natural montmorillonite, laponite RD, a synthetic hectorite, and mined sepiolite. The claytone and laponite were sterically stabilized whereas sepiolite formed a relatively stable suspension in K15 without any surface treatment. Micrographs of the different suspensions revealed that all three suspensions contained large scale structures. The nature of these aggregates was investigated using small angle x-ray scattering. For the clays with sheet-like particles, claytone and laponite, the flocs contain a mixture of stacked and single platelets. The basal spacing in the stacks was independent of particle concentration in the suspension and the phase of the solvent. The number of platelets in the stack and their percentage in the suspension varied with concentration and the aspect ratio of the platelets. The lath shaped sepiolite did not show any tendency to organize into ordered structures. Here the aggregates are networks of randomly oriented single rods.

  19. 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

  20. Three-Dimensional Structure and Defects in Colloidal Photonic Crystals Revealed by Tomographic Scanning Transmission X-ray Microscopy

    NARCIS (Netherlands)

    Hilhorst, Jan; van Schooneveld, Matti M.; Wang, Jian; de Smit, Emiel; Tyliszczak, Tolek; Raabe, Joerg; Hitchcock, Adam P.; Obst, Martin; de Groot, Frank M. F.; Petukhov, Andrei V.

    2012-01-01

    Self-assembled colloidal crystals have attracted major attention because of their potential as low-cost three-dimensional (3D) photonic crystals. Although a high degree of perfection is crucial for the properties of these materials, little is known about their exact structure and internal defects. I

  1. Kinetics study of crystallization with the disorder-bcc-fcc phase transition of charged colloidal dispersions.

    Science.gov (United States)

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Du, Xuan; Liu, Lixia

    2011-06-21

    Structure transformation (disorder-bcc-fcc) in charged colloidal dispersions, as a manifestation of the Ostwald's step rule, was confirmed by means of reflection spectrum (RS) measurements in our previous study. By taking advantage of a reflection spectrum containing plenty of information about the crystallization behaviors, time-dependent changes of parameters associated with the crystal structure and composition during the disorder-bcc-fcc transition are reported by treating the data from RS in this article. In addition, Avrami's model is adopted to analyze the transition process and investigate the transition rate. On the basis of the above investigations, associated kinetic features of crystallization with the disorder-bcc-fcc transition are described.

  2. 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

  3. Network formation in colloid-liquid crystal mixtures studied by confocal microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cleaver, J; Poon, W C K [School of Physics and the Collaborative Optical Spectroscopy, Micromanipulation and Imaging Centre (COSMIC), JCMB, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh EH9 3JZ (United Kingdom)

    2004-05-19

    We studied the formation of particle networks in colloid + liquid crystal mixtures cooled below the isotropic-nematic transition temperature by time-resolved laser scanning confocal microscopy. Our observations confirm a recent suggestion that alkane impurities play a crucial role in slowing down the speed of the isotropic-nematic interface. This enables the growing nematic droplets to 'push' particles into increasingly concentrated regions, ultimately resulting in a cellular network solid. We also found that faster cooling rates resulted in increasingly hierarchical cellular structures.

  4. Protective colloids and polylactic acid co-affecting the polymorphic crystal forms and crystallinity of indomethacin encapsulated in microspheres.

    Science.gov (United States)

    Lin, S Y; Chen, K S; Teng, H H

    1999-01-01

    The co-effect of protective colloids and polylactic acid (PLA) on the polymorphic crystal forms and crystallinity of indomethacin (IMC) in IMC-loaded PLA microspheres was investigated with differential scanning calorimetry, infrared spectroscopy and x-ray diffractometry, to evaluate the polymorphic crystal forms and crystallinity of IMC encapsulated in PLA microspheres. The surfactant, sodium dodecyl sulphate (SDS), was also used as a dispersing agent. The results indicate that the polymorphism and crystallinity of IMC encapsulated in IMC-loaded PLA microspheres was dependent on the type of protective colloid and PLA used. The amorphous state and alpha-form of IMC were found in the IMC-loaded PLA microspheres prepared using polysaccharide (pectin or beta-cyclodextrin) as a protective colloid or SDS as a dispersing agent. However, the amorphous and methylene chloride solvate of IMC seemed to exist in the IMC-loaded PLA microspheres prepared with the proteins (gelatin or albumin), synthetic cellulose derivative (methyl cellulose or hydroxylpropyl methylcellulose) or the synthetic nonionic polymer (polyvinyl alcohol, polyvinyl pyrrolidone or biosoluble polymer) as a protective colloid. PLA was found to express a certain crystallinity in microspheres and not be affected by the protective colloids, but it played a more important role in influencing the crystallization of IMC during microencapsulation than the protective colloids. No interaction occurred in the physical mixture of IMC and PLA, nor in the IMC-loaded PLA microspheres.

  5. 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.

  6. 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.

  7. Colloidal crystal based plasma polymer patterning to control Pseudomonas aeruginosa attachment to surfaces.

    Science.gov (United States)

    Pingle, Hitesh; Wang, Peng-Yuan; Thissen, Helmut; McArthur, Sally; Kingshott, Peter

    2015-12-02

    Biofilm formation on medical implants and subsequent infections are a global problem. A great deal of effort has focused on developing chemical contrasts based on micro- and nanopatterning for studying and controlling cells and bacteria at surfaces. It has been known that micro- and nanopatterns on surfaces can influence biomolecule adsorption, and subsequent cell and bacterial adhesion. However, less focus has been on precisely controlling patterns to study the initial bacterial attachment mechanisms and subsequently how the patterning influences the role played by biomolecular adsorption on biofilm formation. In this work, the authors have used colloidal self-assembly in a confined area to pattern surfaces with colloidal crystals and used them as masks during allylamine plasma polymer (AAMpp) deposition to generate highly ordered patterns from the micro- to the nanoscale. Polyethylene glycol (PEG)-aldehyde was grafted to the plasma regions via "cloud point" grafting to prevent the attachment of bacteria on the plasma patterned surface regions, thereby controlling the adhesive sites by choice of the colloidal crystal morphology. Pseudomonas aeruginosa was chosen to study the bacterial interactions with these chemically patterned surfaces. Scanning electron microscope, x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and epifluorescence microscopy were used for pattern characterization, surface chemical analysis, and imaging of attached bacteria. The AAMpp influenced bacterial attachment because of the amine groups displaying a positive charge. XPS results confirm the successful grafting of PEG on the AAMpp surfaces. The results showed that PEG patterns can be used as a surface for bacterial patterning including investigating the role of biomolecular patterning on bacterial attachment. These types of patterns are easy to fabricate and could be useful in further applications in biomedical research.

  8. Two-stage crystallization of charged colloids under low supersaturation conditions.

    Science.gov (United States)

    Kratzer, Kai; Arnold, Axel

    2015-03-21

    We report simulations on the homogeneous liquid-fcc nucleation of charged colloids for both low and high contact energy values. As a precursor for crystal formation, we observe increased local order at the position where the crystal will form, but no correlations with the local density. Thus, the nucleation is driven by order fluctuations rather than density fluctuations. Our results also show that the transition involves two stages in both cases, first a transition of liquid → bcc, followed by a bcc → hcp/fcc transition. Both transitions have to overcome free energy barriers, so that a spherical bcc-like cluster is formed first, in which the final fcc structure is nucleated mainly at the surface of the crystallite. This means that the second stage bcc-fcc phase transition is a heterogeneous nucleation in the partially grown solid phase, even though we start from a homogeneous bulk liquid. The height of the bcc → hcp/fcc free energy barrier strongly depends on the contact energies of the colloids. For low contact energy this barrier is low, so that the bcc → hcp/fcc transition occurs spontaneously. For the higher contact energy, the second barrier is too high to be crossed spontaneously by the colloidal system. However, it was possible to ratchet the system over the second barrier and to transform the bcc nuclei into the stable hcp/fcc phase. The transitions are dominated by the first liquid-bcc transition and can be described by classical nucleation theory using an effective surface tension.

  9. Colloid-in-liquid crystal gels that respond to biomolecular interactions.

    Science.gov (United States)

    Agarwal, Ankit; Sidiq, Sumyra; Setia, Shilpa; Bukusoglu, Emre; de Pablo, Juan J; Pal, Santanu Kumar; Abbott, Nicholas L

    2013-08-26

    This paper advances the design of stimuli-responsive materials based on colloidal particles dispersed in liquid crystals (LCs). Specifically, thin films of colloid-in-liquid crystal (CLC) gels undergo easily visualized ordering transitions in response to reversible and irreversible (enzymatic) biomolecular interactions occurring at the aqueous interfaces of the gels. In particular, LC ordering transitions can propagate across the entire thickness of the gels. However, confinement of the LC to small domains with lateral sizes of ∼10 μm does change the nature of the anchoring transitions, as compared to films of pure LC, due to the effects of confinement on the elastic energy stored in the LC. The effects of confinement are also observed to cause the response of individual domains of the LC within the CLC gel to vary significantly from one to another, indicating that manipulation of LC domain size and shape can provide the basis of a general and facile method to tune the response of these LC-based physical gels to interfacial phenomena. Overall, the results presented in this paper establish that CLC gels offer a promising approach to the preparation of self-supporting, LC-based stimuli-responsive materials.

  10. Crystals, colloids, or molecules?: Early controversies about the origin of life and synthetic life.

    Science.gov (United States)

    Deichmann, Ute

    2012-01-01

    Crystals, colloids, and (macro-)molecules have played major roles in theoretical concepts and experimental approaches concerning the generation of life from the mid-19th century on. The notion of the crystallization of life out of a nonliving fluid, a special case of the doctrine of spontaneous generation, was most prominently incorporated into Schleiden's and Schwann's version of cell theory. Refutation at the end of the 19th century of spontaneous generation of life and cells, in particular by Pasteur, Remak, and Virchow, not only gave rise to the flourishing fields of microbiology and cytology, but it also opened up research on synthetic life. These approaches focused on growth and form and colloidal chemistry on the one hand, and on the specificity of organisms' macromolecules and chemical reactions on the other. This article analyzes the contribution of these approaches to synthetic life research and argues that researchers' philosophical predilections and basic beliefs have played important roles in the choice of experimental and theoretical approaches towards synthetic life.

  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. 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

  13. Visual detection of 2,4,6-trinitrotolune by molecularly imprinted colloidal array photonic crystal.

    Science.gov (United States)

    Lu, Wei; Asher, Sanford A; Meng, Zihui; Yan, Zequn; Xue, Min; Qiu, Lili; Yi, Da

    2016-10-05

    We developed a photonic crystal (PhC) sensor for the quantification of 2,4,6-trinitrotoluene (TNT) in solution. Monodisperse (210nm in diameter) molecularly imprinted colloidal particles (MICs) for TNT were prepared by the emulsion polymerization of methyl methacrylate and acrylamide in the presence of TNT as a template. The MICs were then self-assembled into close-packed opal PhC films. The adsorption capacity of the MICs for TNT was 64mg TNT/g. The diffraction from the PhC depended on the TNT concentration in a methanol/water (3/2, v/v) potassium dihydrogen phosphate buffer solution (pH=7.0, 30mM). The limit of detection (LOD) of the sensor was 1.03μg. The color of the molecularly imprinted colloidal array (MICA) changed from green to red with an 84nm diffraction red shift when the TNT concentration increased to 20mM. The sensor response time was 3min. The PhC sensor was selective for TNT compared to similar compounds such as 2,4,6-trinitrophenol, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2-nitromesitylene, 4-nitrotoluene, 2-nitrotoluene, 1,3-dinitrobenzene, methylbenzene, 4-nitrophenol, 2-nitroaniline, 3-aminophenol and 3-nitroaniline. The sensor showed high stability with little response change after three years storage. This sensor technology might be useful for the visual determination of TNT.

  14. Measuring nonlinear stresses generated by defects in 3D colloidal crystals

    CERN Document Server

    Lin, Neil Y C; Schall, Peter; Sethna, James P; Cohen, Itai

    2016-01-01

    The mechanical, structural and functional properties of crystals are determined by their defects and the distribution of stresses surrounding these defects has broad implications for the understanding of transport phenomena. When the defect density rises to levels routinely found in real-world materials, transport is governed by local stresses that are predominantly nonlinear. Such stress fields however, cannot be measured using conventional bulk and local measurement techniques. Here, we report direct and spatially resolved experimental measurements of the nonlinear stresses surrounding colloidal crystalline defect cores, and show that the stresses at vacancy cores generate attractive interactions between them. We also directly visualize the softening of crystalline regions surrounding dislocation cores, and find that stress fluctuations in quiescent polycrystals are uniformly distributed rather than localized at grain boundaries, as is the case in strained atomic polycrystals. Nonlinear stress measurements ...

  15. A novel real space scattering theory: efficient characterization of colloidal crystals

    Energy Technology Data Exchange (ETDEWEB)

    Cabrillo, C; Capitan, M J [Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain); Enciso, E; Cabanas, A [Facultad de Ciencias Quimicas, Departamento de Quimica Fisica I, Universidad Complutense, E-28040, Madrid (Spain); Torralvo, M J [Facultad de Ciencias QuImicas, Departamento de Quimica Inorganica, Universidad Complutense, E-28040, Madrid (Spain); Alvarez, J [Departamento de Fisica de la Materia Condensada, Facultad de Ciencias, Universidad Autonoma de Madrid, Fco. Tomas y Valiente 7, E-28049, Madrid (Spain); Bermejo, F J, E-mail: ccabrilo@foton0.iem.csic.e [Instituto de Estructura de la Materia, Unidad Asociada CSIC, Facultad de Ciencia y TecnologIa, Universidad del PaIs Vasco / EHU, P. Box 644, E-48080, Bilbao (Spain)

    2010-10-01

    Recent advances in self-organized 3D ordered structures of submicron particles as colloidal crystals demand a precise quantitative characterization of the produced nano-structures. Small angle scattering is the technique of choice for such a task but a comprehensive quantitative modeling of the measurements is far from being straightforward. We have developed a theory based in the pair distances distribution which take into the account orientational, positional and staking disorder as well as finite size effects. We show also how the radial scattering length density of the constituent particles, essential for a comprehensive modeling of the experimental data, can be estimated from the position of the form factor local minima. The results reduce to sums of analytical functions over the distribution of pair distances and as such, are suitable for easy (automatic) parallelization.

  16. Controllable fabrication of 2D colloidal-crystal films with polystyrene nanospheres of various diameters by spin-coating

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Jian; Dong, Peitao [College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha, Hunan, 410073 (China); State Key Laboratory of Transducer Technology, Chinese Academy of Science (China); Di, Di; Wang, Chaoguang; Wang, Haoxu; Wang, Junfeng [College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha, Hunan, 410073 (China); Wu, Xuezhong, E-mail: xzwu@nudt.edu.cn [College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha, Hunan, 410073 (China)

    2013-04-01

    Monolayer and bilayer colloidal-crystal films are used as physical mask in nanosphere lithography (NSL). So far, spin-coating experiments have mainly been designed to form nanosphere monolayer with one given size or obtain small areas of polystyrene (PS) nanosphere monolayer which limited the application of these films used as physical masks. The development of NSL required more study focused on the preparation of colloidal-crystal films with large-scale, high ordering degree and nanospheres of different diameters. In this study, PS nanospheres were self-assembled to form monolayer and bilayer colloidal-crystal films by employing spin-coating technology. Based on our experiments, we have built an experiment system of PS nanospheres of certain size ranging from 200 nm to 1300 nm. To give an instance, we have chosen PS nanospheres of four diameters (223 nm, 347 nm, 509 nm, 1300 nm) to fabricate colloidal-crystal films by adjusting the spin speed and acceleration, and we have investigated the relationship between the monolayer coverage areas and spin parameters by designing different spin speed and acceleration for 509 nm nanosphere. Results revealed that monolayer and bilayer films of PS nanospheres with four different diameters were prepared successfully and the single structure where PS nanospheres were in hexagonal close-packed (HCP) order dominated the surface morphologies of both monolayer and bilayer colloidal-crystal films. For 509 nm PS nanosphere, as the spin speed and acceleration increasing, the monolayer coverage areas increase firstly then decrease and at spin speed 1750 rpm and acceleration 600 rpm/s, the areas reaches the biggest.

  17. Activating photonic crystal membrane nanocavities by infiltrating with liquid crystals or luminescent colloidal nanocrystals

    NARCIS (Netherlands)

    Dündar, M.A.; Christova, C.; Silov, A.Y.; Karouta, F.; Nötzel, R.; Wienk, M.; Salemink, H.; Van der Heijden, R.W.

    2010-01-01

    Liquid crystal (LC, Merk 5 CB) is infiltrated into active, InAs quantum dots embedded, InGaAsP membrane type nanocavities to investigate the possible effect of the LC orientation on active cavity tuning. The tuning is demonstrated thermally and thermo-optically. The thermal tuning showed that the ca

  18. Activating photonic crystal membrane nanocavities by infiltrating with liquid crystals or luminescent colloidal nanocrystals

    NARCIS (Netherlands)

    Dündar, M.A.; Christova, C.; Silov, A.Y.; Karouta, F.; Nötzel, R.; Wienk, M.; Salemink, H.; Van der Heijden, R.

    2010-01-01

    Liquid crystal (LC, Merk 5 CB) is infiltrated into active, InAs quantum dots embedded, InGaAsP membrane type nanocavities to investigate the possible effect of the LC orientation on active cavity tuning. The tuning is demonstrated thermally and thermo-optically. The thermal tuning showed that the c

  19. Azeotropic binary solvent mixtures for preparation of organic single crystals

    NARCIS (Netherlands)

    Li, X.; Kjellander, B.K.C.; Anthony, J.E.; Bastiaansen, C.W.M.; Broer, D.J.; Gelinck, G.H.

    2009-01-01

    Here, a new approach is introduced to prepare large single crystals of π-conjugated organic molecules from solution. Utilizing the concept of azeotropism, single crystals of tri-isopropylsilylethynyl pentacene (TIPS-PEN) with dimensions up to millimeters are facilely self-assembled from homogeneous

  20. PHASE ANALYSIS AND CRYSTAL STRUCTURE STUDIES ON BINARY ALLOYS OF ALUMINUM WITH TRANSITION METALS.

    Science.gov (United States)

    In order to provide the necessary background for detailed crystal-chemistry studies in the field of binary aluminum - transition metal systems, extensive investigations have been carried out on the phase relations of a large number of such systems. The results of these studies are briefly summarized, as are also the results of crystal structure determinations of a few alumi num - transition metal phases. (Author)

  1. Towards vibrational spectroscopy on surface-attached colloids performed with a quartz crystal microbalance

    Directory of Open Access Journals (Sweden)

    Diethelm Johannsmann

    2016-12-01

    Full Text Available Colloidal spheres attached to a quartz crystal microbalance (QCM produce the so-called “coupled resonances”. They are resonators of their own, characterized by a particle resonance frequency, a resonance bandwidth, and a modal mass. When the frequency of the main resonator comes close to the frequency of the coupled resonance, the bandwidth goes through a maximum. A coupled resonance can be viewed as an absorption line in acoustic shear-wave spectroscopy. The known concepts from spectroscopy apply. This includes the mode assignment problem, selection rules, and the oscillator strength. In this work, the mode assignment problem was addressed with Finite Element calculations. These reveal that a rigid sphere in contact with a QCM displays two modes of vibration, termed “slipping” and “rocking”. In the slipping mode, the sphere rotates about its center; it exerts a tangential force onto the resonator surface at the point of contact. In the rocking mode, the sphere rotates about the point of contact; it exerts a torque onto the substrate. In liquids, both axes of rotation are slightly displaced from their ideal positions. Characteristic for spectroscopy, the two modes do not couple to the mechanical excitation equally well. The degree of coupling is quantified by an oscillator strength. Because the rocking mode mostly exerts a torque (rather than a tangential force, its coupling to the resonator's tangential motion is weak; the oscillator strength consequently is small. Recent experiments on surface-adsorbed colloidal spheres can be explained by the mode of vibration being of the rocking type.

  2. Nanoassembly of Polydisperse Photonic Crystals based on Binary and Ternary Polymer Opal Alloys

    CERN Document Server

    Zhao, Qibin; Schafer, Christian; Spahn, Peter; Gallei, Markus; Herrmann, Lars; Petukhov, Andrei; Baumberg, Jeremy J

    2016-01-01

    Ordered binary and ternary photonic crystals, composed of different sized polymer-composite spheres with diameter ratios up to 120%, are generated using bending induced oscillatory shearing (BIOS). This viscoelastic system creates polydisperse equilibrium structures, producing mixed opaline colored films with greatly reduced requirements for particle monodispersity, and very different sphere size ratios, compared to other methods of nano-assembly.

  3. Light-induced changes of the refractive indices in a colloid of gold nanoparticles in a nematic liquid crystal.

    Science.gov (United States)

    Lysenko, D; Ouskova, E; Ksondzyk, S; Reshetnyak, V; Cseh, L; Mehl, G H; Reznikov, Y

    2012-05-01

    It was shown that irradiation of a nematic liquid crystal doped with metal nanoparticles in the visible near the plasmon resonance band led to strong thermal changes of the refractive indices. The effect was studied by recording of dynamic optical gratings in the colloid. Nanoparticles "worked" as effective nano-heaters in a matrix causing the order parameter decrease around the particles. A large nonlinearity parameter (n (2) ≈ 10(-2) cm(2)/kW and fast response (≈ 0.7 ms), with no detectable particles' aggregation and excellent photo- thermo-stability make these colloids potentially attractive nonlinear optical media. Application of a dynamic holography technique allowed measuring the coefficients of thermal conductivity of the liquid crystal along the director k (||) = (0.4 ± 0.02) W m(-1)K(-1) and perpendicular to the director k (⊥) = (0.2 ± 0.01) W m(-1)K(-1).

  4. Anisotropic lattice expansion of three-dimensional colloidal crystals and its impact on hypersonic phonon band gaps.

    Science.gov (United States)

    Wu, Songtao; Zhu, Gaohua; Zhang, Jin S; Banerjee, Debasish; Bass, Jay D; Ling, Chen; Yano, Kazuhisa

    2014-05-21

    We report anisotropic expansion of self-assembled colloidal polystyrene-poly(dimethylsiloxane) crystals and its impact on the phonon band structure at hypersonic frequencies. The structural expansion was achieved by a multistep infiltration-polymerization process. Such a process expands the interplanar lattice distance 17% after 8 cycles whereas the in-plane distance remains unaffected. The variation of hypersonic phonon band structure induced by the anisotropic lattice expansion was recorded by Brillouin measurements. In the sample before expansion, a phononic band gap between 3.7 and 4.4 GHz is observed; after 17% structural expansion, the gap is shifted to a lower frequency between 3.5 and 4.0 GHz. This study offers a facile approach to control the macroscopic structure of colloidal crystals with great potential in designing tunable phononic devices.

  5. Induced smectic phases in phase diagrams of binary nematic liquid crystal mixtures.

    Science.gov (United States)

    Huang, Tsang-Min; McCreary, Kathleen; Garg, Shila; Kyu, Thein

    2011-03-28

    To elucidate induced smectic A and smectic B phases in binary nematic liquid crystal mixtures, a generalized thermodynamic model has been developed in the framework of a combined Flory-Huggins free energy for isotropic mixing, Maier-Saupe free energy for orientational ordering, McMillan free energy for smectic ordering, Chandrasekhar-Clark free energy for hexagonal ordering, and phase field free energy for crystal solidification. Although nematic constituents have no smectic phase, the complexation between these constituent liquid crystal molecules in their mixture resulted in a more stable ordered phase such as smectic A or B phases. Various phase transitions of crystal-smectic, smectic-nematic, and nematic-isotropic phases have been determined by minimizing the above combined free energies with respect to each order parameter of these mesophases. By changing the strengths of anisotropic interaction and hexagonal interaction parameters, the present model captures the induced smectic A or smectic B phases of the binary nematic mixtures. Of particular importance is the fact that the calculated phase diagrams show remarkable agreement with the experimental phase diagrams of binary nematic liquid crystal mixtures involving induced smectic A or induced smectic B phase.

  6. Crystal symmetry breaking and vacancies in colloidal lead chalcogenide quantum dots

    Science.gov (United States)

    Bertolotti, Federica; Dirin, Dmitry N.; Ibáñez, Maria; Krumeich, Frank; Cervellino, Antonio; Frison, Ruggero; Voznyy, Oleksandr; Sargent, Edward H.; Kovalenko, Maksym V.; Guagliardi, Antonietta; Masciocchi, Norberto

    2016-09-01

    Size and shape tunability and low-cost solution processability make colloidal lead chalcogenide quantum dots (QDs) an emerging class of building blocks for innovative photovoltaic, thermoelectric and optoelectronic devices. Lead chalcogenide QDs are known to crystallize in the rock-salt structure, although with very different atomic order and stoichiometry in the core and surface regions; however, there exists no convincing prior identification of how extreme downsizing and surface-induced ligand effects influence structural distortion. Using forefront X-ray scattering techniques and density functional theory calculations, here we have identified that, at sizes below 8 nm, PbS and PbSe QDs undergo a lattice distortion with displacement of the Pb sublattice, driven by ligand-induced tensile strain. The resulting permanent electric dipoles may have implications on the oriented attachment of these QDs. Evidence is found for a Pb-deficient core and, in the as-synthesized QDs, for a rhombic dodecahedral shape with nonpolar {110} facets. On varying the nature of the surface ligands, differences in lattice strains are found.

  7. Two-dimensional colloidal crystal assisted formation of conductive porous gold films with flexible structural controllability.

    Science.gov (United States)

    Lu, Zhicheng; Liu, Chen; Han, Heyou

    2015-01-01

    Two-dimensional (2D) colloidal crystals of polystyrene (PS) particles were used as a structure-controlling template to fabricate conductive Au films with an ordered array of nanoholes. The fabrication mainly involved the functionalization of the supporting substrate with polyelectrolyte (PE) functional layers, self-assembly of Au nanoparticles, and electroless deposition of gold. The self-assembly of Au nanoparticles and electroless deposition of gold were macroscopically monitored using ultraviolet-visible (UV-vis) spectroscopy based on the changes in both the extinction spectra of Au nanoparticles and the optical responses of ordered arrays of PS particles. By scanning electron microscopy (SEM) characterization, it was found that Au nanoparticles were assembled into a film structure with orderly dispersed nanoholes and the deposition of gold was confined to the preformed Au nanoparticle films. During the formation of Au films, PE layer structure, Au nanoparticle size and heating treatment applied to the PS template could influence the structures of conductive porous Au films such as the hole diameter, film thickness, and hole diameter/wall thickness ratio (D/W). In addition, this paper also described electrochemical cyclic voltammetry (CV) employed to demonstrate the porosity of the ultimate Au films.

  8. Mixing effects in the crystallization of supercooled quantum binary liquids

    Energy Technology Data Exchange (ETDEWEB)

    Kühnel, M.; Kalinin, A. [Institut für Kernphysik, J. W. Goethe-Universität, Max-von-Laue-Str. 1, 60438 Frankfurt am Main (Germany); Fernández, J. M.; Tejeda, G.; Moreno, E.; Montero, S. [Laboratory of Molecular Fluid Dynamics, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid (Spain); Tramonto, F.; Galli, D. E. [Laboratorio di Calcolo Parallelo e di Simulazioni di Materia Condensata, Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Nava, M. [Laboratorio di Calcolo Parallelo e di Simulazioni di Materia Condensata, Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Computational Science, Department of Chemistry and Applied Biosciences, ETH Zurich, USI Campus, Via Giuseppe Buffi 13, CH-6900 Lugano (Switzerland); Grisenti, R. E. [Institut für Kernphysik, J. W. Goethe-Universität, Max-von-Laue-Str. 1, 60438 Frankfurt am Main (Germany); GSI - Helmholtzzentrum für Schwerionenforschung, Planckstr. 1, 64291 Darmstadt (Germany)

    2015-08-14

    By means of Raman spectroscopy of liquid microjets, we have investigated the crystallization process of supercooled quantum liquid mixtures composed of parahydrogen (pH{sub 2}) or orthodeuterium (oD{sub 2}) diluted with small amounts of neon. We show that the introduction of the Ne impurities affects the crystallization kinetics in terms of a significant reduction of the measured pH{sub 2} and oD{sub 2} crystal growth rates, similarly to what found in our previous work on supercooled pH{sub 2}-oD{sub 2} liquid mixtures [Kühnel et al., Phys. Rev. B 89, 180201(R) (2014)]. Our experimental results, in combination with path-integral simulations of the supercooled liquid mixtures, suggest in particular a correlation between the measured growth rates and the ratio of the effective particle sizes originating from quantum delocalization effects. We further show that the crystalline structure of the mixtures is also affected to a large extent by the presence of the Ne impurities, which likely initiate the freezing process through the formation of Ne-rich crystallites.

  9. 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.

  10. 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.

  11. Equation of State and Structure of Electrostatic Colloidal Crystals: Osmotic Pressure and Scattering Study

    Science.gov (United States)

    Reus, V.; Belloni, L.; Zemb, T.; Lutterbach, N.; Versmold, H.

    1997-04-01

    Electrostatically stabilized aqueous suspensions of bromopolystyrene particles have been studied by scattering and osmotic pressure measurements. We investigated their structure and the interparticle interactions as a function of the volume fraction at very low salinity of the order of micromole/l. At slow crystallization speed we observe perfect crystals, body centrered cubic crystals by light scattering for volume fractions between 0.04 and 0.7% and face centrered cubic crystals by Ultra Small Angle X ray Scattering (USAXS) for higher volume fractions (2 12%). After shear the crystal displays other structures. At low volume fractions (0.1 0.3%), some reflexions disappear by light scattering whereas a strong diffuse “prepeak" appears before the first Bragg peak for higher concentrations (2 12%) evidenced by USAXS. This “prepeak" can be attributed to defects in the crystal. Osmotic pressures have been measured by difference between the hydrostatic pressure in the solution and in the reservoir separated by an hemipermeable membrane. The experimental data are very well reproduced by the Poisson Boltzmann Cell (PBC) theory which shows that the interaction between particles is purely repulsive. No attractive contribution has been experimentally detected. By calculating the mean square displacement of a particle inside its cage from the eccentric PBC model, we have verified that the Lindemann criterion for the existence of crystals (against melting) is satisfied. This study has allowed to determine the equation of state of an electrostatical colloidal crystal and is equivalent to an ultraprecise force/distance measurement between latex particles since the measured forces are of the order of 10^{-12} N for distances of the order of 4000 Å. Des suspensions aqueuses de particules de bromopolystyrène ont été caractérisées par diffusion de lumière, diffusion de rayons X aux petits angles et par des mesures de pression osmotique. Nous avons ainsi étudié leur

  12. Nanoparticle films and photonic crystal multilayers from colloidally stable, size-controllable zinc and iron oxide nanoparticles.

    Science.gov (United States)

    Redel, Engelbert; Mirtchev, Peter; Huai, Chen; Petrov, Srebri; Ozin, Geoffrey A

    2011-04-26

    We report a facile sol-gel synthesis of colloidally stable Fe(2)O(3) and ZnO nanoparticles in alcoholic solvents, ROH, where R = methyl, ethyl, n-propyl, isopropyl, and tert-butyl. We show that nanoparticles of ZnO (4-42) nm and Fe(2)O(3) (4-38 nm) monotonically increase in size upon increasing the alkyl chain length and branching of the alcohol solvent. These colloidally stable and size-controllable metal oxide nanoparticles enable the formation of high optical quality films and photonic crystal multilayers whose component layer thickness, refractive index, porosity, and surface area are found to scale with the nature of the alcohol. Utility of these colloidally stable nanoparticles is demonstrated by preparation of one-dimensional porous photonic crystals comprising ncZnO/ncWO(3) and ncFe(2)O(3)/ncWO(3) multilayers whose photonic stop band can be tuned by tailoring nanoparticle size. Myriad applications can be envisaged for these nanoparticle films in, for example, heterogeneous catalysis, photocatalysis, electrocatalysis, chemical sensors, and solar cells.

  13. Self-assembly of silica colloidal crystal thin films with tuneable structural colours over a wide visible spectrum

    Science.gov (United States)

    Gao, Weihong; Rigout, Muriel; Owens, Huw

    2016-09-01

    Colloidal crystal (CC) thin films that produce structural colours over a wide visible spectrum have been self-assembled from silica nanoparticles (SNPs) using a natural sedimentation method. A series of colloidal suspensions containing uniform SNPs (207-350 nm) were prepared using the Stöber method. The prepared silica suspensions were directly subjected to natural sedimentation at an elevated temperature. The SNPs were deposited under the force of gravity and self-assembled into an ordered array. The solid CC thin films produced structural colours over a wide visible spectrum from red to violet. Visual inspection and colorimetric measurements indicated that the structural colour of the CC thin film is tuneable by varying the SNPs diameters and the viewing angles. The closely packed face-centred cubic (fcc) structure of the CC thin film was confirmed using SEM imaging and was in agreement with the intense colour observed from the film surface.

  14. EDITORIAL: Colloidal suspensions Colloidal suspensions

    Science.gov (United States)

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

    2011-05-01

    fluid-fluid interface [2]. Together with Remco Tuinier, Henk has recently completed a book in this area which is to appear later this year. A major theme in Henk's research is that of phase transitions in lyotropic liquid crystals. Henk, together with Daan Frenkel and Alain Stroobants, realized in the 1980s that a smectic phase in dispersions of rod-like particles can be stable without the presence of attractive interactions, similar to nematic ordering as predicted earlier by Onsager [3]. Together with Gert-Jan Vroege he wrote a seminal review in this area [4]. Henk once said that 'one can only truly develop one colloidal model system in one's career' and in his case this must be that of gibbsite platelets. Initially Henk's group pursued another polymorph of aluminium hydroxide, boehmite, which forms rod-like particles [5], which already displayed nematic liquid crystal phases. The real breakthrough came when the same precursors treated the produced gibbsite platelets slightly differently. These reliably form a discotic nematic phase [6] and, despite the polydispersity in their diameter, a columnar phase [7]. A theme encompassing a wide range of soft matter systems is that of colloidal dynamics and phase transition kinetics. Many colloidal systems have a tendency to get stuck in metastable states, such as gels or glasses. This is a nuisance if one wishes to study phase transitions, but it is of great practical significance. Such issues feature in many of Henk's publications, and with Valerie Anderson he wrote a highly cited review in this area [8]. Henk Lekkerkerker has also invested significant effort into the promotion of synchrotron radiation studies of colloidal suspensions. He was one of the great supporters of the Dutch-Belgian beamline 'DUBBLE' project at the ESRF [9]. He attended one of the very first experiments in Grenoble in 1999, which led to a Nature publication [7]. He was strongly involved in many other experiments which followed and also has been a

  15. Photoinduced electron transfer and interfacial photocatalysis behaviour of ZnS/CdS binary co-colloid system

    Institute of Scientific and Technical Information of China (English)

    陈德文; 刘延秋; 田秋; 徐广智

    1999-01-01

    The interfacial photoinduced electron transfer and related secondary photochemical behaviour in the system of ZnS/CdS co-colloid superfine particles were studied by means of ESR and fluorescence spectroscopy techniques. The photoinduced charge-separation and the radical intermediates produced in the secondary redox reactions initiated via charge separation, as well as the mechanism of reaction processes, were investigated in detail through simultaneous excitation of two colloid components or only one of them. Research results indicated that, as Eg(ZnS)>Eλ>Eg(CdS), only CdS in co-colloid system might be excited. The transfer process of electron from the conduction band of CdS to the conduction band of ZnS is forbidden, and under the excitation wavelength range used, the electron transfer of cocolloid system was impossible, thus the photo redox reactions of the substrate in co-colloid system had no obvious difference from those reactions happening in single colloid system. While the excitation wav

  16. Electroluminescence in Potassium Iodide Single Crystals Containing Potassium Metal Colloids (VII) -Theory of the Frequency Dependence of the Threshold a.c. Electric Field-

    OpenAIRE

    HAGIHARA, Takeshi; HAYASHIUCHI, Yoshihiro

    1996-01-01

    Electroluminescence(EL) in colored KI single crystals containing potassium metal colloids has been studied theoretically to understand the characteristics of the EL. A simple rate equation is introduced to describe the dynamical change in numbers of both luminescence centers and conduction electrons produced from the potassium metal colloids by external high a.c. electric field excitation. The present model explains well the EL experimental results reported previously, e.g., the frequency dep...

  17. Guided mode extraction in monolayer colloidal crystals based on the phase variation of reflection and transmission coefficients

    Science.gov (United States)

    Nekuee, Seyed Amir Hossein; Akbari, Mahmood; Khavasi, Amin

    2016-04-01

    An accurate and fast method for guided modes extraction in monolayer colloidal crystals and their inverse replicas is presented. These three-dimensional structures are composed of a monolayer of spherical particles that can easily and simply be prepared by self-assembly method in close packed hexagonal lattices. In this work, we describe how the guided modes, even or odd modes and light cone boundary can be easily determined using phase variations of reflection and transmission coefficients. These coefficients are quickly calculated by Fourier modal method. The band structures are obtained for a monolayer of polystyrene particles and two-dimensional TiO2 inverse opal by this proposed method.

  18. Facile Fabrication of Large Area Polystyrene Colloidal Crystal Monolayer via Surfactant-free Langmuir-Blodgett Technique

    Institute of Scientific and Technical Information of China (English)

    RUAN Wei-dong; L(U) Zhi-cheng; JI Nan; WANG Chun-xu; ZHAO Bing; ZHANG Jun-hu

    2007-01-01

    A facile and novel method for the production of a large area of well-ordered polystyrene(PS) colloidal crystal monolayer was established using the surfactant-free Langmuir-Blodgett (LB) technique. The hydrophobic property(film-forming ability) of PS spheres was improved by a thermo-rheology treatment before LB assembly, and a large film was obtained. In contrast to the traditional LB technique, no surfactant was needed in this method, which could eliminate the additional contamination of surfactants in the preparation process and provided the products with versatile applications in nanosphere lithography(NSL) for biosensor, surface plasmon resonance, and surface enhanced Raman spectroscopy.

  19. Synthesis, crystal structure and electronic structure of the binary phase Rh2Cd5

    Science.gov (United States)

    Koley, Biplab; Chatterjee, S.; Jana, Partha P.

    2017-02-01

    A new phase in the Rh-Cd binary system - Rh2Cd5 has been identified and characterized by single crystal X-ray diffraction and Energy dispersive X-ray analysis. The stoichiometric compound Rh2Cd5 crystallizes with a unit cell containing 14 atoms, in the orthorhombic space group Pbam (55). The crystal structure of Rh2Cd5 can be described as a defect form of the In3Pd5 structure with ordered vacancies, formed of two 2D atomic layers with the stacking sequence: ABAB. The A type layers consist of (3.6.3.6)-Kagomé nets of Cd atoms while the B type layers consist of (35) (37)- nets of both Cd and Rh atoms. The stability of this line phase is investigated by first principle electronic structure calculations on the model of ordered Rh2Cd5.

  20. Investigation on Thermal and Optical Properties of Hydrogen-Bonded Binary Liquid Crystals

    Science.gov (United States)

    Ranjeeth kumar, T.; Sundaram, S.; Vasanthi, T.; Subhasri, P.; Chitravel, T.; Senthil, T. S.; Jayaprakasam, R.; Vijayakumar, V. N.

    2016-12-01

    A homologous series of hydrogen-bonded liquid crystals (HBLCs) are synthesized and characterized. Intermolecular hydrogen bonding occurs between 4-methoxycinnamic acid (4MCA) and p-n-alkyloxy benzoic acids (nOBA, where n = 3, 7 to 12). These binary complexes have been obtained by following well-designed synthesis route. The subsequent binary complexes have been characterized by polarizing optical thermal microscopy (POM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The present work explains the details of the association between the mesogenic phase behavior and H-bonding in the homologous series of 4MCA + nOBA. Nematic phase is interrelated with the closed dimers between acid molecules through the formation of strong hydrogen bonds. But, high concentrations are linked to the manifestation of smectic phases that disturb the local order of the nematic phase. As a result, the higher-order mesophases are observed in the present binary complex series. The inclusion of nematic LC (4MCA) in the nOBA alters the melting temperature and the clearing temperature as lower than those of the individual. Also, the wide mesophase regions of the present series are identified compared to those of the constituent mesogens. The optical tilt angle of binary mixtures for smectic C phase and thermal stability factors of the mesogenic phases have been discussed.

  1. Assembly of colloidal strings in a simple fluid flow

    Science.gov (United States)

    Abe, Yu; Francis, Lorraine; Cheng, Xiang

    Colloidal particles self-assemble into ordered structures ranging from face- and body-centered cubic crystals to binary ionic crystals and to kagome lattices. Such diverse micron-scale structures are of practical importance for creating photonic materials and also of fundamental interest for probing equilibrium and non-equilibrium statistical mechanics. As a particularly interesting example, 1D colloidal strings provide a unique system for investigating non-equilibrium dynamics of crystal lattices. Here, we report a simple experimental method for constructing 1D colloidal crystals, where colloidal particles self-assemble into flow-aligned string structures near solid boundary under unidirectional flows. Using fast confocal microscopy, we explore the degree of particle alignment as functions of flow rate, particle concentrations, wetting properties of solid boundary and ionic strength of solvent. Through our systematic experiments, we show that these colloidal strings arise from hydrodynamic coupling, facilitated by electrostatic attractions between particles and the boundary. Compared with previous methods, our work provides a much simpler experimental procedure for assembling a large number of colloidal strings.

  2. Life at ultralow interfacial tension: Wetting, waves and droplets in demixed colloid-polymer mixtures

    NARCIS (Netherlands)

    Lekkerkerker, H.N.W.; de Villeneuve, V.W.A.; de Folter, J.W.J.; Schmidt, M.; Hennequin, Y.; Bonn, D.; Indekeu, J.O.; Aarts, D.G.A.L.

    2008-01-01

    Mixtures of colloids and polymers display a rich phase behavior, involving colloidal gas (rich in polymer, poor in colloid), colloidal liquid (poor in polymer, rich in colloid) and colloidal crystal phases (poor in polymer, highly ordered colloids). Recently, the colloidal gas-colloidal liquid inter

  3. Life at ultralow interfacial tension: wetting, waves and droplets in demixed colloid-polymer mixtures

    NARCIS (Netherlands)

    Lekkerkerker, H.N.W.; de Villeneuve, V.W.A.; de Folter, J.W.J.; Schmidt, M.; Hennequin, Y.; Bonn, D.; Indekeu, J.O.; Aarts, D.G.A.L.

    2008-01-01

    Mixtures of colloids and polymers display a rich phase behavior, involving colloidal gas (rich in polymer, poor in colloid), colloidal liquid (poor in polymer, rich in colloid) and colloidal crystal phases (poor in polymer, highly ordered colloids). Recently, the colloidal gas-colloidal liquid inter

  4. Crystal nucleation in binary hard-sphere mixtures: the effect of order parameter on the cluster composition

    NARCIS (Netherlands)

    Ni, R.; Smallenburg, F.; Filion, L.C.; Dijkstra, M.

    2011-01-01

    We study crystal nucleation in a binary mixture of hard spheres and investigate the composition and size of the (non)critical clusters using Monte Carlo simulations. In order to study nucleation of a crystal phase in computer simulations, a one-dimensional order parameter is usually defined to ident

  5. Depinning and heterogeneous dynamics of colloidal crystal layers under shear flow.

    Science.gov (United States)

    Gerloff, Sascha; Klapp, Sabine H L

    2016-12-01

    Using Brownian dynamics (BD) simulations and an analytical approach we investigate the shear-induced, nonequilibrium dynamics of dense colloidal suspensions confined to a narrow slit-pore. Focusing on situations where the colloids arrange in well-defined layers with solidlike in-plane structure, the confined films display complex, nonlinear behavior such as collective depinning and local transport via density excitations. These phenomena are reminiscent of colloidal monolayers driven over a periodic substrate potential. In order to deepen this connection, we present an effective model that maps the dynamics of the shear-driven colloidal layers to the motion of a single particle driven over an effective substrate potential. This model allows us to estimate the critical shear rate of the depinning transition based on the equilibrium configuration, revealing the impact of important parameters, such as the slit-pore width and the interaction strength. We then turn to heterogeneous systems where a layer of small colloids is sheared with respect to bottom layers of large particles. For these incommensurate systems we find that the particle transport is dominated by density excitations resembling the so-called "kink" solutions of the Frenkel-Kontorova (FK) model. In contrast to the FK model, however, the corresponding "antikinks" do not move.

  6. DNA hybridization and ligation for directed colloidal assembly

    Science.gov (United States)

    Shyr, Margaret

    to the glass surface and the other to the colloids surface. To demonstrate that the DNA ligase can permanently link DNA-tethered surfaces, fluorescent colloids were hybridized into aggregated and ligated: in the control sample, unligated particles were easily redispersed, whereas ligated particles remained aggregated. Since the ligation occurs only in the presence of the hybridizing linker and the ligase cofactors, conventional colloidal assembly via vertical deposition could be used to assemble the DNA-functionalized colloids prior to hybridization and ligation. Using vertical deposition, hybridization, and ligation, a number of DNA functionalized colloid structures were assembled layer-by-layer on DNA functionalized glass substrates. First, we demonstrated that DNA-functionalized polystyrene colloids could be assembled on to DNA tethered glass surfaces under non-hybridizing conditions using vertical deposition. Then the linker DNA and ligase were introduced to ligate the DNA on the colloids to the DNA on the glass surface: post-ligation, the unligated multilayers were removed, leaving behind well-ordered hexagonally close-packed monolayers. Since the unligated side of the colloids was available for assembly and hybridization of another layer of colloids, we assembled a polystyrene colloid multilayer (FCC) of alternating fluorescent dyed ligated colloidal monolayers. We demonstrated that a binary colloidal crystal could be assembled from polystyrene colloids of two diameters to form an AB2-like crystal. Finally, silica and polystyrene colloids were assembled and ligated to form silica-polystyrene binary crystals, which may prove a useful route to open structures by using one set of particles as place holders and etching them away after assembly. Another conventional method of colloidal assembly we pursued was sedimentation via slow centrifugation. The salt requirement for DNA hybridization and ligation made it necessary to use slow salt addition through a dialysis

  7. Transition Temperatures of Thermotropic Liquid Crystals from the Local Binary Gray Level Cooccurrence Matrix

    Directory of Open Access Journals (Sweden)

    S. Sreehari Sastry

    2012-01-01

    Full Text Available This paper presents a method which combines the statistical analysis with texture structural analysis called Local Binary Gray Level Cooccurrence Matrix (LBGLCM to investigate the phase transition temperatures of thermotropic p,n-alkyloxy benzoic acid (nOBA, n=4,6,8,10 and 12 liquid crystals. Textures of the homeotropically aligned liquid crystal compounds are recorded as a function of temperature using polarizing optical microscope attached to the hot stage and high resolution camera. In this method, second-order statistical parameters (contrast, energy, homogeneity, and correlation are extracted from the LBGLCM of the textures. The changes associatedwiththe values of extracted parameters as a function of temperature are a helpful process to identify the phases and phase transition temperatures of the samples. Results obtained from this method have validity and are in good agreement with the literature.

  8. Binary mixtures of hydrogen-bonded ferroelectric liquid crystals. Thermal span enhancement in smectic X* phase

    Energy Technology Data Exchange (ETDEWEB)

    Sangameswari, Gopal; Prabu, Nataraj Pongali Sathya; Madhu Mohan, Mathukumalli Lakshmi Narayana [Bannari Amman Institute of Technology, Sathyamangalam (India). Liquid Crystal Research Laboratory (LCRL)

    2015-07-01

    Thermotropic hydrogen-bonded ferroelectric binary liquid crystal mixtures comprising of N-carbamyl-l-glutamic acid (CGA) and p-n-alkyloxy benzoic acids (BAO) are investigated. Variation in the molar proportion of X and Y (where X=CGA+5BAO and Y=CGA+9BAO, CGA+10BAO, CGA+11BAO, and CGA+12BAO) comprising of four series yielded 36 binary mixtures. Optical and thermal properties of these mixtures are meticulously studied in the present article. In addition to the traditional phases, a novel smectic ordering namely smectic X* is observed in all the four series. The aim of the investigation is to obtain abundance occurrence of smectic X* with a large thermal span, and hence, the proportions of the binary mixtures are so chosen that the prelude task is accomplished. Optical tilt angle in smectic X* and smectic C* phases is experimentally determined, and a theoretical fit is performed. Phase diagrams of the four series are constructed from the data obtained from the differential scanning calorimetry and correlated with the phases recorded by the polarising optical microscope studies. Thermal stability factor and thermal equilibrium are also premeditated.

  9. Large Area 2D and 3D Colloidal Photonic Crystals Fabricated by a Roll-to-Roll Langmuir-Blodgett Method.

    Science.gov (United States)

    Parchine, Mikhail; McGrath, Joe; Bardosova, Maria; Pemble, Martyn E

    2016-06-14

    We present our results on the fabrication of large area colloidal photonic crystals on flexible poly(ethylene terephthalate) (PET) film using a roll-to-roll Langmuir-Blodgett technique. Two-dimensional (2D) and three-dimensional (3D) colloidal photonic crystals from silica nanospheres (250 and 550 nm diameter) with a total area of up to 340 cm(2) have been fabricated in a continuous manner compatible with high volume manufacturing. In addition, the antireflective properties and structural integrity of the films have been enhanced via the use of a second roll-to-roll process, employing a slot-die coating of an optical adhesive over the photonic crystal films. Scanning electron microscopy images, atomic force microscopy images, and UV-vis optical transmission and reflection spectra of the fabricated photonic crystals are analyzed. This analysis confirms the high quality of the 2D and 3D photonic crystals fabricated by the roll-to-roll LB technique. Potential device applications of the large area 2D and 3D colloidal photonic crystals on flexible PET film are briefly reviewed.

  10. Direct-writing colloidal photonic crystal microfluidic chips by inkjet printing for label-free protein detection.

    Science.gov (United States)

    Shen, Weizhi; Li, Mingzhu; Ye, Changqing; Jiang, Lei; Song, Yanlin

    2012-09-07

    Integrating photonic crystals (PC) into microfluidic systems has attracted immense interest for its novel functions. However, it is still a great challenge to fabricate PC microfluidic chips rapidly with complex functions. In this work, a direct-writing colloidal PC microchannel was firstly achieved by inkjet printing and was used for the surface-tension-confined microfluidic immune assay. PC channels with different structure colors have been successfully integrated on one chip. The fabricated chip has the advantages of rapid fabrication, quick fluidic transport and can monitor the fluidic fluxion using the naked eye. Utilizing this PC microfluidic chip, a colorimetric label-free immune assay was realized without nonspecific adsorption interference of the target.

  11. Out-of-equilibrium processes in suspensions of oppositely charged colloids: liquid-to-crystal nucleation and gel formation

    Science.gov (United States)

    Sanz, Eduardo

    2009-03-01

    We study the kinetics of the liquid-to-crystal transformation and of gel formation in colloidal suspensions of oppositely charged particles. We analyse, by means of both computer simulations and experiments, the evolution of a fluid quenched to a state point of the phase diagram where the most stable state is either a homogeneous crystalline solid or a solid phase in contact with a dilute gas. On the one hand, at high temperatures and high packing fractions, close to an ordered-solid/disordered-solid coexistence line, we find that the fluid-to-crystal pathway does not follow the minimum free energy route. On the other hand, a quench to a state point far from the ordered-crystal/disordered-crystal coexistence border is followed by a fluid-to-solid transition through the minimum free energy pathway. At low temperatures and packing fractions we observe that the system undergoes a gas-liquid spinodal decomposition that, at some point, arrests giving rise to a gel-like structure. Both our simulations and experiments suggest that increasing the interaction range favors crystallization over vitrification in gel-like structures. [4pt] In collaboration with Chantal Valeriani, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands and SUPA, School of Physics, University of Edinburgh, JCMB King's Buildings, Mayfield Road, Edinburgh EH9 3JZ, UK; Teun Vissers, Andrea Fortini, Mirjam E. Leunissen, and Alfons van Blaaderen, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University; Daan Frenke, FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands and Department of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW, Cambridge, UK; and Marjolein Dijkstra, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University.

  12. 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.

  13. Band structure of collective modes and effective properties of binary magnonic crystals

    Science.gov (United States)

    Zivieri, R.; Malagò, P.; Giovannini, L.

    2014-11-01

    In this paper a theoretical study of the band structure of collective modes of binary ferromagnetic systems formed by a submicrometric periodic array of cylindrical cobalt nanodots partially or completely embedded into a permalloy ferromagnetic film is performed. The binary ferromagnetic systems studied are two-dimensional periodic, but they can be regarded as three-dimensional, since the magnetization is non uniform also along the z direction due to the contrast between the saturation magnetizations of the two ferromagnetic materials along the thickness. The dynamical matrix method, a finite-difference micromagnetic approach, formulated for studying the dynamics in one-component periodic ferromagnetic systems is generalized to ferromagnetic systems composed by F ferromagnetic materials. It is then applied to investigate the spin dynamics in four periodic binary ferromagnetic systems differing each other for the volume of cobalt dots and for the relative position of cobalt dots within the primitive cell. The dispersion curves of the most representative frequency modes are calculated for each system for an in-plane applied magnetic field perpendicular to the Bloch wave vector. The dependence of the dispersion curves on the cobalt quantity and position is discussed in terms of distribution of effective "surface magnetic charges" at the interface between the two ferromagnetic materials. The metamaterial properties in the propagative regime are also studied (1) by introducing an effective magnetization and effective "surface magnetic charges" (2) by describing the metamaterial wave dispersion of the most representative mode in each system within an effective medium approximation and in the dipole-exchange regime. It is also shown that the interchange between cobalt and permalloy does not necessarily lead to an interchange of the corresponding mode dispersion. Analogously to the case of electromagnetic waves in two-dimensional photonic crystals, the degree of

  14. Re-entrant melting as a design principle for DNA-coated colloids

    Science.gov (United States)

    Angioletti-Uberti, Stefano; Mognetti, Bortolo M.; Frenkel, Daan

    2012-06-01

    Colloids functionalized with DNA hold great promise as building blocks for complex self-assembling structures. However, the practical use of DNA-coated colloids (DNACCs) has been limited by the narrowness of the temperature window where the target structures are both thermodynamically stable and kinetically accessible. Here we propose a strategy to design DNACCs, whereby the colloidal suspensions crystallize on cooling and then melt on further cooling. In a phase diagram with such a re-entrant melting, kinetic trapping of the system in non-target structures should be strongly suppressed. We present model calculations and simulations that show that real DNA sequences exist that should bestow this unusual phase behaviour on suitably functionalized colloidal suspensions. We present our results for binary systems, but the concepts that we develop apply to multicomponent systems and should therefore open the way towards the design of truly complex self-assembling colloidal structures.

  15. Intregrating metallic wiring with three-dimensional polystyrene colloidal crystals using electron-beam lithography and three-dimensional laser lithography

    Science.gov (United States)

    Tian, Yaolan; Isotalo, Tero J.; Konttinen, Mikko P.; Li, Jiawei; Heiskanen, Samuli; Geng, Zhuoran; Maasilta, Ilari J.

    2017-02-01

    We demonstrate a method to fabricate narrow, down to a few micron wide metallic leads on top of a three-dimensional (3D) colloidal crystal self-assembled from polystyrene (PS) nanospheres of diameter 260 nm, using electron-beam lithography. This fabrication is not straightforward due to the fact that PS nanospheres cannot usually survive the harsh chemical treatments required in the development and lift-off steps of electron-beam lithography. We solve this problem by increasing the chemical resistance of the PS nanospheres using an additional electron-beam irradiation step, which allows the spheres to retain their shape and their self-assembled structure, even after baking to a temperature of 160 °C, the exposure to the resist developer and the exposure to acetone, all of which are required for the electron-beam lithography step. Moreover, we show that by depositing an aluminum oxide capping layer on top of the colloidal crystal after the e-beam irradiation, the surface is smooth enough so that continuous metal wiring can be deposited by the electron-beam lithography. Finally, we also demonstrate a way to self-assemble PS colloidal crystals into a microscale container, which was fabricated using direct-write 3D laser-lithography. Metallic wiring was also successfully integrated with the combination of a container structure and a PS colloidal crystal. Our goal is to make a device for studies of thermal transport in 3D phononic crystals, but other phononic or photonic crystal applications could also be envisioned.

  16. Field-induced sublimation in perfect two-dimensional colloidal crystals.

    Science.gov (United States)

    Martínez-Pedrero, F; Benet, J; Rubio, J E F; Sanz, E; Rubio, R G; Ortega, F

    2014-01-01

    Phase transitions in two-dimensional (2D) systems are of considerable fundamental and practical importance. However, the kinetics of these processes are difficult to predict and understand, even in simple systems for which equilibrium states are properly described, owing to the difficulty of studying crystallites with single-particle resolution and free of defects. Here we introduce an alternative method for the sublimation of 2D colloidal crystallites by a sudden induction of repulsive forces between the particles. The sublimation kinetics, studied in real space by microscopy and by computer simulations, shows a scaling behavior that suggests a universal mechanism fundamentally different from the one usually accepted for thermal sublimation. The universal behavior found for the early stages of the process may be useful for understanding the dynamic features of particle systems at liquid interfaces and for designing technological applications without the need of performing extensive experimental studies.

  17. Gels and lyotropic liquid crystals: using an imidazolium-based catanionic surfactant in binary solvents.

    Science.gov (United States)

    Cheng, Ni; Hu, Qiongzheng; Bi, Yanhui; Xu, Wenwen; Gong, Yanjun; Yu, Li

    2014-08-01

    The self-assembly behavior of an imidazolium-based catanionic surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C4mim][C12H25SO4]), was investigated in water-ethylammonium nitrate (EAN) mixed solvents with different volume ratios. It is particular interesting that this simple surfactant could not only form lyotropic liquid crystals (LLC) with multimesophases, i.e., normal hexagonal (H1), lamellar liquid crystal (Lα), and reverse bicontinuous cubic phase (V2), in the water-rich environment but also act as an efficient low-molecular-weight gelator (LMWG) which gelated EAN-abundant binary media in a broad concentration range. The peculiar nanodisk cluster morphology of gels composed of similar bilayer units was first observed. FT-IR spectra and density functional theory (DFT) calculations reveal that strong H bonding and electrostatic interactions between EAN and the headgroups of [C4mim][C12H25SO4] are primarily responsible for gelation. The self-assembled gels displayed excellent mechanical strength and a thermoreversible sol-gel transition. It is for the first time that a rich variety of controllable ordered aggregates could be observed only by simply modulating the concentration of a single imidazolium-based catanionic surfactant or the ratio of mixed solvents. This environmentally friendly system is expected to have broad applications in various fields, such as materials science, drug delivery systems, and supramolecular chemistry.

  18. Fabrication of silica/zinc oxide core-shell colloidal photonic crystals

    Science.gov (United States)

    Ma, Xiying; Shi, Weilin; Yan, Zhijun; Shen, Baoping

    2007-07-01

    We have fabricated three-dimensional ZnO photonic crystals by the self-assembly of SiO2/ZnO core-shell microspheres of diameter 180-220 nm by means of a vertical deposition method. The organized crystals adopt a uniform close-packed hexagonal structure with long-range order and a high filling fraction. They exhibit strong partial photonic band gaps at 565-688 nm in the transmission spectrum and a broadened band edge emission at 383 nm in the photoluminescence spectrum. For comparison with these ZnO photonic crystals, we have also prepared pure silica crystals of the same dimensions. The photonic band gaps of the former have been found to be shifted to a longer wavelength by about 200 nm compared to those of the latter as a result of the higher refractive index of ZnO. This approach provides an efficient, economical alternative means of obtaining other, more complicated photonic crystals.

  19. Silicon photonic crystals doped with colloidally synthesized lead salt semiconductors nanocrystals.

    Science.gov (United States)

    Gutman, Nadav; Armon, Akiva; Shandalov, Michael; Osherov, Anna; Golan, Yuval; Sa'ar, Amir

    2009-06-01

    The fabrication of two-dimensional and three-dimensional silicon photonic crystals doped with lead salt nanocrystals is reported. The silicon based photonic crystals of macro-porous silicon are fabricated by electro-chemical etching via masked silicon wafers with the periodicity along the third dimension is achieved by modulating the anodization current and voltage. The chemical solution deposition technique has been utilized to deposit thin layers of lead salts (PbS and PbSe) nanocrystals into the pores. Infrared transmission measurements revealed a considerable red-shift of the photonic band gap in a good agreement with numerical calculations.

  20. Highly cooperative stress relaxation in two-dimensional soft colloidal crystals

    NARCIS (Netherlands)

    Van Der Meer, Berend; Qi, Weikai; Fokkink, Remco G.; Van Der Gucht, Jasper; Dijkstra, Marjolein; Sprakel, Joris

    2014-01-01

    Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it iswell established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal st

  1. Highly cooperative stress relaxation in two-dimensional soft colloidal crystals

    NARCIS (Netherlands)

    Meer, van der B.; Qi, Weikai; Fokkink, R.G.; Gucht, van der J.; Dijkstra, M.; Sprakel, J.H.B.

    2014-01-01

    Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it is well established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal s

  2. Optical characterization of colloidal crystals based on dissymmetric metal-coated oxide submicrospheres

    Energy Technology Data Exchange (ETDEWEB)

    Portal, S. [FEMAN Group, IN2UB, University of Barcelona, Marti i Franques, 1, E-08028 Barcelona (Spain)], E-mail: sabineportal@hotmail.com; Vallve, M.A. [SOC and SAM Group, IN2UB, University of Barcelona, Marti i Franques, 1, E-08028 Barcelona (Spain); Arteaga, O. [FEMAN Group, IN2UB, University of Barcelona, Marti i Franques, 1, E-08028 Barcelona (Spain); Ignes-Mullol, J. [SOC and SAM Group, IN2UB, University of Barcelona, Marti i Franques, 1, E-08028 Barcelona (Spain); Canillas, A.; Bertran, E. [FEMAN Group, IN2UB, University of Barcelona, Marti i Franques, 1, E-08028 Barcelona (Spain)

    2008-12-01

    We studied the optical properties of a two-dimensional (2D) photonic crystal monolayer made up of silica submicrospheres, partly covered by a metallic coating. The silica particles, synthesized by the Stoeber method, had a diameter of about 300 nm, with little size dispersion. They were deposited on glass in a hexagonal pattern by the Langmuir-Blodgett process. The resulting film consisted of a single monolayer of particles. The final step of sample preparation consisted of depositing a discontinuous gold layer on top of the 2D crystal. In order to evaluate the effects of small compositional and structural changes on the optical properties of the 2D crystal, the gold layer was applied to a thickness of less than 2 nm. Anisotropy in the metallic coating was induced by tilting the deposition angle by 10 deg. from the vertical: a discontinuous layer was obtained on top of the particles, with elongated shapes pointing towards the source of the evaporation. The shape of the particles and the film structure were characterized by scanning electron microscopy. Ellipsometric measurements were performed in transmission mode in order to assess the sample anisotropy, and the plasmon response of the samples was determined by extinction measurements. The original 2D crystal presented unexpected optical and uniaxial anisotropy which was increased by a factor of 2 after gold coating.

  3. Colloidal gelation of oppositely charged particles

    NARCIS (Netherlands)

    Russel, E.; Sprakel, J.H.B.; Kodger, T.E.; Weitz, D.A.

    2012-01-01

    Colloidal gelation has been extensively studied for the case of purely attractive systems, but little is understood about how colloidal gelation is affected by the presence of repulsive interactions. Here we demonstrate the gelation of a binary system of oppositely charged colloids, in which repulsi

  4. Controlling statics and dynamics of colloids by photo-patterned liquid crystals (Conference Presentation)

    Science.gov (United States)

    Lavrentovich, Oleg D.; Peng, Chenhui; Guo, Yubing; Shiyanovskii, Sergij V.; Wei, Qi-Huo

    2016-09-01

    Transport of fluids and particles at the microscale is an important theme both in fundamental and applied science. We demonstrate how an advanced approach to photo-induced alignment of liquid crystals can be used to generate nonlinear electrokinetics. The photoalignment technique is based on irradiation of a photosensitive substrate with light through nanoaperture arrays in metal films. The resulting pattern of surface alignment induces predesigned 2D and 3D distortions of local molecular orientation. In presence of a static electric field, these distortions generate spatial charge and drive electrokinetic flows of the new type, in which the velocities depend on the square of the applied electric field. The patterned liquid crystal electrolyte converts the electric energy into the flows and transport of embedded particles of any type (fluid, solid, gaseous) along a predesigned trajectory, posing no limitation on the electric nature (charge, polarizability) of these particles and interfaces. The patterned liquid crystal electrolyte induces persistent vortices of controllable rotation speed and direction that are quintessential for micro- and nanoscale mixing applications.

  5. Experimental design applied to spin coating of 2D colloidal crystal masks: a relevant method?

    Science.gov (United States)

    Colson, Pierre; Cloots, Rudi; Henrist, Catherine

    2011-11-01

    Monolayers of colloidal spheres are used as masks in nanosphere lithography (NSL) for the selective deposition of nanostructured layers. Several methods exist for the formation of self-organized particle monolayers, among which spin coating appears to be very promising. However, a spin coating process is defined by several parameters like several ramps, rotation speeds, and durations. All parameters influence the spreading and drying of the droplet containing the particles. Moreover, scientists are confronted with the formation of numerous defects in spin coated layers, limiting well-ordered areas to a few micrometers squared. So far, empiricism has mainly ruled the world of nanoparticle self-organization by spin coating, and much of the literature is experimentally based. Therefore, the development of experimental protocols to control the ordering of particles is a major goal for further progress in NSL. We applied experimental design to spin coating, to evaluate the efficiency of this method to extract and model the relationships between the experimental parameters and the degree of ordering in the particles monolayers. A set of experiments was generated by the MODDE software and applied to the spin coating of latex suspension (diameter 490 nm). We calculated the ordering by a homemade image analysis tool. The results of partial least squares (PLS) modeling show that the proposed mathematical model only fits data from strictly monolayers but is not predictive for new sets of parameters. We submitted the data to principal component analysis (PCA) that was able to explain 91% of the results when based on strictly monolayered samples. PCA shows that the ordering was positively correlated to the ramp time and negatively correlated to the first rotation speed. We obtain large defect-free domains with the best set of parameters tested in this study. This protocol leads to areas of 200 μm(2), which has never been reported so far.

  6. Fabrication of high-quality colloidal photonic crystals with sharp band edges for ultrafast all-optical switching

    Institute of Scientific and Technical Information of China (English)

    Feng Tian-Hua; Dai Qiao-Feng; Wu Li-Jun; Guo Qi; Hu Wei; Lan Sheng

    2008-01-01

    Application of the pressure controlled isothermal heating vertical deposition method to the fabrication of colloidal photonic crystals is systematically investigated in this paper. The fabricated samples are characterized by scanning electron microscope and transmission spectrum. High-quality samples with large transmissions in the pass bands and the sharp band edges are obtained and the optimum growth condition is determined. For the best sample, the transmission in the pass bands approaches 0.9 while that in the band gap reaches 0.1. More importantly, the maximum differential transmission as high as 0.1/nm is achieved. In addition, it is found that the number of stacking layers does not increase linearly with concentration of PS spheres in a solution, and a gradual saturation occurs when the concentration of PS spheres exceeds 1.5 wt.%. The uniformity of the fabricated samples is examined by transmission measurements on areas with different sizes. Finally, the tolerance of the fabricated samples to baking was studied.

  7. Binary ionic porphyrin nanosheets: electronic and light-harvesting properties regulated by crystal structure

    Science.gov (United States)

    Tian, Yongming; M. Beavers, Christine; Busani, Tito; Martin, Kathleen E.; Jacobsen, John L.; Mercado, Brandon Q.; Swartzentruber, Brian S.; van Swol, Frank; Medforth, Craig J.; Shelnutt, John A.

    2012-02-01

    Crystalline solids self-assembled from anionic and cationic porphyrins provide a new class of multifunctional optoelectronic micro- and nanomaterials. A 1 : 1 combination of zinc(ii) tetra(4-sulfonatophenyl)porphyrin (ZnTPPS) and tin(iv) tetra(N-methyl-4-pyridiniumyl)porphyrin (SnTNMePyP) gives porphyrin nanosheets with high aspect ratios and varying thickness. The room temperature preparation of the nanosheets has provided the first X-ray crystal structure of a cooperative binary ionic (CBI) solid. The unit cell contains one and one-half molecules of aquo-ZnTPPS4- (an electron donor) and three half molecules of dihydroxy-SnTNMePyP4+ (an electron acceptor). Charge balance in the solid is reached without any non-porphyrinic ions, as previously determined for other CBI nanomaterials by non-crystallographic means. The crystal structure reveals a complicated molecular arrangement with slipped π-π stacking only occurring in isolated dimers of one of the symmetrically unique zinc porphyrins. Consistent with the crystal structure, UV-visible J-aggregate bands indicative of exciton delocalization and extended π-π stacking are not observed. XRD measurements show that the structure of the Zn/Sn nanosheets is distinct from that of Zn/Sn four-leaf clover-like CBI solids reported previously. In contrast with the Zn/Sn clovers that do exhibit J-aggregate bands and are photoconductive, the nanosheets are not photoconductive. Even so, the nanosheets act as light-harvesting structures in an artificial photosynthesis system capable of reducing water to hydrogen but not as efficiently as the Zn/Sn clovers.Crystalline solids self-assembled from anionic and cationic porphyrins provide a new class of multifunctional optoelectronic micro- and nanomaterials. A 1 : 1 combination of zinc(ii) tetra(4-sulfonatophenyl)porphyrin (ZnTPPS) and tin(iv) tetra(N-methyl-4-pyridiniumyl)porphyrin (SnTNMePyP) gives porphyrin nanosheets with high aspect ratios and varying thickness. The room

  8. Fabrication of 3-D Photonic Band Gap Crystals Via Colloidal Self-Assembly

    Science.gov (United States)

    Subramaniam, Girija; Blank, Shannon

    2005-01-01

    The behavior of photons in a Photonic Crystals, PCs, is like that of electrons in a semiconductor in that, it prohibits light propagation over a band of frequencies, called Photonic Band Gap, PBG. Photons cannot exist in these band gaps like the forbidden bands of electrons. Thus, PCs lend themselves as potential candidates for devices based on the gap phenomenon. The popular research on PCs stem from their ability to confine light with minimal losses. Large scale 3-D PCs with a PBG in the visible or near infra red region will make optical transistors and sharp bent optical fibers. Efforts are directed to use PCs for information processing and it is not long before we can have optical integrated circuits in the place of electronic ones.

  9. Adsorption, Desorption, Surface Diffusion, Lattice Defect Formation, and Kink Incorporation Processes of Particles on Growth Interfaces of Colloidal Crystals with Attractive Interactions

    Directory of Open Access Journals (Sweden)

    Yoshihisa Suzuki

    2016-07-01

    Full Text Available Good model systems are required in order to understand crystal growth processes because, in many cases, precise incorporation processes of atoms or molecules cannot be visualized easily at the atomic or molecular level. Using a transmission-type optical microscope, we have successfully observed in situ adsorption, desorption, surface diffusion, lattice defect formation, and kink incorporation of particles on growth interfaces of colloidal crystals of polystyrene particles in aqueous sodium polyacrylate solutions. Precise surface transportation and kink incorporation processes of the particles into the colloidal crystals with attractive interactions were observed in situ at the particle level. In particular, contrary to the conventional expectations, the diffusion of particles along steps around a two-dimensional island of the growth interface was not the main route for kink incorporation. This is probably due to the number of bonds between adsorbed particles and particles in a crystal; the number exceeds the limit at which a particle easily exchanges its position to the adjacent one along the step. We also found novel desorption processes of particles from steps to terraces, attributing them to the assistance of attractive forces from additionally adsorbing particles to the particles on the steps.

  10. Directed self-assembly of spheres into a two-dimensional colloidal crystal by viscoelastic stresses.

    Science.gov (United States)

    Pasquino, Rossana; Snijkers, Frank; Grizzuti, Nino; Vermant, Jan

    2010-03-02

    Ordering induced by shear flow can be used to direct the assembly of particles in suspensions. Flow-induced ordering is determined by the balance between a range of forces, such as direct interparticle, Brownian, and hydrodynamic forces. The latter are modified when dealing with viscoelastic rather than Newtonian matrices. In particular, 1D stringlike structures of spherical particles have been observed to form along the flow direction in shear thinning viscoelastic fluids, a phenomenon not observed in Newtonian fluids at similar particle volume fractions. Here we report on the formation of freestanding crystalline patches in planes parallel to the shearing surfaces. The novel microstructure is formed when particles are suspended in viscoelastic, wormlike micellar solutions and only when the applied shear rate exceeds a critical value. In spite of the very low volume fraction (less than 0.01), particles arrange themselves in 2D crystalline patches along the flow direction. This is a bulk phenomenon because 2D crystals form throughout the whole gap between plates, with the gap thickness being much larger than the particle size. Shear flow may hence be an easy method to drive particles into crystalline order in suspensions with viscoelastic properties. The crystalline structure reported here could be used to design new materials with special mechanical, optical, thermal, or electric properties.

  11. 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; Yunker, Peter; Lohr, Matthew; Gratale, Matthew; Lynch, Matthew; Kodger, Thomas; Piazza, Roberto; Buzzaccaro, Stefano; Cipelletti, Luca; Schall, Peter; Veen, Sandra; Wegdam, Gerhard; Lee, Chand-Soo; Choi, Chang-Hyung; Paul, Anna-Lisa; Ferl, Robert J.; Cohen, Jacob

    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

  12. Transport mechanisms of falling crystals detached from the freezing front during solidification of a hypereutectic binary mixture.

    Science.gov (United States)

    Chakraborty, Suman; Kumar, Aloke

    2005-07-08

    Experiments studying transport phenomena during directional solidification of a hypereutectic binary solution in a top-cooled rectangular cavity are often characterized by the descendence of fragmented solid crystals through the unfrozen fluid. This observation, however, is yet to be fundamentally explained from a theoretical perspective. In this Letter, we propose a new model to describe stochastic dynamics of the falling crystals, which is not only applicable to this specific situation, but also appropriate for a generalized mathematical description of evolution of solid particles in the presence of stochastic fluctuations from the ambience accompanied by the growth or dissolution of crystals. Simulations of the proposed model also show an extremely good agreement between the theoretical predictions and earlier experimental findings.

  13. Thermodynamic perturbation theory for self assembling mixtures of multi - patch colloids and colloids with spherically symmetric attractions

    OpenAIRE

    Marshall, B. D.; Chapman, W G

    2013-01-01

    In this paper we extend our previous theory [B. D. Marshall and W.G. Chapman, J. Chem. Phys. 139, 104904 (2013)] for mixtures of single patch colloids (p colloids) and colloids with spherically symmetric attractions (s colloids) to the case that the p colloids can have multiple patches. The theory is then applied to the case of a binary mixture of bi-functional p colloids which have an A and B type patch and s colloids which are not attracted to other s colloids and are attracted to only patc...

  14. Anion effect on the binary and ternary phase diagrams of chiral medetomidine salts and conglomerate crystal formation.

    Science.gov (United States)

    Choobdari, Ebrahim; Fakhraian, Hossein; Peyrovi, Mohammad Hassan

    2014-03-01

    The binary phase diagrams of hydrogen halides salts of medetomidine (Med.HX, X:Br,I) and hydrogen oxalate salt of medetomidine (Med.Ox) were determined based on thermogravimetric/differential thermal analysis (TGA/DTA) and their crystal structure behavior was confirmed by comparison of the X-ray diffractometry and FT-IR spectroscopy of the racemate and pure enantiomer. All hydrogen halide salts presented racemic compound behavior. Heat of fusion of halides salt of (rac)-medetomidine decreased with ionic radius increase. Eutectic points for Med.HCl (previously reported), Med.HBr, and Med.HI rest were unchanged approximately. The solubility of different enantiomeric mixtures of Med.HBr and Med.HI were measured at 10, 20, and 30°C in 2-propanol showing a solubility increase with ionic radius. A binary phase diagram of Med.Ox shows a racemic conglomerate behavior. The solubility of enantiomeric mixtures of Med.Ox were measured at 10, 20, 30, and 40°C. The ternary phase diagram of Med.Ox in ethanol conforms to a conglomerate crystal forming system, favoring its enantiomeric purification by preferential crystallization.

  15. Phase behaviors of binary mixtures composed of electron-rich and electron-poor triphenylene discotic liquid crystals

    Science.gov (United States)

    An, Lingling; Jing, Min; Xiao, Bo; Bai, Xiao-Yan; Zeng, Qing-Dao; Zhao, Ke-Qing

    2016-09-01

    Disk-like liquid crystals (DLCs) can self-assemble to ordered columnar mesophases and are intriguing one-dimensional organic semiconductors with high charge carrier mobility. To improve their applicable property of mesomorphic temperature ranges, we exploit the binary mixtures of electronic donor-acceptor DLC materials. The electron-rich 2,3,6,7,10,11-hexakis(alkoxy)triphenylenes (C4, C6, C8, C10, C12) and an electron-deficient tetrapentyl triphenylene-2,3,6,10-tetracarboxylate have been prepared and their binary mixtures have been investigated. The mesomorphism of the 1:1 (molar ratio) mixtures has been characterized by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and small angel x-ray scattering (SAXS). The self-assembled monolayer structure of a discogen on a solid-liquid interface has been imaged by the high resolution scanning tunneling microscopy (STM). The match of peripheral chain length has important influence on the mesomorphism of the binary mixtures. Project supported by the National Natural Science Foundation of China (Grant Nos. 51273133 and 51443004).

  16. 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)

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

    Science.gov (United States)

    Geiger, C. A.; Dachs, E.

    2008-12-01

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

  18. Crystal structure of shrimp arginine kinase in binary complex with arginine-a molecular view of the phosphagen precursor binding to the enzyme.

    Science.gov (United States)

    López-Zavala, Alonso A; García-Orozco, Karina D; Carrasco-Miranda, Jesús S; Sugich-Miranda, Rocio; Velázquez-Contreras, Enrique F; Criscitiello, Michael F; Brieba, Luis G; Rudiño-Piñera, Enrique; Sotelo-Mundo, Rogerio R

    2013-12-01

    Arginine kinase (AK) is a key enzyme for energetic balance in invertebrates. Although AK is a well-studied system that provides fast energy to invertebrates using the phosphagen phospho-arginine, the structural details on the AK-arginine binary complex interaction remain unclear. Herein, we determined two crystal structures of the Pacific whiteleg shrimp (Litopenaeus vannamei) arginine kinase, one in binary complex with arginine (LvAK-Arg) and a ternary transition state analog complex (TSAC). We found that the arginine guanidinium group makes ionic contacts with Glu225, Cys271 and a network of ordered water molecules. On the zwitterionic side of the amino acid, the backbone amide nitrogens of Gly64 and Val65 coordinate the arginine carboxylate. Glu314, one of proposed acid-base catalytic residues, did not interact with arginine in the binary complex. This residue is located in the flexible loop 310-320 that covers the active site and only stabilizes in the LvAK-TSAC. This is the first binary complex crystal structure of a guanidine kinase in complex with the guanidine substrate and could give insights into the nature of the early steps of phosphagen biosynthesis.

  19. TATVHL peptide-grafted alginate/poly(γ-glutamic acid) scaffolds with inverted colloidal crystal topology for neuronal differentiation of iPS cells.

    Science.gov (United States)

    Kuo, Yung-Chih; Chung, Chiu-Yen

    2012-12-01

    The neuronal differentiation of induced pluripotent stem (iPS) cells in scaffolding biomaterials is an emerging issue in nervous regeneration and repair. This study presents the production of neuron-lineage cells from iPS cells in inverted colloidal crystal (ICC) scaffolds comprising alginate, poly(γ-glutamic acid) (γ-PGA), and TATVHL peptide. The ability of iPS cells to differentiate toward neurons in the constructs was demonstrated by flow-cytometeric sorting and immunochemical staining. The results revealed that hexagonally arrayed microspheres molded alginate/γ-PGA hydrogel into ICC topology with adequate interconnected pores. An increase in the quantity of surface TATVHL peptide enhanced the atomic ratio of nitrogen and the adhesion efficiency of iPS cells in constructs. However, the effect of TATVHL peptide on the viability of iPS cells was insignificant. The adhesion and viability of iPS cells in ICC constructs was higher than those in freeform ones. TATVHL peptide raised the percentage of β III tubulin-identified cells differentiating from iPS cells, indicating that TATVHL peptide stimulated the neuronal development in alginate/γ-PGA ICC constructs. TATVHL peptide-grafted alginate/γ-PGA ICC scaffolds can be promising for establishing nerve tissue from iPS cells.

  20. 磺化聚苯乙烯胶体晶的红外光谱分析%F THE SULFONATED POLYSTYRENE COLLOIDAL CRYSTALS

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    @@ 单分散乳胶体系可以通过自组装形成有序的胶体晶结构,在窄波段光过滤器[1]、生物医学传感器[2]、智能化学传感器[3] 等领域具有重要的应用价值.最近,人们以此有序结构作为模板,制备了有序孔材料[4~7] .另外,此有序结构在仿生学如模拟蛋白石等有序结构等方面也具有重要意义[8].但是,一般的单分散体系如聚苯乙烯体系所形成的有序结构都属于硬性材料,缺乏对外场的响应特性.此外,微球表面没有功能性基团,很难与其它物质兼容,这使得其作为模板合成其它复合材料的潜力大大降低. ANALYSIS OF FT-IR SPECTRA OF THE SULFONATED POLYSTYRENE COLLOIDAL CRYSTALS

  1. 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.

  2. 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

  3. 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.

  4. Self-Assembling of Colloidal Particles Dispersed in Mixture of Ethanol and Water at the Air-Liquid Interface of Colloidal Suspension at Room Temperature

    Institute of Scientific and Technical Information of China (English)

    WANG Ai-Jun; CHEN Sheng-Li; DONG Peng; ZHOU Qian; YUAN Gui-Mei; SU Gu-Cong

    2009-01-01

    Self-assembling of colloidal particles dispersed in a mixture of ethanol and water at the air-liquid interface of the colloidal suspension at room temperature is investigated,and a method of rapidly assembling colloidal particles is proposed.By this method,a uniform colloidal crystal thin 61m over ten square centimeters in area can be fabricated in 10 min without special facilities and heating the suspension.SEM images and a normal incidence transmission spectrum of the sample show that the colloidal crystal film fabricated by this method is of high quality.In addition,this method is very suitable for fabricating colloidal crystal heterostructures.

  5. 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.

  6. Suspensions of colloidal plates in a nematic liquid crystal: a small angle x-ray scattering study

    Energy Technology Data Exchange (ETDEWEB)

    Pizzey, Claire [School of Chemistry, Cantock' s Close, University of Bristol, Bristol BS8 1TS (United Kingdom); Klein, Susanne [HP Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Leach, Edward [HP Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ (United Kingdom); Duijneveldt, Jeroen S van [School of Chemistry, Cantock' s Close, University of Bristol, Bristol BS8 1TS (United Kingdom); Richardson, Robert M [H H Wills Physics Laboratory, Tyndall Avenue, University of Bristol, Bristol BS8 1TL (United Kingdom)

    2004-04-21

    Suspensions of anisometric particles in the nematic phase of a liquid crystalline host solvent were prepared. We chose Claytone AF, a commercial quaternary ammonium surfactant treated montmorillonite, with an aspect ratio of up to 1:2000, and dimethyldioctadecylammonium bromide treated Laponite, with an aspect ratio of 1:8 as the dispersed particles. K15, a nematogenic compound (also known as 5CB), was the dispersing medium. The suspensions were characterized by small angle x-ray scattering (SAXS). The liquid crystal delaminates the clays well, but the scattering curves from Claytone suspensions have prominent first and second order pseudo Bragg peaks, indicating that stacking of clay plates has occurred. We report a model for fitting SAXS data based on Hosemann's theory for suspensions of plane parallel sheets.

  7. Bonding assembled colloids without loss of colloidal stability

    NARCIS (Netherlands)

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

    2012-01-01

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

  8. 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

  9. The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

    Science.gov (United States)

    Miyoshi, K.; Buckley, D. H.

    1979-01-01

    Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh, and W) in contact with single-crystal silicon carbide riders. Results indicate that the coefficient of friction and groove height (corresponding to the wear volume) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease with an increase in solute content of binary alloys. A separate correlation exists between the solute to iron atomic radius ratio and the decreasing rates of change of coefficient of friction and groove height with increasing solute content. These rates of change are minimum at a solute to iron radius ratio of unity. They increase as the atomic ratio increases or decreases linearly from unity. The correlations indicate that atomic size is an important parameter in controlling friction and wear of alloys.

  10. Final Report: The Impact of Carbonate on Surface Protonation, Electron Transfer and Crystallization Reactions in Iron Oxide Nanoparticles and Colloids

    Energy Technology Data Exchange (ETDEWEB)

    Dixon, David Adams [The University of Alabama

    2013-07-02

    This project addresses key issues of importance in the geochemical behavior of iron oxides and in the geochemical cycling of carbon and iron. For Fe, we are specifically studying the influence of carbonate on electron transfer reactions, solid phase transformations, and the binding of carbonate to reactive sites on the edges of particles. The emphasis on carbonate arises because it is widely present in the natural environment, is known to bind strongly to oxide surfaces, is reactive on the time scales of interest, and has a speciation driven by acid-base reactions. The geochemical behavior of carbonate strongly influences global climate change and CO{sub 2} sequestration technologies. Our goal is to answer key questions with regards to specific site binding, electron transfer reactions, and crystallization reactions of iron oxides that impact both the geochemical cycling of iron and CO{sub 2} species. Our work is focused on the molecular level description of carbonate chemistry in solution including the prediction of isotope fractionation factors. We have also done work on critical atmospheric species.

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

    Directory of Open Access Journals (Sweden)

    Jaime Rodriguez-López

    2015-12-01

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

  12. Encodable multiple-fluorescence CdTe@carbon nanoparticles from nanocrystal/colloidal crystal guest-host ensembles.

    Science.gov (United States)

    Guo, Xin; Wang, Cai-Feng; Mao, Li-Hua; Zhang, Jing; Yu, Zi-Yi; Chen, Su

    2013-04-05

    We report herein the controllable generation of encodable multi-fluorescence CdTe@carbon nanoparticles (CdTe@C NPs) via the pyrolysis of quantum dot/photonic crystal (QD/PC) guest-host ensembles. The precursors of CdTe/poly(styrene-co-glycidylmethacrylate) (PS-co-PGMA) QD/PC guest-host ensembles were initially formed via the assembly of epoxy groups of PCs and carboxyl groups on the surface of CdTe QDs, followed by a pyrolysis process to generate CdTe@C NPs. The as-prepared CdTe@C NPs not only integrate the optical properties for both the carbon and CdTe QD constituents, but also enable an impressive enhancement of the fluorescence lifetime for CdTe QDs. The multifarious fluorescent spectra coding for CdTe@C NPs was further generated through regulating the embedded sizes or concentrations of CdTe QDs and the excitation wavelength, and their applications in DNA detection and luminescent patterns were achieved.

  13. 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.

  14. Low-temperature scanning tunneling microscopy/ultraviolet photoelectron spectroscopy investigation of two-dimensional crystallization of C60: pentacence binary system on Ag(111)

    Science.gov (United States)

    Lin Zhang, Jia; Hong Liang Zhang, Kelvin; Qiang Zhong, Jian; Chao Niu, Tian; Chen, Wei

    2012-02-01

    Atomic scale investigation of temperature-dependent two-dimensional (2 D) crystallization processes of fullerene-C60 on pentacene-covered Ag(111) surface has been carried out by in situ low-temperature scanning tunneling microscopy (LT-STM) experiments. To evaluate the effect of molecule-substrate interfacial interactions on the 2 D crystallization of C60: pentacene binary system, we also carried out the same self-assembly experiments of C60 on monolayer pentacene covered graphite substrate. It is revealed that temperature-dependent structural transition of various ordered C60 nanoassemblies is strongly influenced by the molecule-Ag(111) interfacial interactions, and further mediated by the weak C60-pentacene intermolecular interactions. In situ ultraviolet photoelectron spectroscopy (UPS) has been used to evaluate the nature of the intermolecular interactions between C60 and pentacene films.

  15. 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.

  16. 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

  17. Pattern formation and coarse-graining in two-dimensional colloids driven by multiaxial magnetic fields.

    Science.gov (United States)

    Müller, Kathrin; Osterman, Natan; Babič, Dušan; Likos, Christos N; Dobnikar, Jure; Nikoubashman, Arash

    2014-05-13

    We study the pattern formation in a two-dimensional system of superparamagnetic colloids interacting via spatially coherent induced interactions driven by an external precessing magnetic field. On the pair level, upon changing the opening angle of the external field, the interactions smoothly vary from purely repulsive (opening angle equal to zero) to purely attractive (time-averaged pair interactions at an opening angle of 90°). In the experiments, we observed ordered hexagonal crystals at the repulsive end and coarsening frothlike structures for purely attractive interactions. In both of these limiting cases, the dense colloidal systems can be sufficiently accurately described by assuming pairwise additivity of the interaction potentials. However, for a range of intermediate angles, pronounced many-body depolarization effects compete with the direct induced interactions, resulting in inherently anisotropic effective interactions. Under such conditions, we observed the decay of hexagonal order with the concomitant formation of short chains and percolated networks of chains coexisting with free colloids. In order to describe and investigate these systems theoretically, we developed a coarse-grained model of a binary mixture of patchy and nonpatchy particles with the ratio of patchy and nonpatchy colloids as the order parameter. Combining genetic algorithms with Monte Carlo simulations, we optimized the model parameters and quantitatively reproduced the experimentally observed sequence of colloidal structures. The results offer new insight into the anisotropy induced by the many-body effects. At the same time, they allow for a very efficient description of the system by means of a pairwise-additive Hamiltonian, whereupon the original, one-component system features a two-component mixture of isotropic and patchy colloids.

  18. EDITORIAL: Colloidal dispersions in external fields Colloidal dispersions in external fields

    Science.gov (United States)

    Löwen, Hartmut

    2012-11-01

    Colloidal dispersions have long been proven as pivotal model systems for equilibrium phase transition such as crystallization, melting and liquid-gas phase transition. The last decades have revealed that this is also true for nonequilibrium phenomena. In fact, the fascinating possibility to track the individual trajectories of colloidal particles has greatly advanced our understanding of collective behaviour in classical many-body systems and has helped to reveal the underlying physical principles of glass transition, crystal nucleation, and interfacial dynamics (to name just a few typical nonequilibrium effects). External fields can be used to bring colloids out of equilibrium in a controlled way. Different kinds of external fields can be applied to colloidal dispersions, namely shear flow, electric, magnetic and laser-optical fields, and confinement. Typical research areas can be sketched with the by now traditional complexity diagram (figure 1). The complexity of the colloidal system itself as embodied in statistical degrees of freedom is shown on the x-axis while the complexity of the problem posed, namely bulk, an inhomogeneity in equilibrium, steady state nonequilibrium and full time-dependent nonequilibrium are shown on the y-axis. The different external fields which can be imposed are indicated by the different hatched areas. figure1 Figure 1. Diagram of complexity for colloidal dispersions in external fields: while the x-axis shows the complexity of the system, the y-axis shows the complexity of the problem. Regions which can be accessed by different kinds of external fields are indicated. The arrows indicate recent research directions. Active particles are also indicated with a special complexity of internal degrees of freedom [1]. This collection of papers reflects the scientific programme of the International Conference on Colloidal Dispersions in External Fields III (CODEF III) which took place in Bonn-Bad Godesberg from 20-23 March 2012. This was the

  19. Statics and dynamics of colloidal particles on optical tray arrays

    Energy Technology Data Exchange (ETDEWEB)

    Reichardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia J [Los Alamos National Laboratory

    2009-01-01

    We examine the statics and dynamics of charged colloids interacting with periodic optical trap arrays. In particular we study the regime where more than one colloid is confined in each trap, creating effective dimer, trimer, and higher order states called colloidal molecular crystals. The n-mer states have all effective orientational degree of freedom which can be controlled with an external driving field. In general, the external field causes a polarization effect where the orientation of the n-mers aligns with the external field, similar to liquid crystal systems. Additionally, under a rotating external drive the n-mers can rotate with the drive. In some cases a series of structural transitions in the colloidal crystal states occur in the rotating field due to a competition between the ordering of the colloidal molecular crystals and the polarization effect which orients the n-mers in the direction of the drive. We also show that for some parameters, the n-mers continuously rotate with the drive without witching, that depinning transitions can occur where the colloids jump from well to well, and that there are a number of distinct dynamical transitions between the phases. Finally, we illustrate colloidal orderings at fillings of more than four colloids per trap, indicating that it is possible to create higher order colloidal crystal cluster phases.

  20. Entropically Driven Colloidal Assembly in Emulsions

    Science.gov (United States)

    Lin, Keng-Hui; Lai, Liang-Jie; Chen, Hui

    2007-03-01

    Using the techniques developed by Manoharan [1], we encapsulate small numbers of colloidal microspheres and polymers in oil-in-water emulsion droplets, remove the oil and generate colloidal clusters covered with polymers. We observe two types of arrangement in the clusters. The first kind is the same as the type reported in [1] of which the clusters are formed without polymer. The second kind is the same as the structure reported in [2] of which the clusters are formed by binary colloidal microspheres. The polymers we put in the emulsions induce depletion interactions between colloidal particles. We will show that two types of structures are from the interplay between the depletion interactions and surface tension. [1] Manoharan, Elsesser, Pine, Science 301, 483(2003). [2] Cho et al. JACS 127, 15968 (2005).

  1. Preparation and coloring of magnetic colloidal crystals%磁性胶体晶体的制备与呈色特性

    Institute of Scientific and Technical Information of China (English)

    胡光强; 陈永利; 朱欢; 李龙成; 刘文霞

    2016-01-01

    通过化学合成的方法制备出被表面活性剂聚丙烯酸(PAA)修饰的Fe3O4纳米粒子,并应用透射电子显微镜、X射线衍射、磁强计及傅里叶红外光谱仪对产物进行表征,同时利用FDTD solutions光学软件对产物的呈现性能进行建模仿真。最后通过分析得到制备的胶体产物具有超顺磁性能,粒径均一,在水中具有良好的分散性,粒子分散在水中形成的胶体在外在磁场的作用下能够自组装成液态光子晶体,不同磁场大小的调节下能够呈现不同的结构色,磁场越小,颜色越向着波长大的方向偏移,同时,用软件对胶体粒子仿真得到的呈色特性与实验结果一致。这种光子晶体在结构色印刷、传感器、防伪等各个领域有广泛的应用。%Fe3O4nanoparticles modified by surfactant polyacrylic acid (PAA) were synthesized through chemical method.The products were characterized by transmission electron microscopy(TEM),X-ray diffraction,vibrating sample magnetometers(VSM) and Fourier transform infrared spectroscopy(FTIR Spectrometer),respectively.The modeling and simulation of the chromatic performance of products are realized by optical software FDTD solutions. Product was prepared with superparamagnetism,uniform particle size,good dispersion and high water solubility in aqueous solution. These particles dispersed in water can form colloidal solution which can self-assemble into liquid photonic crystal under magnetic field.The different types of structural color will be showed under the regulations of different intensities of magnetic field. The peak of wave will shift towards the direction of the larger wavelength with decreasing magnetic field. In the meantime,there are the same results in the chromatic performance of products between simulation and experimental method. This kind of photonic crystal has many applications in all kinds of fields,such as structural color printing,sensor and anti-counterfeiting.

  2. RETRACTED: Size-controlled spherical polymer nanoparticles: synthesis with tandem acoustic emulsification followed by soap-free emulsion polymerization and one-step fabrication of colloidal crystal films of various colors.

    Science.gov (United States)

    Hirai, Yuki; Nakabayashi, Koji; Kojima, Maya; Atobe, Mahito

    2014-11-01

    We have developed a novel synthesis method for size-controlled polymer nanoparticles using soap-free emulsion polymerization. This new synthetic method involves sequential ultrasonic irradiation (20kHz→500kHz→1.6MHz→2.4MHz) for acoustic emulsification of a water-insoluble monomer such as methylmethacrylate (MMA) in an aqueous medium, followed by emulsion polymerization in the obtained solution without using any surfactants. The sequential ultrasonication (tandem acoustic emulsification) could provide a clear and stable emulsified solution containing monomer droplets with relatively narrow size distribution in the nanometer range. The subsequent polymerization in this solution yielded size-controlled polymethylmethacrylate (PMMA) nanoparticles and monodisperse PMMA nanoparticles of different sizes. Furthermore, colloidal crystal films could be easily prepared from the as-polymerized nanoparticle solution using the fluidic-cell method. Moreover, we succeeded to modify the structural color of colloidal crystal films by the addition of a small amount of organic solvent to the as-polymerized nanoparticle solution for the fluidic-cell method.

  3. Results From the Physics of Colloids Experiment on ISS

    Science.gov (United States)

    Weitz, David; Bailey, Arthur; Manley, Suliana; Prasad, Vikram; Christianson, Rebecca; Sankaran, Subramanian; Doherty, Michael; Jankovsky, Amy; Lorik, Tibor; Shiley, William

    2002-12-01

    The Physics of Colloids in Space (PCS) experiment was accommodated within International Space Station (ISS) EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack 2 and was remotely operated from early June 2001 until February 2002 from NASA Glenn Research Center's Telescience Support Center (TSC) in Cleveland, Ohio, and from the remote site at Harvard University in Cambridge, Massachusetts. PCS was launched on 4/19/2001 on Space Shuttle STS-100. The experiment was activated on 5/31/2001. The entire experimental setup performed remarkably well, and accomplished 2400 hours of science operations on-orbit. The sophisticated instrumentation in PCS is capable of dynamic and static light scattering from 11 to 169 degrees, Bragg scattering over the range from 10 to 60 degrees, dynamic and static light scattering at low angles from 0.3 to 6.0 degrees, and color imaging. The long duration microgravity environment on the ISS facilitated extended studies on the growth and coarsening characteristics of binary crystals. The de-mixing of the colloid-polymer critical-point sample was also studied as it phase-separated into two phases. Further, aging studies on a col-pol gel, gelation rate studies in extremely low concentration fractal gels over several days, and studies on a glass sample, all provided valuable information. Several exciting and unique aspects of these results are discussed here.

  4. Fabrication of bioinspired nanostructured materials via colloidal self-assembly

    Science.gov (United States)

    Huang, Wei-Han

    ultimate strains than nacre and pure GO paper (also synthesized by filtration). Specifically, it exhibits ˜30 times higher fracture energy than filtrated graphene paper and nacre, ˜100 times tougher than filtrated GO paper. Besides reinforced nanocomposites, we further explored the self-assembly of spherical colloids and the templating nanofabrication of moth-eye-inspired broadband antireflection coatings. Binary crystalline structures can be easily accomplished by spin-coating double-layer nonclose-packed colloidal crystals as templates, followed by colloidal templating. The polymer matrix between self-assembled colloidal crystal has been used as a sacrificial template to define the resulting periodic binary nanostructures, including intercalated arrays of silica spheres and polymer posts, gold nanohole arrays with binary sizes, and dimple-nipple antireflection coatings. The binary-structured antireflection coatings exhibit better antireflective properties than unitary coatings. Natural optical structures and nanocomposites teach us a great deal on how to create high performance artificial materials. The bottom-up technologies developed in this thesis are scalable and compatible with standard industrial processes, promising for manufacturing high-performance materials for the benefits of human beings.

  5. Polymer-dispersed liquid crystal elastomers

    Science.gov (United States)

    Rešetič, Andraž; Milavec, Jerneja; Zupančič, Blaž; Domenici, Valentina; Zalar, Boštjan

    2016-10-01

    The need for mechanical manipulation during the curing of conventional liquid crystal elastomers diminishes their applicability in the field of shape-programmable soft materials and future applications in additive manufacturing. Here we report on polymer-dispersed liquid crystal elastomers, novel composite materials that eliminate this difficulty. Their thermal shape memory anisotropy is imprinted by curing in external magnetic field, providing for conventional moulding of macroscopically sized soft, thermomechanically active elastic objects of general shapes. The binary soft-soft composition of isotropic elastomer matrix, filled with freeze-fracture-fabricated, oriented liquid crystal elastomer microparticles as colloidal inclusions, allows for fine-tuning of thermal morphing behaviour. This is accomplished by adjusting the concentration, spatial distribution and orientation of microparticles or using blends of microparticles with different thermomechanical characteristics. We demonstrate that any Gaussian thermomechanical deformation mode (bend, cup, saddle, left and right twist) of a planar sample, as well as beat-like actuation, is attainable with bilayer microparticle configurations.

  6. Chemical Routes to Colloidal Chalcogenide Nanosheets

    Energy Technology Data Exchange (ETDEWEB)

    Schaak, Raymond

    2015-02-19

    This project sought to develop new low-temperature synthetic pathways to intermetallic and chalcogenide nanostructures and powders, with an emphasis on systems that are relevant to advancing the synthesis, processing, and discovery of superconducting materials. The primary synthetic routes involved solution chemistry methods, and several fundamental synthetic challenges that underpinned the formation of these materials were identified and investigated. Methods for incorporating early transition metals and post transition metals into nanoscale and bulk crystals using low-temperature solution chemistry methods were developed and studied, leading to colloidal nanocrystals of elemental indium, manganese, and germanium, as well as nanocrystalline and bulk intermetallic compounds containing germanium, gallium, tin, indium, zinc, bismuth, and lithium. New chemical tools were developed to help target desired phases in complex binary intermetallic and metal chalcogenide systems that contain multiple stable phases, including direct synthesis methods and chemical routes that permit post-synthetic modification. Several phases that are metastable in bulk systems were targeted, synthesized, and characterized as nanocrystalline solids and bulk powders, including the L12-type intermetallic compounds Au3Fe, Au3Ni, and Au3Co, as well as wurtzite-type MnSe. Methods for accessing crystalline metal borides and carbides using direct solution chemistry methods were also developed, with an emphasis on Ni3B and Ni3C, which revealed useful correlations of composition and magnetic properties. Methods for scale-up and nanoparticle purification were explored, providing access to centimeter-scale pressed pellets of polyol-synthesized nanopowders and a bacteriophage-mediated method for separating impure nanoparticle mixtures into their components. Several advances were made in the synthesis of iron selenide and related superconducting materials, including the production of colloidal Fe

  7. 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.

  8. Magnetic Assisted Colloidal Pattern Formation

    Science.gov (United States)

    Yang, Ye

    phase transitions in condensed matter systems that can be tracked with single particle resolution. Compared with other research on colloidal crystal formation, my research has focused on multi-component colloidal systems of magnetic and non-magnetic colloids immersed in a ferrofluid. Initially, I studied the types of patterns that form as a function of the concentrations of the different particles and ferrofluid, and I discovered a wide variety of chains, rings and crystals forming in bi-component and tri-component systems. Based on these results, I narrowed my focus to one specific crystal structure (checkerboard lattice) as a model of phase transformations in alloy. Liquid/solid phase transitions were studied by slowly adjusting the magnetic field strength, which serves to control particle-particle interactions in a manner similar to controlling the physical temperature of the fluid. These studies were used to determine the optimal conditions for forming large single crystal structures, and paved the way for my later work on solid/solid phase transitions when the angle of the external field was shifted away from the normal direction. The magnetostriction coefficient of these crystals was measured in low tilt angle of the applied field. At high tilt angles, I observed a variety of martensitic transformations, which followed different pathways depending on the crystal direction relative to the in-plane field. In the last part of my doctoral studies, I investigated colloidal patterns formed in a superimposed acoustic and magnetic field. In this approach, the magnetic field mimics "temperature", while the acoustic field mimics "pressure". The ability to simultaneously tune both temperature and pressure allows for more efficient exploration of phase space. With this technique I demonstrated a large class of particle structures ranging from discrete molecule-like clusters to well ordered crystal phases. Additionally, I demonstrated a crosslinking strategy based on

  9. One more chiral drug prone to spontaneous resolution: Binary phase diagram, absolute configuration, and crystal packing of bevantolol hydrochloride

    Science.gov (United States)

    Bredikhina, Zemfira A.; Zakharychev, Dmitry V.; Gubaidullin, Aidar T.; Bredikhin, Alexander A.

    2009-11-01

    Spontaneous resolution of cardioselective β1-adrenergic blocker bevantolol hydrochloride1·HCl was established by IR spectroscopy, differential scanning calorimetry, and by single crystal X-ray analysis both for enantiopure and racemic samples. The absolute configuration of 1·HCl was evaluated through Flack parameter method. The molecular structure and crystal packing details were evaluated; the symmetry independent fragment of the P1 unit cell consists of two molecules which have almost identical spatial arrangement, but differ sufficiently in the nature of nitrogen atoms: quaternary form in one case and free amine form in the other.

  10. Design of nanoengineered hybrid PVA/PNIPAm/CaCl2/SiO2-Polystyrene (PSt) colloidal crystal hydrogel coatings that sweat/rehydrate H2O from the atmosphere to give sustainable cooling and self-indicate their state

    Science.gov (United States)

    Eloi, Jean-Charles; Worsley, Myles P.; Sermon, Paul A.; Healy, William; Dimech, Christine

    2016-09-01

    The potential for nanoengineering hybrid PVA hydrogel and hydrogel microsphere optical coatings is demonstrated with fine-tuning by the addition of (i) PNIPAm domains, (ii) water-hunting humectant CaCl2, and (ii) polystyrene or SiO2 colloidal crystals. The design and application onto substrates of the hydrogel scaffold is described. The addition of a temperature-triggered component as well as humectant and NIR reflectors are reported. The hybrid hydrogels appeared effective in sustainable adsorption cooling technology (ACT) over sustained periods. It is shown that the thermoresponsive (PNIPAm) domains act as an extra reserve, sweating water above 305K, prolonging the controlled release of water. It is also reported that the addition of humectant is crucial for the natural re-hydration of the hydrogels. For the moment PNIPAm microspheres have only short- lived ACT properties. Finally, coating with microspheres (MSs) in hydrogels produces a visible-NIR reflector effect that may allow optical feedback on ACT.

  11. Shape recognition of microbial cells by colloidal cell imprints

    Science.gov (United States)

    Borovička, Josef; Stoyanov, Simeon D.; Paunov, Vesselin N.

    2013-08-01

    We have engineered a class of colloids which can recognize the shape and size of targeted microbial cells and selectively bind to their surfaces. These imprinted colloid particles, which we called ``colloid antibodies'', were fabricated by partial fragmentation of silica shells obtained by templating the targeted microbial cells. We successfully demonstrated the shape and size recognition between such colloidal imprints and matching microbial cells. High percentage of binding events of colloidal imprints with the size matching target particles was achieved. We demonstrated selective binding of colloidal imprints to target microbial cells in a binary mixture of cells of different shapes and sizes, which also resulted in high binding selectivity. We explored the role of the electrostatic interactions between the target cells and their colloid imprints by pre-coating both of them with polyelectrolytes. Selective binding occurred predominantly in the case of opposite surface charges of the colloid cell imprint and the targeted cells. The mechanism of the recognition is based on the amplification of the surface adhesion in the case of shape and size match due to the increased contact area between the target cell and the colloidal imprint. We also tested the selective binding for colloid imprints of particles of fixed shape and varying sizes. The concept of cell recognition by colloid imprints could be used for development of colloid antibodies for shape-selective binding of microbes. Such colloid antibodies could be additionally functionalized with surface groups to enhance their binding efficiency to cells of specific shape and deliver a drug payload directly to their surface or allow them to be manipulated using external fields. They could benefit the pharmaceutical industry in developing selective antimicrobial therapies and formulations.

  12. Colloidal Plasmonic Titanium Nitride Nanoparticles: Properties and Applications

    DEFF Research Database (Denmark)

    Guler, Urcan; Suslov, Sergey; Kildishev, Alexander V.;

    2015-01-01

    Optical properties of colloidal plasmonic titanium nitride nanoparticles are examined with an eye on their photothermal and photocatalytic applications via transmission electron microscopy and optical transmittance measurements. Single crystal titanium nitride cubic nanoparticles with an average...

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Phase behaviour of colloids suspended in a near-critical solvent : A mean-field approach

    NARCIS (Netherlands)

    Edison, John R.; Belli, Simone; Evans, Robert; Van Roij, René; Dijkstra, Marjolein

    2015-01-01

    Colloids suspended in a binary solvent may, under suitable thermodynamic conditions, experience a wide variety of solvent-mediated interactions that can lead to colloidal phase transitions and aggregation phenomena. We present a simple mean-field theory, based on free-volume arguments, that describe

  18. 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.

  19. 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.

  20. Inventions Utilizing Microfluidics and Colloidal Particles

    Science.gov (United States)

    Marr, David W.; Gong, Tieying; Oakey, John; Terray, Alexander V.; Wu, David T.

    2009-01-01

    Several related inventions pertain to families of devices that utilize microfluidics and/or colloidal particles to obtain useful physical effects. The families of devices can be summarized as follows: (1) Microfluidic pumps and/or valves wherein colloidal-size particles driven by electrical, magnetic, or optical fields serve as the principal moving parts that propel and/or direct the affected flows. (2) Devices that are similar to the aforementioned pumps and/or valves except that they are used to manipulate light instead of fluids. The colloidal particles in these devices are substantially constrained to move in a plane and are driven to spatially order them into arrays that function, variously, as waveguides, filters, or switches for optical signals. (3) Devices wherein the ultra-laminar nature of microfluidic flows is exploited to effect separation, sorting, or filtering of colloidal particles or biological cells in suspension. (4) Devices wherein a combination of confinement and applied electrical and/or optical fields forces the colloidal particles to become arranged into three-dimensional crystal lattices. Control of the colloidal crystalline structures could be exploited to control diffraction of light. (5) Microfluidic devices, incorporating fluid waveguides, wherein switching of flows among different paths would be accompanied by switching of optical signals.

  1. Shaping Crystals using Electrophoresis

    Science.gov (United States)

    Palacci, Jeremie; Mackiewicz, Kristian

    2016-11-01

    Electrophoresis is size and shape independent as stressed by Morrison in his seminal paper. Here we present an original approach to reshape colloidal crystals using an electric field as a carving tool.

  2. 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...

  3. 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.

  4. 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.

  5. Fabrication and applications of functional polymer colloidal photonic crystals%功能型聚合物光子晶体的制备及应用

    Institute of Scientific and Technical Information of China (English)

    黄羽; 王京霞; 宋延林; 江雷

    2012-01-01

    Photonic crystals have attracted wide attentions due to their special light manipulation properties and promising applications in various high-performance optic devices. In this paper, we present series of fabrication of functional polymer photonic crystals based on well-designed latex particles and demonstrate their extensive applications in visible monitor, ultrasensive detection, high-efficient catalyst, and high-performance light storage.%光子晶体因其特殊的光调控性能,在各类高性能光学器件方面具有重要的应用前景.本文主要阐述了功能型聚合物光子晶体的制备方法及其在防护涂层、高效发光、高灵敏检测和高性能光信息存储等方面的应用.

  6. 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.

  7. Preparation of colloid photonic crystal structural color glaze%胶体光子晶体结构色釉的制备

    Institute of Scientific and Technical Information of China (English)

    王芬; 安凯妮; 朱建锋; 董龙龙; 盖言成; 李伟东; 李强

    2014-01-01

    Structural color glazes were assembled by a variety of different size of monodisperse silica colloidal microspheres prepared by sol-gel on porcelain body with vertical deposition method .T he influences of particle size on structural color and the control methods of particle size were researched .SEM analysis shows that the size of the silica microspheres become large as increasing amount of ammonia and TEOS in the preparation process ,but will decrea-ses as the increase of reaction temperature .The size of the microspheres will increase to the maximum and then decrease with the rise of water concentration .And it is found that the films with good three-dimensional orderly close packing structure could have red-shift of the color by increasing the particle size ,by this way ,we have made various structural colors g laze .%采用溶胶凝胶法制备了多种不同粒径的单分散二氧化硅胶体微球,并利用制备的微球以垂直沉积自组装法在瓷胎表面制备了颜色艳丽的结构色釉.研究了微球粒径的工艺控制方法及微球尺寸对结构色的影响.SEM 分析表明:在二氧化硅微球制备过程中,随着反应液中氨水和正硅酸乙酯浓度的增大,微球粒径逐渐增大;水解、缩聚反应温度升高,微球尺寸会逐渐减小;体系水浓度增大,二氧化硅微球尺寸先增大后减小,存在一个峰值.薄膜分析表明,具有良好三维有序密堆积结构的薄膜,其颜色随着自组装用微球粒径的增大发生红移,色调发生变化,从而能够生成多种结构色釉.

  8. Optical Manipulation and Application by Three Dimensional Colloidal Photonic Crystals%三维胶体光子晶体对光的调控与应用研究

    Institute of Scientific and Technical Information of China (English)

    李珩; 王京霞; 王荣明; 宋延林

    2011-01-01

    21世纪在光子技术领域中操控光子已成为核心的研究内容.胶体光子晶体因其特殊的周期结构而具有光子禁带的特性,从而可以对特定频率的光进行调控,其应用涵盖了光、电、催化、传感、显示、检测等众多领域,为光功能材料的结构设计和性能优化提供了参考依据.本文主要从两个方面阐述近年来胶体光子晶体对光的调控作用与应用,一方面,光子晶体的光子禁带受外界环境刺激下的调控,其核心是在光子晶体中填充响应性的材料,从而引起光子晶体晶格常数或折光指数的变化,这在化学及生物传感器技术领域有着广阔的应用前景;另一方面,光子晶体对嵌入在其中的发射物质的光学行为能实现有效的控制,这将有力地推动光学器件的发展.文章最后还对胶体光子晶体今后的发展进行了展望.%Manipulation of photons has become the core studies in area of photonics in the 21th century.Colloidal photonic crystals ( CPC), with the characteristic of photonic stopband due to their periodic structures, can control the propagation of light in a certain direction, which show applications in optics, electronics, catalysis, display, detection and so on.Furthermore, CPC can offer the guidance for designing structures and optimizing properties of optical functional materials.In this paper, the recent achievements on applications in this field are presented from two aspects.On the one hand, the optical manipulation of photonic crystals is based on changing the stopband characteristics through variation of the refractive index or the lattice constant by applying external stimuli, which provides a promising strategy to develop the technology in chemical sensors and biosensors.On the other hand, the optical behavior can be effectively controlled based on emitters embedded in PCs, which promotes the development of optical devices.Finally, this paper brings forward perspectives toward

  9. Interacting binaries

    CERN Document Server

    Shore, S N; van den Heuvel, EPJ

    1994-01-01

    This volume contains lecture notes presented at the 22nd Advanced Course of the Swiss Society for Astrophysics and Astronomy. The contributors deal with symbiotic stars, cataclysmic variables, massive binaries and X-ray binaries, in an attempt to provide a better understanding of stellar evolution.

  10. 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

  11. 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

  12. 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

  13. Simultaneous synthesis/assembly of anisotropic cake-shaped porphyrin particles toward colloidal microcrystals.

    Science.gov (United States)

    Wang, Ting; Kuang, Minxuan; Jin, Feng; Cai, Jinhua; Shi, Lei; Zheng, Yongmei; Wang, Jingxia; Jiang, Lei

    2016-03-01

    The one-step synthesis/assembly of a cake-shaped porphyrin colloidal microcrystal with tailored height-diameter was demonstrated based on interfacial assembly and the water-droplet template. The as-fabricated anisotropic colloidal crystals showed special optic properties and enhanced optic-limiting behavior.

  14. 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

  15. Assembly of Colloidal Materials Using Bioadhesive Interactions

    Science.gov (United States)

    Hammer, Daniel A.; Hiddessen, Amy L.; Tohver, Valeria; Crocker, John C.; Weitz, David A.

    2002-01-01

    We have pursued the use of biological crosslinking molecules of several types to make colloidal materials at relatively low volume fraction of colloidal particles. The objective is to make binary alloys of colloidal particles, made of two different colloidal particles coated with complementary biological lock-and-key binding molecules, which assemble due to the biological specificity. The long-term goal is to use low affinity lock-and-key biological interactions, so that the can anneal to form crystalline states. We have used a variety of different surface chemistries in order to make colloidal materials. Our first system involved using selectin-carbohydrate (sialyl-Lewis) interactions; this chemistry is derived from immune system. This chemical interaction is of relatively low affinity, with timescales for dissociation of several seconds. Furthermore, the adhesion mediated by these molecules can be reversed by the chelation of calcium atoms; thus assembled structures can be disassembled reversibly. Our second system employed avidin-biotin chemistry. This well-studied system is of high affinity, and is generally irreversible on a laboratory time-scale. Thus, we would expect selectin-carbohydrate interactions at high molecular density and avidin-biotin interactions to give kinetically-trapped structures; however, at low densities, we would expect significant differences in the structure and dynamics of the two materials, owing to their very different release rates. We have also begun to use a third chemistry - DNA hybridization. By attaching single stranded DNA oligonucleotide chains to beads, we can drive the assembly of colloidal materials by hybridization of complementary DNA chains. It is well known that DNA adenosine-thymine (A-T) and guanine-cytosine (G-C) bases hybridize pairwise with a Gibbs free energy change of 1.7 kcal/mol per base; thus, the energy of the assembly can be modulated by altering the number of complementary bases in the DNA chains. Using

  16. Alternating strings and clusters in suspensions of charged colloids

    CERN Document Server

    Everts, Jeffrey C; van Blaaderen, Alfons; van Roij, René

    2016-01-01

    We report the formation of alternating strings and clusters in a binary suspension of repulsive charged colloids with double layers larger than the particle size. Within a binary cell model we include many-body and charge-regulation effects under the assumption of a constant surface po- tential, and consider their repercussions on the two-particle interaction potential. We find that the formation of induced dipoles close to a charge-reversed state may explain the formation of these structures. Finally, we will touch upon the formation of dumbbells and small clusters in a one-component system, where the effective electrostatic interaction is always repulsive.

  17. Efficient neighbor list calculation for molecular simulation of colloidal systems using graphics processing units

    Science.gov (United States)

    Howard, Michael P.; Anderson, Joshua A.; Nikoubashman, Arash; Glotzer, Sharon C.; Panagiotopoulos, Athanassios Z.

    2016-06-01

    We present an algorithm based on linear bounding volume hierarchies (LBVHs) for computing neighbor (Verlet) lists using graphics processing units (GPUs) for colloidal systems characterized by large size disparities. We compare this to a GPU implementation of the current state-of-the-art CPU algorithm based on stenciled cell lists. We report benchmarks for both neighbor list algorithms in a Lennard-Jones binary mixture with synthetic interaction range disparity and a realistic colloid solution. LBVHs outperformed the stenciled cell lists for systems with moderate or large size disparity and dilute or semidilute fractions of large particles, conditions typical of colloidal systems.

  18. A facile synthesis of Te nanoparticles with binary size distribution by green chemistry.

    Science.gov (United States)

    He, Weidong; Krejci, Alex; Lin, Junhao; Osmulski, Max E; Dickerson, James H

    2011-04-01

    Our work reports a facile route to colloidal Te nanocrystals with binary uniform size distributions at room temperature. The binary-sized Te nanocrystals were well separated into two size regimes and assembled into films by electrophoretic deposition. The research provides a new platform for nanomaterials to be efficiently synthesized and manipulated.

  19. 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

  20. 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.

  1. 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.

  2. Diffusion of colloidal fluids in random porous media.

    Science.gov (United States)

    Chávez-Rojo, M A; Juárez-Maldonado, R; Medina-Noyola, M

    2008-04-01

    The diffusive relaxation of a colloidal fluid adsorbed in a porous medium depends on many factors, including the concentration and composition of the adsorbed colloidal fluid, the average structure of the porous matrix, and the nature of the colloid-colloid and colloid-substrate interactions. A simple manner to describe these effects is to model the porous medium as a set of spherical particles fixed in space at random positions with prescribed statistical structural properties. Within this model one may describe the relaxation of concentration fluctuations of the adsorbed fluid by simply setting to zero the short-time mobility of one species (the porous matrix) in a theory of the dynamics of equilibrium colloidal mixtures, or by extending such dynamic theory to explicitly consider the porous matrix as a random external field, as recently done in the framework of mode coupling theory [V. Krakoviack, Phys. Rev. Lett. 94, 065703 (2005)]. Here we consider the first approach and employ the self-consistent generalized Langevin equation (SCGLE) theory of the dynamics of equilibrium colloidal mixtures, to describe the dynamics of the mobile component. We focus on the short- and intermediate-time regimes, which we compare with Brownian dynamics simulations involving a binary mixture with screened Coulomb interactions for two models of the average static structure of the matrix: a porous matrix constructed by quenching configurations of an equilibrium mixture in which both species were first equilibrated together, and a preexisting matrix with prescribed average structure, in which we later add the mobile species. We conclude that in both cases, if the correct static structure factors are provided as input, the SCGLE theory correctly predicts the main features of the dynamics of the permeating fluid.

  3. 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.

  4. Colloidal gold and silica in mesothermal vein systems

    Science.gov (United States)

    Herrington, R. J.; Wilkinson, J. J.

    1993-06-01

    Some of the textural features of mesothermal gold-quartz veins may be best explained by the initial precipitation of amorphous silica gel (colloid), which subsequently crystallizes to quartz. This can occur in brittle-ductile shear zones where a significant fluid-pressure drop occurs during stick-slip failure. Such a process rapidly supersaturates the hydrothermal fluid with respect to amorphous silica, which precipitates instead of quartz, owing to favorable kinetics. Depressurization also commonly leads to fluid unmixing and destabilization of soluble gold complexes. However, the presence of colloidal silica can stabilize gold colloid, allowing further transport of particulate gold in suspension in the hydrothermal fluid. Silica gel would be highly unstable under mesothermal conditions and would undergo rapid syneresis and crystallization to form quartz; solid impurities would tend to be expelled toward grain boundaries. This model can account for the primary anhedral aggregate textures typical of mesothermal quartz veins, the concentration of gold along grain boundaries and the formation of discrete gold nuggets, and the rare occurrence of low-order silica polymorphs and relict spheroidal structures. The transport of gold in colloidal form may be one reason for the frequently consistent bulk grade distribution in gold-quartz vein systems over many hundreds of metres (in some cases kilometres) of depth. In addition, the formation of charged colloidal particles may help to explain the attraction of gold grains to specific mineral surfaces.

  5. 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

  6. Peculiarities of hopping conduction in p-Hg sub 0 sub . sub 7 sub 8 Cd sub 0 sub . sub 2 sub 2 Te crystals at binary doping

    CERN Document Server

    Bogoboyashchij, V V

    2002-01-01

    Electric conductivity and the Hall effect within the 4.2-125 K temperature range have been investigated in p-Hg sub 0 sub . sub 7 sub 8 Cd sub 0 sub . sub 2 sub 2 Te crystals, containing 3 x 10 sup 1 sup 6 cm sup - sup 3 of copper impurities and 1.83 x 10 sup 1 sup 6 cm sup - sup 3 of mercury vacancies (together or separately). The epsilon sub 1 -conductivity due to free holes above 10-12 K and the hopping conductivity below 8-10 K are dominant in such crystals respectively. It was found that the epsilon sub 1 -conductivity in copper-doped crystals is independent of the vacancy presence, while the hopping conductivity essentially increases due to the vacancy availability. This phenomenon is explained in terms hole joining neutral mercury vacancies.The binding energy is calculated; it equal 3.7 meV in background state

  7. 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.

  8. 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.

  9. 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

  10. Three-dimensional positioning and control of colloidal objects utilizing engineered liquid crystalline defect networks.

    Science.gov (United States)

    Yoshida, H; Asakura, K; Fukuda, J; Ozaki, M

    2015-05-21

    Topological defects in liquid crystals not only affect the optical and rheological properties of the host, but can also act as scaffolds in which to trap nano or micro-sized colloidal objects. The creation of complex defect shapes, however, often involves confining the liquid crystals in curved geometries or adds complex-shaped colloidal objects, which are unsuitable for device applications. Using topologically patterned substrates, here we demonstrate the controlled generation of three-dimensional defect lines with non-trivial shapes and even chirality, in a flat slab of nematic liquid crystal. By using the defect lines as templates and the electric response of the liquid crystals, colloidal superstructures are constructed, which can be reversibly reconfigured at a voltage as low as 1.3 V. Three-dimensional engineering of the defect shapes in liquid crystals is potentially useful in the fabrication of self-healing composites and in stabilizing artificial frustrated phases.

  11. 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.

  12. 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

  13. Influence of non-covalent modification of multiwalled carbon nanotubes on the crystallization behaviour of binary blends of polypropylene and polyamide 6.

    Science.gov (United States)

    Mukhopadhyay, Nabaneeta; Panwar, Ajay S; Kumar, Gulshan; Samajdar, I; Bhattacharyya, Arup R

    2015-02-14

    Blends of polypropylene (PP) and polyamide 6 (PA6) with multiwalled carbon nanotubes (MWNTs) were prepared using different processing strategies in a twin-screw micro-compounder. The effect of MWNTs on the crystallization behaviour of the PP phase and the PA6 phase of the blend has been investigated through non-isothermal crystallization studies by differential scanning calorimetric analysis. Furthermore, the effect of the addition of the compatibilizer (PP-g-MA) and the modification of MWNTs (m-MWNTs) with a non-covalent organic modifier (Li-salt of 6 amino hexanoic acid, Li-AHA) has also been studied in context to the crystallization behaviour of the PP and PA6 phase in the blend. The crystallization studies have indicated a significant increase in bulk crystallization temperature of the PP phase in the blend in the presence of MWNTs. Moreover, the formation of 'trans-lamellar crystalline' structure consisting of PA6 'trans-crystalline lamellae' on MWNTs surface was facilitated in the case of blends prepared via 'protocol 2' as compared to the corresponding blends prepared via 'protocol 1'. Wide angle X-ray diffraction analysis has showed the existence of a β-polymorph of the PP phase due to incorporation of the PA6 phase in the blend. Addition of MWNTs in the blends has facilitated further β-crystalline structure formation of the PP phase. In the presence of m-MWNTs, a higher β-fraction was observed in the PP phase as compared to the blend with pristine MWNTs. Addition of PP-g-MA has suppressed the β-phase formation in the PP phase in the blend. X-ray bulk texture analysis revealed that incorporation of PA6 as well as pristine/modified MWNTs has influenced the extent of orientation of the PP chains towards specific crystalline planes in various blend compositions of PP and PA6.

  14. Colloidal nanocrystal synthesis and the organic-inorganicinterface

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Yadong; Alivisatos, A. Paul

    2005-05-12

    Colloidal nanocrystals are nanometer-sized, solution-grown inorganic particles stabilized by a layer of surfactants attached to their surface. The inorganic cores exhibit useful properties controlled by composition as well as size and shape, while the surfactant coating ensures that these structures are easy to fabricate and process. It is this combination of features that makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. But their full potential can only be exploited if we achieve exquisite control over their composition, size, shape, crystal structure and surface properties. Here we review what is known about nanocrystal growth and outline strategies for controlling it.

  15. 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.

  16. Computational crystallization.

    Science.gov (United States)

    Altan, Irem; Charbonneau, Patrick; Snell, Edward H

    2016-07-15

    Crystallization is a key step in macromolecular structure determination by crystallography. While a robust theoretical treatment of the process is available, due to the complexity of the system, the experimental process is still largely one of trial and error. In this article, efforts in the field are discussed together with a theoretical underpinning using a solubility phase diagram. Prior knowledge has been used to develop tools that computationally predict the crystallization outcome and define mutational approaches that enhance the likelihood of crystallization. For the most part these tools are based on binary outcomes (crystal or no crystal), and the full information contained in an assembly of crystallization screening experiments is lost. The potential of this additional information is illustrated by examples where new biological knowledge can be obtained and where a target can be sub-categorized to predict which class of reagents provides the crystallization driving force. Computational analysis of crystallization requires complete and correctly formatted data. While massive crystallization screening efforts are under way, the data available from many of these studies are sparse. The potential for this data and the steps needed to realize this potential are discussed.

  17. FABRICATION OF PHOTONIC CRYSTAL WITH SUPERLATTICES

    Institute of Scientific and Technical Information of China (English)

    SUN Cheng; Chen Haihua; Zhang Jizhong; Wei Hongmei; Gu Zhongze

    2006-01-01

    A novel technique was used to fabricate three-dimensional photonic crystals with superlattices. The super structure was fabricated by assembling monodispersed microspheres in the grooves of the scales of morpho butterfly, which makes the photonic crystal being composed of two kinds of different photonic structures (natural groove structure of butterfly wing and artificial microspherical colloids arrangement). The superstructural photonic crystal exhibits some unique optical properties different from both the butterfly wing and the colloidal crystal. The approach exhibited here provides a new way for fabricate photonic crystals with superlattices.

  18. The structures of binary compounds

    CERN Document Server

    Hafner, J; Jensen, WB; Majewski, JA; Mathis, K; Villars, P; Vogl, P; de Boer, FR

    1990-01-01

    - Up-to-date compilation of the experimental data on the structures of binary compounds by Villars and colleagues. - Coloured structure maps which order the compounds into their respective structural domains and present for the first time the local co-ordination polyhedra for the 150 most frequently occurring structure types, pedagogically very helpful and useful in the search for new materials with a required crystal structure. - Crystal co-ordination formulas: a flexible notation for the interpretation of solid-state structures by chemist Bill Jensen. - Recent important advances in unders

  19. Large-scale assembly of colloidal particles

    Science.gov (United States)

    Yang, Hongta

    This study reports a simple, roll-to-roll compatible coating technology for producing three-dimensional highly ordered colloidal crystal-polymer composites, colloidal crystals, and macroporous polymer membranes. A vertically beveled doctor blade is utilized to shear align silica microsphere-monomer suspensions to form large-area composites in a single step. The polymer matrix and the silica microspheres can be selectively removed to create colloidal crystals and self-standing macroporous polymer membranes. The thickness of the shear-aligned crystal is correlated with the viscosity of the colloidal suspension and the coating speed, and the correlations can be qualitatively explained by adapting the mechanisms developed for conventional doctor blade coating. Five important research topics related to the application of large-scale three-dimensional highly ordered macroporous films by doctor blade coating are covered in this study. The first topic describes the invention in large area and low cost color reflective displays. This invention is inspired by the heat pipe technology. The self-standing macroporous polymer films exhibit brilliant colors which originate from the Bragg diffractive of visible light form the three-dimensional highly ordered air cavities. The colors can be easily changed by tuning the size of the air cavities to cover the whole visible spectrum. When the air cavities are filled with a solvent which has the same refractive index as that of the polymer, the macroporous polymer films become completely transparent due to the index matching. When the solvent trapped in the cavities is evaporated by in-situ heating, the sample color changes back to brilliant color. This process is highly reversible and reproducible for thousands of cycles. The second topic reports the achievement of rapid and reversible vapor detection by using 3-D macroporous photonic crystals. Capillary condensation of a condensable vapor in the interconnected macropores leads to the

  20. 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.

  1. Binary effectivity rules

    DEFF Research Database (Denmark)

    Keiding, Hans; Peleg, Bezalel

    2006-01-01

    is binary if it is rationalized by an acyclic binary relation. The foregoing result motivates our definition of a binary effectivity rule as the effectivity rule of some binary SCR. A binary SCR is regular if it satisfies unanimity, monotonicity, and independence of infeasible alternatives. A binary...... effectivity rule is regular if it is the effectivity rule of some regular binary SCR. We characterize completely the family of regular binary effectivity rules. Quite surprisingly, intrinsically defined von Neumann-Morgenstern solutions play an important role in this characterization...

  2. Ordered two-dimensional superstructures of colloidal octapod-shaped nanocrystals on flat substrates

    NARCIS (Netherlands)

    Qi, W.; Graaf, J. de; Qiao, F.; Marras, S.; Manna, L.; Dijkstra, M.

    2012-01-01

    We studied crystal structures in a monolayer consisting of anisotropic branched colloidal (nano)octapods. Experimentally, octapods were observed to form a monolayer on a substrate with a square-lattice crystal structure by drop-casting and fast evaporation of solvent. The experimental results were a

  3. Interface Characteristics Between Colloidal Gold and Kaolinite Surface by XPS

    Institute of Scientific and Technical Information of China (English)

    HONG Hanlie; TIE Liyun; BIAN Qiujuan; ZHOU Yong

    2006-01-01

    The distribution of gold colloids in kaolinite and the interaction between gold and kaolinite surface were investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). There is strong interaction between the gold particles and the edge surfaces of kaolinite,in low pH solution,the edge surface of kaolinite is positively charged and electrostatic attractive force between colloide gold particles and the positive edge surface of kaolinite would facilitate the adsorption of colloidal gold particles onto the suface. TEM observation shows that the aggregate morphology of gold particles was dominated by particle-particle interaction and gold particles were adsorbed on the edge surface of kaolinite crystals, resulting from the electrostatic attractive force between colloidal gold particles and the positive surfaces of kaolinite. XPS data show that in Au4f electron spectra there are four energy peaks related to gold, 83.8 eV, 85.7 eV, 87.5 eV, and 89.4 eV, respectively, which suggests that in chemical states there are metallic gold and Au bonded to O, similar to the form of Au2O3, and composite Au2O3 is formed between the edge surface of kaolinite and colloidal gold surface.

  4. Colloidal membranes of hard rods: unified theory of free edge structure and twist walls.

    Science.gov (United States)

    Kaplan, C Nadir; Meyer, Robert B

    2014-07-14

    Monodisperse suspensions of rod like chiral fd viruses are condensed into a rod-length thick colloidal monolayers of aligned rods by depletion forces. Twist deformations of the molecules are expelled to the monolayer edge as in a chiral smectic A liquid crystal, and a cholesteric band forms at the edge. Coalescence of two such isolated membranes results in a twist wall sandwiched between two regions of aligned rods, dubbed π-walls. By modeling the membrane as a binary fluid of coexisting cholesteric and chiral smectic A liquid-crystalline regions, we develop a unified theory of the π-walls and the monolayer edge. The mean-field analysis of our model yields the molecular tilt profiles, the local thickness change, and the crossover from smectic to cholesteric behavior at the monolayer edge and across the π-wall. Furthermore, we calculate the line tension associated with the formation of these interfaces. Our model offers insights regarding the stability and the detailed structure of the π-wall and the monolayer edge.

  5. Information storage and retrieval in a single levitating colloidal particle

    Science.gov (United States)

    Myers, Christopher J.; Celebrano, Michele; Krishnan, Madhavi

    2015-10-01

    The binary switch is a basic component of digital information. From phase-change alloys to nanomechanical beams, molecules and atoms, new strategies for controlled bistability hold great interest for emerging technologies. We present a generic methodology for precise and parallel spatiotemporal control of nanometre-scale matter in a fluid, and demonstrate the ability to attain digital functionalities such as switching, gating and data storage in a single colloid, with further implications for signal amplification and logic operations. This fluid-phase bit can be arrayed at high densities, manipulated by either electrical or optical fields, supports low-energy, high-speed operation and marks a first step toward ‘colloidal information’. The principle generalizes to any system where spatial perturbation of a particle elicits a differential response amenable to readout.

  6. Development of photonic crystal structures for on-board optical communication

    NARCIS (Netherlands)

    Khan, M.U.; Justice, J.; Boersma, A.; Mourad, M.; Ee, R.J. van; Blaaderen, A. van; Wijnhoven, J.; Corbett, B.

    2014-01-01

    We present designs for sharp bends in polymer waveguides using colloidal photonic crystal (PhC) structures. Both silica (SiO2) sphere based colloidal PhC and core-shell colloidal PhC structures having a titania (TiO 2) core inside silica (SiO2) shells are simulated. The simulation results show that

  7. 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.

  8. DHS Internship Summary-Crystal Assembly at Different Length Scales

    Energy Technology Data Exchange (ETDEWEB)

    Mishchenko, L

    2009-08-06

    I was part of a project in which in situ atomic force microscopy (AFM) was used to monitor growth and dissolution of atomic and colloidal crystals. At both length scales, the chemical environment of the system greatly altered crystal growth and dissolution. Calcium phosphate was used as a model system for atomic crystals. A dissolution-reprecipitation reaction was observed in this first system, involving the conversion of brushite (DCPD) to octacalcium phosphate (OCP). In the second system, polymeric colloidal crystals were dissolved in an ionic solvent, revealing the underlying structure of the crystal. The dissolved crystal was then regrown through an evaporative step method. Recently, we have also found that colloids can be reversibly deposited in situ onto an ITO (indium tin oxide) substrate via an electrochemistry setup. The overall goal of this project was to develop an understanding of the mechanisms that control crystallization and order, so that these might be controlled during material synthesis. Controlled assembly of materials over a range of length scales from molecules to nanoparticles to colloids is critical for designing new materials. In particular, developing materials for sensor applications with tailorable properties and long range order is important. In this work, we examine two of these length scales: small molecule crystallization of calcium phosphate (whose crystal phases include DCPD, OCP, and HAP) and colloidal crystallization of Poly(methyl methacrylate) beads. Atomic Force Microscopy is ideal for this line of work because it allows for the possibility of observing non-conducting samples in fluid during growth with high resolution ({approx} 10 nm). In fact, during atomic crystal growth one can observe changes in atomic steps, and with colloidal crystals, one can monitor the individual building blocks of the crystal. Colloids and atoms crystallize under the influence of different forces acting at different length scales as seen in Table 1

  9. Critical Casimir interactions around the consolute point of a binary solvent.

    Science.gov (United States)

    Mohry, T F; Kondrat, S; Maciołek, A; Dietrich, S

    2014-08-14

    Spatial confinement of a near-critical medium changes its fluctuation spectrum and modifies the corresponding order parameter distribution, resulting in effective, so-called critical Casimir forces (CCFs) acting on the confining surfaces. These forces are attractive for like boundary conditions of the order parameter at the opposing surfaces of the confinement. For colloidal particles dissolved in a binary liquid mixture acting as a solvent close to its critical point of demixing, one thus expects the emergence of phase segregation into equilibrium colloidal liquid and gas phases. We analyze how such phenomena occur asymmetrically in the whole thermodynamic neighborhood of the consolute point of the binary solvent. By applying field-theoretical methods within mean-field approximation and the semi-empirical de Gennes-Fisher functional, we study the CCFs acting between planar parallel walls as well as between two spherical colloids and their dependence on temperature and on the composition of the near-critical binary mixture. We find that for compositions slightly poor in the molecules preferentially adsorbed at the surfaces, the CCFs are significantly stronger than at the critical composition, thus leading to pronounced colloidal segregation. The segregation phase diagram of the colloid solution following from the calculated effective pair potential between the colloids agrees surprisingly well with experiments and simulations.

  10. 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.

  11. Colloidal Plasmonic Titanium Nitride Nanoparticles: Properties and Applications

    CERN Document Server

    Guler, Urcan; Kildishev, Alexander V; Boltasseva, Alexandra; Shalaev, Vladimir M

    2014-01-01

    Optical properties of colloidal plasmonic titanium nitride nanoparticles are examined with an eye on their photothermal via transmission electron microscopy and optical transmittance measurements. Single crystal titanium nitride cubic nanoparticles with an average size of 50 nm exhibit plasmon resonance in the biological transparency window. With dimensions optimized for efficient cellular uptake, the nanoparticles demonstrate a high photothermal conversion efficiency. A self-passivating native oxide at the surface of the nanoparticles provides an additional degree of freedom for surface functionalization.

  12. Synthesis of zirconia colloidal dispersions by forced hydrolysis

    Directory of Open Access Journals (Sweden)

    JELENA P. MARKOVIC

    2006-06-01

    Full Text Available Different zirconia colloidal dispersions (sols were prepared from zirconyl oxynitrate and zirconyl oxychloride solutions by forced hydrolysis. Vigorously stirred acidic solutions of these salts were refluxed at 102 oC for 24 h. Characterization of the obtained sols (pH, solid phase content, crystal structure was performed by potentiometric, XRD, TGA/DTA and SEM measurements. The prepared sols contained almost spherical monoclinic hydrated zirconia particles 7–10 nm in diameter.

  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. The Crystal Structure of a Binary Complex of Two Pseudopilins: EpsI And EpsJ From the Type 2 Secretion System of Vibrio Vulnificus

    Energy Technology Data Exchange (ETDEWEB)

    Yanez, M.E.; Korotkov, K.V.; Abendroth, J.; Hol, W.G.J.

    2009-05-28

    Type II secretion systems (T2SS) translocate virulence factors from the periplasmic space of many pathogenic bacteria into the extracellular environment. The T2SS of Vibrio cholerae and related species is called the extracellular protein secretion (Eps) system that consists of a core of multiple copies of 11 different proteins. The pseudopilins, EpsG, EpsH, EpsI, EpsJ and EpsK, are five T2SS proteins that are thought to assemble into a pseudopilus, which is assumed to interact with the outer membrane pore, and may actively participate in the export of proteins. We report here biochemical evidence that the minor pseudopilins EpsI and EpsJ from Vibrio species interact directly with one another. Moreover, the 2.3 {angstrom} resolution crystal structure of a complex of EspI and EpsJ from Vibrio vulnificus represents the first atomic resolution structure of a complex of two different pseudopilin components from the T2SS. Both EpsI and EpsJ appear to be structural extremes within the family of type 4a pilin structures solved to date, with EpsI having the smallest, and EpsJ the largest, 'variable pilin segment' seen thus far. A high degree of sequence conservation in the EpsI:EpsJ interface indicates that this heterodimer occurs in the T2SS of a large number of bacteria. The arrangement of EpsI and EpsJ in the heterodimer would correspond to a right-handed helical character of proteins assembled into a pseudopilus.

  16. 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...

  17. 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.

  18. 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

  19. A facile synthesis of Tenanoparticles with binary size distribution by green chemistry

    Science.gov (United States)

    He, Weidong; Krejci, Alex; Lin, Junhao; Osmulski, Max E.; Dickerson, James H.

    2011-04-01

    Our work reports a facile route to colloidal Tenanocrystals with binary uniform size distributions at room temperature. The binary-sized Tenanocrystals were well separated into two size regimes and assembled into films by electrophoretic deposition. The research provides a new platform for nanomaterials to be efficiently synthesized and manipulated.Our work reports a facile route to colloidal Tenanocrystals with binary uniform size distributions at room temperature. The binary-sized Tenanocrystals were well separated into two size regimes and assembled into films by electrophoretic deposition. The research provides a new platform for nanomaterials to be efficiently synthesized and manipulated. Electronic supplementary information (ESI) available: Synthetic procedures, FTIR analysis, ED pattern, AFM image, and EPD current curve. See DOI: 10.1039/c1nr10025d

  20. 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.

  1. Direct visualization of the interfacial position of colloidal particles and their assemblies

    Science.gov (United States)

    Vogel, N.; Ally, J.; Bley, K.; Kappl, M.; Landfester, K.; Weiss, C. K.

    2014-05-01

    A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply this method to investigate the formation of complex, binary assembly structures directly at the interface, to visualize soft, nanoscale hydrogel colloids in the swollen state, and to visualize and quantify the equilibrium position of individual micro- and nanoscale colloids at the air-water interface depending of the amount of charge present on the particle surface. We find that the degree of deprotonation of the carboxyl group shifts the air-water contact angle, which is further confirmed by colloidal probe atomic force microscopy. Remarkably, the contact angles determined for individual colloidal particles feature a significant distribution that greatly exceeds errors attributable to the size distribution of the colloids. This finding underlines the importance of accessing soft matter on an individual particle level.A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply

  2. Eclipsing binaries in open clusters

    DEFF Research Database (Denmark)

    Southworth, John; Clausen, J.V.

    2006-01-01

    Stars: fundamental parameters - Stars : binaries : eclipsing - Stars: Binaries: spectroscopic - Open clusters and ass. : general Udgivelsesdato: 5 August......Stars: fundamental parameters - Stars : binaries : eclipsing - Stars: Binaries: spectroscopic - Open clusters and ass. : general Udgivelsesdato: 5 August...

  3. Surface roughness directed self-assembly of patchy particles into colloidal micelles.

    Science.gov (United States)

    Kraft, Daniela J; Ni, Ran; Smallenburg, Frank; Hermes, Michiel; Yoon, Kisun; Weitz, David A; van Blaaderen, Alfons; Groenewold, Jan; Dijkstra, Marjolein; Kegel, Willem K

    2012-07-03

    Colloidal particles with site-specific directional interactions, so called "patchy particles", are promising candidates for bottom-up assembly routes towards complex structures with rationally designed properties. Here we present an experimental realization of patchy colloidal particles based on material independent depletion interaction and surface roughness. Curved, smooth patches on rough colloids are shown to be exclusively attractive due to their different overlap volumes. We discuss in detail the case of colloids with one patch that serves as a model for molecular surfactants both with respect to their geometry and their interactions. These one-patch particles assemble into clusters that resemble surfactant micelles with the smooth and attractive sides of the colloids located at the interior. We term these clusters "colloidal micelles". Direct Monte Carlo simulations starting from a homogeneous state give rise to cluster size distributions that are in good agreement with those found in experiments. Important differences with surfactant micelles originate from the colloidal character of our model system and are investigated by simulations and addressed theoretically. Our new "patchy" model system opens up the possibility for self-assembly studies into finite-sized superstructures as well as crystals with as of yet inaccessible structures.

  4. 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

  5. Parametric interactions in presence of different size colloids in semiconductor quantum plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Vanshpal, R., E-mail: ravivanshpal@gmail.com; Sharma, Uttam [Shri Vaishnav Institute of Technology and Science, Indore (India); Dubey, Swati [School of Studies in Physics, Vikram University, Ujjain (M.P.) (India)

    2015-07-31

    Present work is an attempt to investigate the effect of different size colloids on parametric interaction in semiconductor quantum plasma. Inclusion of quantum effect is being done in this analysis through quantum correction term in classical hydrodynamic model of homogeneous semiconductor plasma. The effect is associated with purely quantum origin using quantum Bohm potential and quantum statistics. Colloidal size and quantum correction term modify the parametric dispersion characteristics of ion implanted semiconductor plasma medium. It is found that quantum effect on colloids is inversely proportional to their size. Moreover critical size of implanted colloids for the effective quantum correction is determined which is found to be equal to the lattice spacing of the crystal.

  6. Binary mask programmable hologram.

    Science.gov (United States)

    Tsang, P W M; Poon, T-C; Zhou, Changhe; Cheung, K W K

    2012-11-19

    We report, for the first time, the concept and generation of a novel Fresnel hologram called the digital binary mask programmable hologram (BMPH). A BMPH is comprised of a static, high resolution binary grating that is overlaid with a lower resolution binary mask. The reconstructed image of the BMPH can be programmed to approximate a target image (including both intensity and depth information) by configuring the pattern of the binary mask with a simple genetic algorithm (SGA). As the low resolution binary mask can be realized with less stringent display technology, our method enables the development of simple and economical holographic video display.

  7. Colloid Release from Soil Aggregates

    DEFF Research Database (Denmark)

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

    2012-01-01

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

  8. COLLOID RELEASE FROM DIFFERENT SOIL DEPTH

    Directory of Open Access Journals (Sweden)

    Gang Chen

    2013-01-01

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

  9. Self-Propulsion Mechanism of Active Janus Particles in Near-Critical Binary Mixtures

    NARCIS (Netherlands)

    Samin, Sela; van Roij, Rene

    2015-01-01

    Gold-capped Janus particles immersed in a near-critical binary mixture can be propelled using illumination. We employ a nonisothermal diffuse interface approach to investigate the self-propulsion mechanism of a single colloid. We attribute the motion to body forces at the edges of a micronsized drop

  10. 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.

  11. A short textbook of colloid chemistry

    CERN Document Server

    Jirgensons, B

    1962-01-01

    A Short Textbook of Colloid Chemistry, Second Revised Edition details the factual aspect of colloid chemistry that includes the basic facts, established empirical and mathematical relationships, and practical applications. The chapters of the title are organized into two parts. In the first part, the text discusses the general concepts of colloid chemistry, such as the history and scope, basic terms, and basic methods in experiment with colloids. Part Two covers the technical aspect of colloid chemistry, such as the optical properties, electrical properties, and viscosity. The book will be of

  12. Proteolytic stability in colloidal systems.

    NARCIS (Netherlands)

    Maste, M.C.L.

    1996-01-01

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

  13. Supramolecular perspectives in colloid science

    NARCIS (Netherlands)

    Cohen Stuart, M.A.

    2008-01-01

    Supramolecular chemistry puts emphasis on molecular assemblies held together by non-covalent bonds. As such, it is very close in spirit to colloid science which also focuses on objects which are small, but beyond the molecular scale, and for which other forces than covalent bonds are crucial. We dis

  14. Microbial effects on colloidal agglomeration

    Energy Technology Data Exchange (ETDEWEB)

    Hersman, L.

    1995-11-01

    Colloidal particles are known to enhance the transport of radioactive metals through soil and rock systems. This study was performed to determine if a soil microorganism, isolated from the surface samples collected at Yucca Mountain, NV, could affect the colloidal properties of day particles. The agglomeration of a Wyoming bentonite clay in a sterile uninoculated microbial growth medium was compared to the agglomeration in the medium inoculated with a Pseudomonas sp. In a second experiment, microorganisms were cultured in the succinate medium for 50 h and removed by centrifugation. The agglomeration of the clay in this spent was compared to sterile uninoculated medium. In both experiments, the agglomeration of the clay was greater than that of the sterile, uninoculated control. Based on these results, which indicate that this microorganism enhanced the agglomeration of the bentonite clay, it is possible to say that in the presence of microorganisms colloidal movement through a rock matrix could be reduced because of an overall increase in the size of colloidal particle agglomerates. 32 refs.

  15. Colloidal aspects of texture perception

    NARCIS (Netherlands)

    Vliet, van T.

    2010-01-01

    The perception of complex textures in food is strongly related to the way food is processed during eating, and is modulated by other basic characteristics, such as taste and aroma. An understanding at the colloidal level of the basic processes in the mouth is essential in order to link the compositi

  16. 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.

  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. Interacting binary stars

    CERN Document Server

    Sahade, Jorge; Ter Haar, D

    1978-01-01

    Interacting Binary Stars deals with the development, ideas, and problems in the study of interacting binary stars. The book consolidates the information that is scattered over many publications and papers and gives an account of important discoveries with relevant historical background. Chapters are devoted to the presentation and discussion of the different facets of the field, such as historical account of the development in the field of study of binary stars; the Roche equipotential surfaces; methods and techniques in space astronomy; and enumeration of binary star systems that are studied

  19. Colloidal Photoluminescent Amorphous Porous Silicon, Methods Of Making Colloidal Photoluminescent Amorphous Porous Silicon, And Methods Of Using Colloidal Photoluminescent Amorphous Porous Silicon

    KAUST Repository

    Chaieb, Sahraoui

    2015-04-09

    Embodiments of the present disclosure provide for a colloidal photoluminescent amorphous porous silicon particle suspension, methods of making a colloidal photoluminescent amorphous porous silicon particle suspension, methods of using a colloidal photoluminescent amorphous porous silicon particle suspension, and the like.

  20. 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.

  1. Controlling placement of nonspherical (boomerang) colloids in nematic cells with photopatterned director

    Science.gov (United States)

    Peng, Chenhui; Turiv, Taras; Zhang, Rui; Guo, Yubing; Shiyanovskii, Sergij V.; Wei, Qi-Huo; de Pablo, Juan; Lavrentovich, Oleg D.

    2017-01-01

    Placing colloidal particles in predesigned sites represents a major challenge of the current state-of-the-art colloidal science. Nematic liquid crystals with spatially varying director patterns represent a promising approach to achieve a well-controlled placement of colloidal particles thanks to the elastic forces between the particles and the surrounding landscape of molecular orientation. Here we demonstrate how the spatially varying director field can be used to control placement of non-spherical particles of boomerang shape. The boomerang colloids create director distortions of a dipolar symmetry. When a boomerang particle is placed in a periodic splay-bend director pattern, it migrates towards the region of a maximum bend. The behavior is contrasted to that one of spherical particles with normal surface anchoring, which also produce dipolar director distortions, but prefer to compartmentalize into the regions with a maximum splay. The splay-bend periodic landscape thus allows one to spatially separate these two types of particles. By exploring overdamped dynamics of the colloids, we determine elastic driving forces responsible for the preferential placement. Control of colloidal locations through patterned molecular orientation can be explored for future applications in microfluidic, lab on a chip, sensing and sorting devices.

  2. Photonic crystals, light manipulation, and imaging in complex nematic structures

    Science.gov (United States)

    Ravnik, Miha; Å timulak, Mitja; Mur, Urban; Čančula, Miha; Čopar, Simon; Žumer, Slobodan

    2016-03-01

    Three selected approaches for manipulation of light by complex nematic colloidal and non-colloidal structures are presented using different own custom developed theoretical and modelling approaches. Photonic crystals bands of distorted cholesteric liquid crystal helix and of nematic colloidal opals are presented, also revealing distinct photonic modes and density of states. Light propagation along half-integer nematic disclinations is shown with changes in the light polarization of various winding numbers. As third, simulated light transmission polarization micrographs of nematic torons are shown, offering a new insight into the complex structure characterization. Finally, this work is a contribution towards using complex soft matter in optics and photonics for advanced light manipulation.

  3. Colloidal Plasmonic Titanium Nitride Nanoparticles: Properties and Applications

    Directory of Open Access Journals (Sweden)

    Guler Urcan

    2015-01-01

    Full Text Available Optical properties of colloidal plasmonic titanium nitride nanoparticles are examined with an eye on their photothermal and photocatalytic applications via transmission electron microscopy and optical transmittance measurements. Single crystal titanium nitride cubic nanoparticles with an average size of 50 nm, which was found to be the optimum size for cellular uptake with gold nanoparticles [1], exhibit plasmon resonance in the biological transparency window and demonstrate a high absorption efficiency. A self-passivating native oxide at the surface of the nanoparticles provides an additional degree of freedom for surface functionalization. The titanium oxide shell surrounding the plasmonic core can create new opportunities for photocatalytic applications.

  4. Stable colloids in molten inorganic salts

    Science.gov (United States)

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

    2017-02-01

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

  5. What happens when pharmaceuticals meet colloids.

    Science.gov (United States)

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

    2015-12-01

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

  6. Chancellor Water Colloids: Characterization and Radionuclide Association

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Fattah, Amr I. [Los Alamos National Laboratory

    2012-06-18

    Concluding remarks about this paper are: (1) Gravitational settling, zeta potential, and ultrafiltration data indicate the existence of a colloidal phase of both the alpha and beta emitters in the Chancellor water; (2) The low activity combined with high dispersion homogeneity of the Chancellor water indicate that both alpha and beta emitters are not intrinsic colloids; (3) Radionuclides in the Chancellor water, particularly Pu, coexist as dissolved aqueous and sorbed phases - in other words the radionuclides are partitioned between the aqueous phase and the colloidal phase; (4) The presence of Pu as a dissolved species in the aqueous phase, suggests the possibility of Pu in the (V) oxidation state - this conclusion is supported by the similarity of the k{sub d} value of Pu determined in the current study to that determined for Pu(V) sorbed onto smectite colloids, and the similar electrokinetic behavior of the Chancellor water colloids to smectite colloids; (5) About 50% of the Pu(V) is in the aqueous phase and 50% is sorbed on colloids (mass concentration of colloids in the Chancellor water is 0.12 g/L); (6) The k{sub d} of the Pu and the beta emitters (fission products) between aqueous and colloidal phases in the Chancellor water is {approx}8.0 x 10{sup 3} mL/g using two different activity measurement techniques (LSC and alpha spectroscopy); (7) The gravitational settling and size distributions of the association colloids indicate that the properties (at least the physical ones) of the colloids to which the alpha emitters are associated with seem to be different that the properties of the colloids to which the beta emitters are associated with - the beta emitters are associated with very small particles ({approx}50 - 120 nm), while the alpha emitters are associated with relatively larger particles; and (8) The Chancellor water colloids are extremely stable under the natural pH and ionic strength conditions, indicating high potential for transport in the

  7. Interatomic Potentials for Some Binary Oxides

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Using atomistic computer simulation methods we have derived a new set of interatomic potential parameters for some binary oxides, comprising divalent transition elements (rock-salt structured)and tetrava)ent metals. Computational techniques based on the minimization of the crystal energy with respect to atomic coordinates have been employed. Crystal properties were calculated and compared with the experimental data to check the reliability of our potential models. Intrinsic (Schottky and Frenkel) defect energies were also calculated and compared with previous studies.There is a good agreement between these calculations, which shows that the new potential parameters are reliable and can be used with confidence for future investigations.

  8. Static and dynamic friction in sliding colloidal monolayers

    Science.gov (United States)

    Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2013-03-01

    In a recent experimental breakthrough, the controlled sliding of 2D colloidal crystals over perfectly regular, laser generated periodic or quasi-periodic `corrugation` potentials has been realized in Bechinger's group. Based on realistic MD simulations which reproduce the main experimentally observed features, we explore the potential impact of colloid monolayer sliding in nanotribology. The free motion of edge-spawned kinks and antikinks in smooth incommensurate sliding is contrasted with the kink-antikink pair nucleation at the large static friction threshold in the commensurate case. The Aubry pinning/depinning transition is also demonstrated, e.g., as a function of the corrugation amplitude. Simulated sliding data allow the extraction of frictional work directly from particles coordinates and velocities as a function of classic friction parameters, primarily speed, and corrugation strength. Analogies with sliding charge-density waves, driven Josephson systems, sliding of rare gas islands, and other novel features suggest further experiments and insights, which promote colloid sliding to a novel friction study instrument. Research partly sponsored by Sinergia Project CRSII2 136287/1.

  9. Multidirectional colloidal assembly in concurrent electric and magnetic fields.

    Science.gov (United States)

    Bharti, Bhuvnesh; Kogler, Florian; Hall, Carol K; Klapp, Sabine H L; Velev, Orlin D

    2016-10-07

    Dipolar interactions between nano- and micron sized colloids lead to their assembly into domains with well-defined local order. The particles with a single dipole induced by an external field assemble into linear chains and clusters. However, to achieve the formation of multidirectionally organized nano- or microassemblies with tunable physical characteristics, more sophisticated interaction tools are needed. Here we demonstrate that such complex interactions can be introduced in the form of two independent, non-interacting dipoles (double-dipoles) within a microparticle. We show how this can be achieved by the simultaneous application of alternating current (AC)-electric field and uniform magnetic field to dispersions of superparamagnetic microspheres. Depending on their timing and intensity, concurrent electric and magnetic fields lead to the formation of bidirectional particle chains, colloidal networks, and discrete crystals. We investigate the mechanistic details of the assembly process, and identify and classify the non-equilibrium states formed. The morphologies of different experimental states are in excellent correlation with our theoretical predictions based on Brownian dynamics simulations combined with a structural analysis based on local energy parameters. This novel methodology of introducing and interpreting double-dipolar particle interactions may assist in the assembly of colloidal coatings, dynamically reconfigurable particle networks, and bidirectional active structures.

  10. Interaction of chiral rafts in self-assembled colloidal membranes

    Science.gov (United States)

    Xie, Sheng; Hagan, Michael F.; Pelcovits, Robert A.

    2016-03-01

    Colloidal membranes are monolayer assemblies of rodlike particles that capture the long-wavelength properties of lipid bilayer membranes on the colloidal scale. Recent experiments on colloidal membranes formed by chiral rodlike viruses showed that introducing a second species of virus with different length and opposite chirality leads to the formation of rafts—micron-sized domains of one virus species floating in a background of the other viruses [Sharma et al., Nature (London) 513, 77 (2014), 10.1038/nature13694]. In this article we study the interaction of such rafts using liquid crystal elasticity theory. By numerically minimizing the director elastic free energy, we predict the tilt angle profile for both a single raft and two rafts in a background membrane, and the interaction between two rafts as a function of their separation. We find that the chiral penetration depth in the background membrane sets the scale for the range of the interaction. We compare our results with the experimental data and find good agreement for the strength and range of the interaction. Unlike the experiments, however, we do not observe a complete collapse of the data when rescaled by the tilt angle at the raft edge.

  11. Electrocoagulation of colloidal biogenic selenium.

    Science.gov (United States)

    Staicu, Lucian C; van Hullebusch, Eric D; Lens, Piet N L; Pilon-Smits, Elizabeth A H; Oturan, Mehmet A

    2015-02-01

    Colloidal elemental selenium (Se(0)) adversely affects membrane separation processes and aquatic ecosystems. As a solution to this problem, we investigated for the first time the removal potential of Se(0) by electrocoagulation process. Colloidal Se(0) was produced by a strain of Pseudomonas fluorescens and showed limited gravitational settling. Therefore, iron (Fe) and aluminum (Al) sacrificial electrodes were used in a batch reactor under galvanostatic conditions. The best Se(0) turbidity removal (97 %) was achieved using iron electrodes at 200 mA. Aluminum electrodes removed 96 % of colloidal Se(0) only at a higher current intensity (300 mA). At the best Se(0) removal efficiency, electrocoagulation using Fe electrode removed 93 % of the Se concentration, whereas with Al electrodes the Se removal efficiency reached only 54 %. Due to the less compact nature of the Al flocs, the Se-Al sediment was three times more voluminous than the Se-Fe sediment. The toxicity characteristic leaching procedure (TCLP) test showed that the Fe-Se sediment released Se below the regulatory level (1 mg L(-1)), whereas the Se concentration leached from the Al-Se sediment exceeded the limit by about 20 times. This might be related to the mineralogical nature of the sediments. Electron scanning micrographs showed Fe-Se sediments with a reticular structure, whereas the Al-Se sediments lacked an organized structure. Overall, the results obtained showed that the use of Fe electrodes as soluble anode in electrocoagulation constitutes a better option than Al electrodes for the electrochemical sedimentation of colloidal Se(0).

  12. Thermophoresis of charged colloidal particles.

    Science.gov (United States)

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-04-01

    Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  13. Thermophoresis of charged colloidal particles

    OpenAIRE

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-01-01

    International audience; Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  14. Phase diagrams of binary crystalline-crystalline polymer blends.

    Science.gov (United States)

    Matkar, Rushikesh A; Kyu, Thein

    2006-08-17

    A thermodynamically self-consistent theory has been developed to establish binary phase diagrams for two-crystalline polymer blends by taking into consideration all interactions including amorphous-amorphous, crystal-amorphous, amorphous-crystal, and crystal-crystal interactions. The present theory basically involves combination of the Flory-Huggins free energy for amorphous-amorphous isotropic mixing and the Landau free energy of polymer solidification (e.g., crystallization) of the crystalline constituents. The self-consistent solution via minimization of the free energy of the mixture affords determination of eutectic, peritectic, and azeotrope phase diagrams involving various coexistence regions such as liquid-liquid, liquid-solid, and solid-solid coexistence regions bound by liquidus and solidus lines. To validate the present theory, the predicted eutectic phase diagrams have been compared with the reported experimental binary phase diagrams of blends such as polyethylene fractions as well as polycaprolactone/trioxane mixtures.

  15. Implant materials modified by colloids

    Directory of Open Access Journals (Sweden)

    Zboromirska-Wnukiewicz Beata

    2016-03-01

    Full Text Available Recent advances in general medicine led to the development of biomaterials. Implant material should be characterized by a high biocompatibility to the tissue and appropriate functionality, i.e. to have high mechanical and electrical strength and be stable in an electrolyte environment – these are the most important properties of bioceramic materials. Considerations of biomaterials design embrace also electrical properties occurring on the implant-body fluid interface and consequently the electrokinetic potential, which can be altered by modifying the surface of the implant. In this work, the surface of the implants was modified to decrease the risk of infection by using metal colloids. Nanocolloids were obtained using different chemical and electrical methods. It was found that the colloids obtained by physical and electrical methods are more stable than colloids obtained by chemical route. In this work the surface of modified corundum implants was investigated. The implant modified by nanosilver, obtained by electrical method was selected. The in vivo research on animals was carried out. Clinical observations showed that the implants with modified surface could be applied to wounds caused by atherosclerotic skeleton, for curing the chronic and bacterial inflammations as well as for skeletal reconstruction surgery.

  16. Three-dimensional colloidal lithography

    Science.gov (United States)

    Nagai, Hironori; Poteet, Austen; Zhang, Xu A.; Chang, Chih-Hao

    2017-03-01

    Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle–light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd’s mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.

  17. Three-dimensional colloidal lithography.

    Science.gov (United States)

    Nagai, Hironori; Poteet, Austen; Zhang, Xu A; Chang, Chih-Hao

    2017-03-24

    Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle-light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd's mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.

  18. Colloidal self assembly of non-magnetic particles in magnetic nanofluid

    Energy Technology Data Exchange (ETDEWEB)

    Jadav, Mudra; Patel, Rajesh, E-mail: rjp@mkbhavuni.edu.in, E-mail: rpat7@yahoo.co [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar-364002 (India)

    2015-06-24

    Here we present a technique using magnetic nanofluid to induce bidispersed suspension of nonmagnetic particles to assemble into colloidal chain, triangle, rectangle, ring-flower configurations. By changing the amplitude and direction of the magnetic field, we could tune the structure of nonmagnetic particles in magnetic nanofluid. The structures are assembled using magneto static interactions between effectively nonmagnetic particles dispersed in magnetizable magnetic nanofluid. The assembly of complex structures out of simple colloidal building blocks is of practical interest in photonic crystals and DNA biosensors.

  19. Colloidal self assembly of non-magnetic particles in magnetic nanofluid

    Science.gov (United States)

    Jadav, Mudra; Patel, Rajesh

    2015-06-01

    Here we present a technique using magnetic nanofluid to induce bidispersed suspension of nonmagnetic particles to assemble into colloidal chain, triangle, rectangle, ring-flower configurations. By changing the amplitude and direction of the magnetic field, we could tune the structure of nonmagnetic particles in magnetic nanofluid. The structures are assembled using magneto static interactions between effectively nonmagnetic particles dispersed in magnetizable magnetic nanofluid. The assembly of complex structures out of simple colloidal building blocks is of practical interest in photonic crystals and DNA biosensors.

  20. Janus Nematic Colloids with Designable Valence

    Directory of Open Access Journals (Sweden)

    Simon Čopar

    2014-05-01

    Full Text Available Generalized Janus nematic colloids based on various morphologies of particle surface patches imposing homeotropic and planar surface anchoring are demonstrated. By using mesoscopic numerical modeling, multiple types of Janus particles are explored, demonstrating a variety of novel complex colloidal structures. We also show binding of Janus particles to a fixed Janus post in the nematic cell, which acts as a seed and a micro-anchor for the colloidal structure. Janus colloidal structures reveal diverse topological defect configurations, which are effectively combinations of surface boojum and bulk defects. Topological analysis is applied to defects, importantly showing that topological charge is not a well determined topological invariant in such patchy nematic Janus colloids. Finally, this work demonstrates colloidal structures with designable valence, which could allow for targeted and valence-conditioned self-assembly at micro- and nano-scale.

  1. Crystal lattice optimization and new forms of silicon

    Science.gov (United States)

    Stucke, David P.

    In Chapter 1 a basic outline of the two main methods used in this thesis is given. A genetic algorithm optimization method based on the concept of natural selection is given. The important factors to consider in creating an effective genetic algorithm search are described. I then give a brief overview of Density Functional Theory (DFT) which is the technique most commonly used to do ab-inito calculations on solid-state systems. The basis for its formulation along with how it is applied to a practical system with some approximations is discussed. In Chapter 2 a description of a genetic search algorithm for optimizing the crystal structure of an infinite crystal is given. This method is applied to a system of colloidal spheres, where the packing density is the figure of merit for structure selection. Our examination of self-assembled multi-component crystals of nanoparticles predicts several new structures with stoichiometries of AB (fused spheres), ABC2, ABC 3, ABC4 and AB2 C2. These new structures have hierarchical layered or linear arrangements that could be useful for functional self-assembled systems. For example, the fused-sphere binary crystal assembles with zig-zag rows of parallel nanowires. The genetic search suceeds while a comparable stochastic algorithm fails to find any structures better than the well-known unary or binary phase-separated systems. Here we describe the algorithm and the results it produces: several new classes of binary and ternary crystals of spherical nanoparticles, including a family of layered perovskite-like systems and an unusual three-dimensional array of parallel zig-zag nanowires. In Chapter 3, We discuss the possibility of constructing new forms of silicon by building in multiple bonds consistent with molecules that have been produced experimentally. We find a dilated diamond crystal lattice containing a silicon-silicon triple bond that is metastable. This structure has very soft vibrational modes that are common in similar

  2. Interferometry using binary holograms without high order diffraction effects.

    Science.gov (United States)

    Boruah, Bosanta R; Love, Gordon D; Neil, Mark A A

    2011-06-15

    We describe a technique for a phase-stepping interferometer based on programmable binary phase holograms, particularly useful for optical testing of aspheric or free-form surfaces. It is well-known that binary holograms can be used to generate reference surfaces for interferometry, but a major problem is that cross talk from higher diffraction orders and aliasing can reduce the fidelity of the system. Here, we propose a new encoding technique which improves the accuracy of the technique and demonstrate its implementation using a binary liquid crystal spatial light modulator.

  3. COLLOID RELEASE FROM DIFFERENT SOIL DEPTH

    OpenAIRE

    Gang Chen; Yue Niu; Boya Wang; Kamal Tawfiq

    2013-01-01

    Naturally occurring clay colloidal particles are heavily involved in sediment processes in the subsurface soil. Due to the import ance of these processes in the subsurface environment, the transport of clay colloidal particles has been studied in several disciplines, including soil sciences, petr ology, hydrology, etc. Specifically, in environmental engineering, clay colloid re lease and transport in the sediments have been extensively investigated, which are motiv ated by environmental conce...

  4. Thermophoresis of colloids by mesoscale simulations.

    Science.gov (United States)

    Lüsebrink, Daniel; Yang, Mingcheng; Ripoll, Marisol

    2012-07-18

    The motion of a colloid induced by a temperature gradient is simulated by means of multiparticle collision dynamics, a mesoscale simulation technique. Two algorithms to quantify the thermophoretic behavior are employed and contrasted. The validity of the methods is verified as a function of the temperature gradient, system size, and algorithm parameters. The variation of the solvent-colloid interaction from attractive to purely repulsive interestingly results in the change of the colloid behavior from thermophobic to thermophilic.

  5. Colloidal quantum dots: synthesis, properties and applications

    Science.gov (United States)

    Brichkin, S. B.; Razumov, V. F.

    2016-12-01

    Key recent results obtained in studies of a new class of luminophores, colloidal quantum dots, are analyzed. Modern methods for the synthesis and post-synthetic treatment of colloidal quantum dots that make it possible to achieve record high quantum yield of luminescence and to modify their characteristics for specific applications are considered. Currently important avenues of research on colloidal quantum dots and the problems in and prospects for their practical applications in various fields are discussed. The bibliography includes 272 references.

  6. Engineering of frustration in colloidal artificial ice (Conference Presentation)

    Science.gov (United States)

    Ortiz-Ambriz, Antonio; Tierno, Pietro

    2016-09-01

    Artificial spin-ice systems have been used to date as microscopic models of frustration induced by lattice topology, as they allow for the direct visualization of spin arrangements and textures. However, the engineering of frustrated ice states in which individual spins can be manipulated in situ and the real-time observation of their collective dynamics remain both challenging tasks. Recently, an analogue system has been proposed theoretically, where an optical landscape confined colloidal particles that interacted electrostatically. Here we realize experimentally another version of a colloidal artificial ice system using interacting magnetically polarizable particles confined to lattices of bistable gravitational traps. We show quantitatively that ice-selection rules emerge in this frustrated soft matter system by tuning the strength of the pair-interactions between the microscopic units. By using optical tweezers, we can control particle positioning and dipolar coupling, we introduce monopole-like defects and strings and use loops with defined chirality as an elementary unit to store binary information.

  7. Conductivity maximum in a charged colloidal suspension

    Energy Technology Data Exchange (ETDEWEB)

    Bastea, S

    2009-01-27

    Molecular dynamics simulations of a charged colloidal suspension in the salt-free regime show that the system exhibits an electrical conductivity maximum as a function of colloid charge. We attribute this behavior to two main competing effects: colloid effective charge saturation due to counterion 'condensation' and diffusion slowdown due to the relaxation effect. In agreement with previous observations, we also find that the effective transported charge is larger than the one determined by the Stern layer and suggest that it corresponds to the boundary fluid layer at the surface of the colloidal particles.

  8. Synthesis and Analytical Centrifugation of Magnetic Model Colloids

    OpenAIRE

    Luigjes, B.

    2012-01-01

    This thesis is a study of the preparation and thermodynamic properties of magnetic colloids. First, two types of magnetic model colloids are investigated: composite colloids and single-domain nanoparticles. Thermodynamics of magnetic colloids is studied using analytical centrifugation, including a specially adapted centrifuge for measuring heavy and strongly light absorbing colloids. Magnetic composite colloids can be prepared from thermodynamically stable Pickering emulsions of 3-methacrylox...

  9. 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

  10. Direct Measurements of Island Growth and Step-Edge Barriers in Colloidal Epitaxy

    KAUST Repository

    Ganapathy, R.

    2010-01-21

    Epitaxial growth, a bottom-up self-assembly process for creating surface nano- and microstructures, has been extensively studied in the context of atoms. This process, however, is also a promising route to self-assembly of nanometer- and micrometer-scale particles into microstructures that have numerous technological applications. To determine whether atomic epitaxial growth laws are applicable to the epitaxy of larger particles with attractive interactions, we investigated the nucleation and growth dynamics of colloidal crystal films with single-particle resolution. We show quantitatively that colloidal epitaxy obeys the same two-dimensional island nucleation and growth laws that govern atomic epitaxy. However, we found that in colloidal epitaxy, step-edge and corner barriers that are responsible for film morphology have a diffusive origin. This diffusive mechanism suggests new routes toward controlling film morphology during epitaxy.

  11. 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.

  12. 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.

  13. Fabrication of photonic crystals with nigrosine-doped poly(MMA-co-DVB-co-MAA) particles.

    Science.gov (United States)

    Zhang, Shuai; Zhao, Xiang-Wei; Xu, Hua; Zhu, Rong; Gu, Zhong-Ze

    2007-12-01

    A convenient approach was developed to fabricate monodisperse nigrosine-doped poly(methyl methacrylate-co-divinylbenzene-co-methacrylic acid) nanoparticles with different cross-linkage by soap-free emulsion polymerization at boiling status and swelling process. The dye-doped nanoparticles were used for the fabrication of colloidal crystal films and beads. It was found that nigrosine dye in the nanoparticles can efficiently depress the light scattering inside the colloidal crystal films and eliminate the iridescent effect in the photonic beads. These results make the colloidal crystals useful in photonic paper, bioassay, and so on.

  14. Photophysics of C60 Colloids

    Science.gov (United States)

    2012-11-28

    34Investigation of encapsulation and solvatochromism of fullerenes in binary solvent mixtures," Journal of Physical Chemistry B 103(51), 11256-11260 (1999). 76...E. Huie, P. Neta, H. Hungerbühler, and K.-D. Asmus, "Excitation of C60, solubilized in water by triton X-100 and [gamma]- cyclodextrin , and

  15. The hydrodynamics of colloidal gelation.

    Science.gov (United States)

    Varga, Zsigmond; Wang, Gang; Swan, James

    2015-12-14

    Colloidal gels are formed during arrested phase separation. Sub-micron, mutually attractive particles aggregate to form a system spanning network with high interfacial area, far from equilibrium. Models for microstructural evolution during colloidal gelation have often struggled to match experimental results with long standing questions regarding the role of hydrodynamic interactions. In nearly all models, these interactions are neglected entirely. In the present work, we report simulations of gelation with and without hydrodynamic interactions between the suspended particles executed in HOOMD-blue. The disparities between these simulations are striking and mirror the experimental-theoretical mismatch in the literature. The hydrodynamic simulations agree with experimental observations, however. We explore a simple model of the competing transport processes in gelation that anticipates these disparities, and conclude that hydrodynamic forces are essential. Near the gel boundary, there exists a competition between compaction of individual aggregates which suppresses gelation and coagulation of aggregates which enhances it. The time scale for compaction is mildly slowed by hydrodynamic interactions, while the time scale for coagulation is greatly accelerated. This enhancement to coagulation leads to a shift in the gel boundary to lower strengths of attraction and lower particle concentrations when compared to models that neglect hydrodynamic interactions. Away from the gel boundary, differences in the nearest neighbor distribution and fractal dimension persist within gels produced by both simulation methods. This result necessitates a fundamental rethinking of how dynamic, discrete element models for gelation kinetics are developed as well as how collective hydrodynamic interactions influence the arrest of attractive colloidal dispersions.

  16. Structural color from colloidal glasses

    Science.gov (United States)

    Magkiriadou, Sofia

    When a material has inhomogeneities at a lengthscale comparable to the wavelength of light, interference can give rise to structural colors: colors that originate from the interaction of the material's microstructure with light and do not require absorbing dyes. In this thesis we study a class of these materials, called photonic glasses, where the inhomogeneities form a dense and random arrangement. Photonic glasses have angle-independent structural colors that look like those of conventional dyes. However, when this work started, there was only a handful of colors accessible with photonic glasses, mostly hues of blue. We use various types of colloidal particles to make photonic glasses, and we study, both theoretically and experimentally, how the optical properties of these glasses relate to their structure and constituent particles. Based on our observations from glasses of conventional particles, we construct a theoretical model that explains the scarcity of yellow, orange, and red photonic glasses. Guided by this model, we develop novel colloidal systems that allow a higher degree of control over structural color. We assemble glasses of soft, core-shell particles with scattering cores and transparent shells, where the resonant wavelength can be tuned independently of the reflectivity. We then encapsulate glasses of these core-shell particles into emulsion droplets of tunable size; in this system, we observe, for the first time, angle-independent structural colors that cover the entire visible spectrum. To enhance color saturation, we begin experimenting with inverse glasses, where the refractive index of the particles is lower than the refractive index of the medium, with promising results. Finally, based on our theoretical model for scattering from colloidal glasses, we begin an exploration of the color gamut that could be achieved with this technique, and we find that photonic glasses are a promising approach to a new type of long-lasting, non-toxic, and

  17. Kuiper Binary Object Formation

    CERN Document Server

    Nazzario, R C; Covington, C; Kagan, D; Hyde, T W

    2005-01-01

    It has been observed that binary Kuiper Belt Objects (KBOs) exist contrary to theoretical expectations. Their creation presents problems to most current models. However, the inclusion of a third body (for example, one of the outer planets) may provide the conditions necessary for the formation of these objects. The presence of a third massive body not only helps to clear the primordial Kuiper Belt but can also result in long lived binary Kuiper belt objects. The gravitational interaction between the KBOs and the third body causes one of four effects; scattering into the Oort cloud, collisions with the growing protoplanets, formation of binary pairs, or creation of a single Kuiper belt object. Additionally, the initial location of the progenitors of the Kuiper belt objects also has a significant effect on binary formation.

  18. 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

  19. Frost Heave in Colloidal Soils

    KAUST Repository

    Peppin, Stephen

    2011-01-01

    We develop a mathematical model of frost heave in colloidal soils. The theory accountsfor heave and consolidation while not requiring a frozen fringe assumption. Two solidificationregimes occur: a compaction regime in which the soil consolidates to accommodate the ice lenses, and a heave regime during which liquid is sucked into the consolidated soil from an external reservoir, and the added volume causes the soil to heave. The ice fraction is found to vary inversely with thefreezing velocity V , while the rate of heave is independent of V , consistent with field and laboratoryobservations. © 2011 Society for Industrial and Applied Mathematics.

  20. Structured fluids polymers, colloids, surfactants

    CERN Document Server

    Witten, Thomas A

    2010-01-01

    Over the last thirty years, the study of liquids containing polymers, surfactants, or colloidal particles has developed from a loose assembly of facts into a coherent discipline with substantial predictive power. These liquids expand our conception of what condensed matter can do. Such structured-fluid phenomena dominate the physical environment within living cells. This book teaches how to think of these fluids from a unified point of view showing the far-reaching effects ofthermal fluctuations in producing forces and motions. Keeping mathematics to a minimum, the book seeks the simplest expl

  1. Kuiper Binary Object Formation

    OpenAIRE

    Nazzario, R. C.; Orr, K.; Covington, C.; Kagan, D.; Hyde, T. W.

    2005-01-01

    It has been observed that binary Kuiper Belt Objects (KBOs) exist contrary to theoretical expectations. Their creation presents problems to most current models. However, the inclusion of a third body (for example, one of the outer planets) may provide the conditions necessary for the formation of these objects. The presence of a third massive body not only helps to clear the primordial Kuiper Belt but can also result in long lived binary Kuiper belt objects. The gravitational interaction betw...

  2. Colloidal iron(III) pyrophosphate particles

    NARCIS (Netherlands)

    Rossi, L.; Velikov, K. P.; Philipse, A.P.

    2014-01-01

    Ferric pyrophosphate is a widely used material in the area of mineral fortification but its synthesis and properties in colloidal form are largely unknown. In this article, we report on the synthesis and characterisation of colloidal iron(III) pyrophosphate particles with potential for application a

  3. Lattice density functional for colloid-polymer mixtures: Comparison of two fundamental measure theories

    Science.gov (United States)

    Cuesta, José A.; Lafuente, Luis; Schmidt, Matthias

    2005-09-01

    We consider a binary mixture of colloid and polymer particles with positions on a simple cubic lattice. Colloids exclude both colloids and polymers from nearest neighbor sites. Polymers are treated as effective particles that are mutually noninteracting, but exclude colloids from neighboring sites; this is a discrete version of the (continuum) Asakura-Oosawa-Vrij model. Two alternative density functionals are proposed and compared in detail. The first is based on multioccupancy in the zero-dimensional limit of the bare model, analogous to the corresponding continuum theory that reproduces the bulk fluid free energy of free volume theory. The second is based on mapping the polymers onto a multicomponent mixture of polymer clusters that are shown to behave as hard cores; the corresponding property of the extended model in strong confinement permits direct treatment with lattice fundamental measure theory. Both theories predict the same topology for the phase diagram with a continuous fluid-fcc freezing transition at low polymer fugacity and, upon crossing a tricritical point, a first-order freezing transition for high polymer fugacities with rapidly broadening density jump.

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

    Science.gov (United States)

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

    2015-11-01

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

  5. Eclipsing Binary Pulsars

    CERN Document Server

    Freire, P C C

    2004-01-01

    The first eclipsing binary pulsar, PSR B1957+20, was discovered in 1987. Since then, 13 other eclipsing low-mass binary pulsars have been found, 12 of these are in globular clusters. In this paper we list the known eclipsing binary pulsars and their properties, with special attention to the eclipsing systems in 47 Tuc. We find that there are two fundamentally different groups of eclipsing binary pulsars; separated by their companion masses. The less massive systems (M_c ~ 0.02 M_sun) are a product of predictable stellar evolution in binary pulsars. The systems with more massive companions (M_c ~ 0.2 M_sun) were formed by exchange encounters in globular clusters, and for that reason are exclusive to those environments. This class of systems can be used to learn about the neutron star recycling fraction in the globular clusters actively forming pulsars. We suggest that most of these binary systems are undetectable at radio wavelengths.

  6. Coupled parametric processes in binary nonlinear photonic structures

    CERN Document Server

    Saygin, M Yu

    2016-01-01

    We study parametric interactions in a new type of nonlinear photonic structures, which is realized in the vicinity of a pair of nonlinear crystals. In this kind of structure, which we call binary, multiple nonlinear optical processes can be implemented simultaneously, owing to multiple phase-matching conditions, fulfilled separately in the constituent crystals. The coupling between the nonlinear processes by means of modes sharing similar frequency is attained by the spatially-broadband nature of the parametric fields. We investigate the spatial properties of the fields generated in the binary structure constructed from periodically poled crystals for the two examples: 1) single parametric down-conversion, and 2) coupled parametric down-conversion and up-conversion processes. The efficacy of the fields' generation in these examples is analyzed through comparison with the cases of traditional single periodically poled crystal and aperiodic photonic structure, respectively. It has been shown that the relative s...

  7. Diffusion in active magnetic colloids

    Energy Technology Data Exchange (ETDEWEB)

    Taukulis, R.; Cebers, A., E-mail: aceb@tesla.sal.lv

    2014-11-15

    Properties of active colloids of circle swimmers are reviewed. As a particular example of active magnetic colloids the magnetotactic bacteria under the action of a rotating magnetic field is considered. The relation for a diffusion coefficient due to the random switching of the direction of rotation of their rotary motors is derived on the basis of the master equation. The obtained relation is confirmed by the direct numerical simulation of random trajectory of a magnetotactic bacterium under the action of the Poisson type internal noise due to the random switching of rotary motors. The results obtained are in qualitative and quantitative agreement with the available experimental results and allow one to determine the characteristic time between the switching events of a rotary motor of the bacterium. - Highlights: • Magnetotactic bacteria in a rotating field behaves as circle swimmers. • Diffusion coefficient of these swimmers due to the random switching of rotary motors is calculated. • Results are in good qualitative and quantitative agreement with available experimental results.

  8. 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.

  9. 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.

  10. 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

  11. Soft matter perspective on protein crystal assembly.

    Science.gov (United States)

    Fusco, Diana; Charbonneau, Patrick

    2016-01-01

    Crystallography may be the gold standard of protein structure determination, but obtaining the necessary high-quality crystals is also in some ways akin to prospecting for the precious metal. The tools and models developed in soft matter physics to understand colloidal assembly offer some insights into the problem of crystallizing proteins. This topical review describes the various analogies that have been made between proteins and colloids in that context. We highlight the explanatory power of patchy particle models, but also the challenges of providing guidance for crystallizing specific proteins. We conclude with a presentation of possible future research directions. This review is intended for soft matter scientists interested in protein crystallization as a self-assembly problem, and as an introduction to the pertinent physics literature for protein scientists more generally.

  12. 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.

  13. Nanoscopic Manipulation and Imaging of Liquid Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Rosenblatt, Charles S. [Case Western Reserve Univ., Cleveland, OH (United States)

    2014-02-04

    This is the final project report. The project’s goals centered on nanoscopic imaging and control of liquid crystals and surfaces. We developed and refined techniques to control liquid crystal orientation at surfaces with resolution as small as 25 nm, we developed an optical imaging technique that we call Optical Nanotomography that allows us to obtain images inside liquid crystal films with resolution of 60 x 60 x 1 nm, and we opened new thrust areas related to chirality and to liquid crystal/colloid composites.

  14. Stoichiometric control of DNA-grafted colloid self-assembly.

    Science.gov (United States)

    Vo, Thi; Venkatasubramanian, Venkat; Kumar, Sanat; Srinivasan, Babji; Pal, Suchetan; Zhang, Yugang; Gang, Oleg

    2015-04-21

    There has been considerable interest in understanding the self-assembly of DNA-grafted nanoparticles into different crystal structures, e.g., CsCl, AlB2, and Cr3Si. Although there are important exceptions, a generally accepted view is that the right stoichiometry of the two building block colloids needs to be mixed to form the desired crystal structure. To incisively probe this issue, we combine experiments and theory on a series of DNA-grafted nanoparticles at varying stoichiometries, including noninteger values. We show that stoichiometry can couple with the geometries of the building blocks to tune the resulting equilibrium crystal morphology. As a concrete example, a stoichiometric ratio of 3:1 typically results in the Cr3Si structure. However, AlB2 can form when appropriate building blocks are used so that the AlB2 standard-state free energy is low enough to overcome the entropic preference for Cr3Si. These situations can also lead to an undesirable phase coexistence between crystal polymorphs. Thus, whereas stoichiometry can be a powerful handle for direct control of lattice formation, care must be taken in its design and selection to avoid polymorph coexistence.

  15. Goethite liquid crystals and magnetic field effects

    NARCIS (Netherlands)

    van den Pol, E

    2010-01-01

    In this thesis the liquid crystal phase behavior of colloidal, boardlike, goethite (alpha-FeOOH) particles is described. Apart from the nematic phase, a smectic A phase is formed in systems with a low and high polydispersity. Strong fractionation occurs which is able to reduce the local length polyd

  16. Fabrication and Analysis of Photonic Crystals

    Science.gov (United States)

    Campbell, Dean J.; Korte, Kylee E.; Xia, Younan

    2007-01-01

    These laboratory experiments are designed to explore aspects of nanoscale chemistry by constructing and spectroscopically analyzing thin films of photonic crystals. Films comprised of colloidal spheres and polydimethylsiloxane exhibit diffraction-based stop bands that shift reversibly upon exposure to some common solvents. Topics covered in these…

  17. Binary Masking & Speech Intelligibility

    DEFF Research Database (Denmark)

    Boldt, Jesper

    The purpose of this thesis is to examine how binary masking can be used to increase intelligibility in situations where hearing impaired listeners have difficulties understanding what is being said. The major part of the experiments carried out in this thesis can be categorized as either experime...... mask using a directional system and a method for correcting errors in the target binary mask. The last part of the thesis, proposes a new method for objective evaluation of speech intelligibility.......The purpose of this thesis is to examine how binary masking can be used to increase intelligibility in situations where hearing impaired listeners have difficulties understanding what is being said. The major part of the experiments carried out in this thesis can be categorized as either...... experiments under ideal conditions or as experiments under more realistic conditions useful for real-life applications such as hearing aids. In the experiments under ideal conditions, the previously defined ideal binary mask is evaluated using hearing impaired listeners, and a novel binary mask -- the target...

  18. Skewed Binary Search Trees

    DEFF Research Database (Denmark)

    Brodal, Gerth Stølting; Moruz, Gabriel

    2006-01-01

    It is well-known that to minimize the number of comparisons a binary search tree should be perfectly balanced. Previous work has shown that a dominating factor over the running time for a search is the number of cache faults performed, and that an appropriate memory layout of a binary search tree...... can reduce the number of cache faults by several hundred percent. Motivated by the fact that during a search branching to the left or right at a node does not necessarily have the same cost, e.g. because of branch prediction schemes, we in this paper study the class of skewed binary search trees....... For all nodes in a skewed binary search tree the ratio between the size of the left subtree and the size of the tree is a fixed constant (a ratio of 1/2 gives perfect balanced trees). In this paper we present an experimental study of various memory layouts of static skewed binary search trees, where each...

  19. Binary Neutron Star Mergers

    Directory of Open Access Journals (Sweden)

    Joshua A. Faber

    2012-07-01

    Full Text Available We review the current status of studies of the coalescence of binary neutron star systems. We begin with a discussion of the formation channels of merging binaries and we discuss the most recent theoretical predictions for merger rates. Next, we turn to the quasi-equilibrium formalisms that are used to study binaries prior to the merger phase and to generate initial data for fully dynamical simulations. The quasi-equilibrium approximation has played a key role in developing our understanding of the physics of binary coalescence and, in particular, of the orbital instability processes that can drive binaries to merger at the end of their lifetimes. We then turn to the numerical techniques used in dynamical simulations, including relativistic formalisms, (magneto-hydrodynamics, gravitational-wave extraction techniques, and nuclear microphysics treatments. This is followed by a summary of the simulations performed across the field to date, including the most recent results from both fully relativistic and microphysically detailed simulations. Finally, we discuss the likely directions for the field as we transition from the first to the second generation of gravitational-wave interferometers and while supercomputers reach the petascale frontier.

  20. Phosphate binding by natural iron-rich colloids in streams

    NARCIS (Netherlands)

    Baken, S.; Moens, C.; Griffioen, J.J.; Smolders, E.

    2016-01-01

    Phosphorus (P) in natural waters may be bound to iron (Fe) bearing colloids. However, the natural variation in composition and P binding strength of these colloids remain unclear. We related the composition of "coarse colloids" (colloids in the 0.1-1.2 μm size range) in 47 Belgian streams to the che

  1. Synthesis and Analytical Centrifugation of Magnetic Model Colloids

    NARCIS (Netherlands)

    Luigjes, B.

    2012-01-01

    This thesis is a study of the preparation and thermodynamic properties of magnetic colloids. First, two types of magnetic model colloids are investigated: composite colloids and single-domain nanoparticles. Thermodynamics of magnetic colloids is studied using analytical centrifugation, including a s

  2. Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

    Science.gov (United States)

    Wen, Liang-Saw; Santschi, Peter H.; Tang, Degui

    1997-07-01

    It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority (>50%) of the colloidal trace metals had been transferred into the particulate phase (≥0.45 μm), except for 65Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe (˜60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of 59Fe and 110Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of 54Mn, 133Ba, 65Zn, 109Cd, 113Sn, and 60CO increased while the LMW (≤ 1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The values of the particle-water ( Kd) and colloid-water partitioning ( Kc) coefficients for most trace metals were similar to those observed in Galveston Bay waters, suggesting complementary results to field studies. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying

  3. Analytical solutions for elastic binary nanotubes of arbitrary chirality

    Science.gov (United States)

    Jiang, Lai; Guo, Wanlin

    2016-09-01

    Analytical solutions for the elastic properties of a variety of binary nanotubes with arbitrary chirality are obtained through the study of systematic molecular mechanics. This molecular mechanics model is first extended to chiral binary nanotubes by introducing an additional out-of-plane inversion term into the so-called stick-spiral model, which results from the polar bonds and the buckling of binary graphitic crystals. The closed-form expressions for the longitudinal and circumferential Young's modulus and Poisson's ratio of chiral binary nanotubes are derived as functions of the tube diameter. The obtained inversion force constants are negative for all types of binary nanotubes, and the predicted tube stiffness is lower than that by the former stick-spiral model without consideration of the inversion term, reflecting the softening effect of the buckling on the elastic properties of binary nanotubes. The obtained properties are shown to be comparable to available density functional theory calculated results and to be chirality and size sensitive. The developed model and explicit solutions provide a systematic understanding of the mechanical performance of binary nanotubes consisting of III-V and II-VI group elements.

  4. Analytical solutions for elastic binary nanotubes of arbitrary chirality

    Science.gov (United States)

    Jiang, Lai; Guo, Wanlin

    2016-12-01

    Analytical solutions for the elastic properties of a variety of binary nanotubes with arbitrary chirality are obtained through the study of systematic molecular mechanics. This molecular mechanics model is first extended to chiral binary nanotubes by introducing an additional out-of-plane inversion term into the so-called stick-spiral model, which results from the polar bonds and the buckling of binary graphitic crystals. The closed-form expressions for the longitudinal and circumferential Young's modulus and Poisson's ratio of chiral binary nanotubes are derived as functions of the tube diameter. The obtained inversion force constants are negative for all types of binary nanotubes, and the predicted tube stiffness is lower than that by the former stick-spiral model without consideration of the inversion term, reflecting the softening effect of the buckling on the elastic properties of binary nanotubes. The obtained properties are shown to be comparable to available density functional theory calculated results and to be chirality and size sensitive. The developed model and explicit solutions provide a systematic understanding of the mechanical performance of binary nanotubes consisting of III-V and II-VI group elements.

  5. Binary and Millisecond Pulsars

    Directory of Open Access Journals (Sweden)

    Lorimer Duncan R.

    2008-11-01

    Full Text Available We review the main properties, demographics and applications of binary and millisecond radio pulsars. Our knowledge of these exciting objects has greatly increased in recent years, mainly due to successful surveys which have brought the known pulsar population to over 1800. There are now 83 binary and millisecond pulsars associated with the disk of our Galaxy, and a further 140 pulsars in 26 of the Galactic globular clusters. Recent highlights include the discovery of the young relativistic binary system PSR J1906+0746, a rejuvination in globular cluster pulsar research including growing numbers of pulsars with masses in excess of 1.5M_⊙, a precise measurement of relativistic spin precession in the double pulsar system and a Galactic millisecond pulsar in an eccentric (e = 0.44 orbit around an unevolved companion.

  6. Binary Popldation Synthcsis Study

    Institute of Scientific and Technical Information of China (English)

    HAN Zhanwen

    2011-01-01

    Binary population synthesis (BPS), an approach to evolving millions of stars (including binaries) simultaneously, plays a crucial role in our understanding of stellar physics, the structure and evolution of galaxies, and cosmology. We proposed and developed a BPS approach, and used it to investigate the formation of many peculiar stars such as hot subdwarf stars, progenitors of type la supernovae, barium stars, CH stars, planetary nebulae, double white dwarfs, blue stragglers, contact binaries, etc. We also established an evolution population synthesis (EPS) model, the Yunnan Model, which takes into account binary interactions for the first time. We applied our model for the origin of hot subdwarf stars in the study of elliptical galaxies and explained their far-UV radiation.

  7. Carbon Nanomaterials as Antibacterial Colloids

    Directory of Open Access Journals (Sweden)

    Michael Maas

    2016-07-01

    Full Text Available Carbon nanomaterials like graphene, carbon nanotubes, fullerenes and the various forms of diamond have attracted great attention for their vast potential regarding applications in electrical engineering and as biomaterials. The study of the antibacterial properties of carbon nanomaterials provides fundamental information on the possible toxicity and environmental impact of these materials. Furthermore, as a result of the increasing prevalence of resistant bacteria strains, the development of novel antibacterial materials is of great importance. This article reviews current research efforts on characterizing the antibacterial activity of carbon nanomaterials from the perspective of colloid and interface science. Building on these fundamental findings, recent functionalization strategies for enhancing the antibacterial effect of carbon nanomaterials are described. The review concludes with a comprehensive outlook that summarizes the most important discoveries and trends regarding antibacterial carbon nanomaterials.

  8. 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

    -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......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...... 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...

  9. Colloid and interface chemistry for nanotechnology

    CERN Document Server

    Kralchevsky, Peter

    2013-01-01

    Colloid and interface science dealt with nanoscale objects for nearly a century before the term nanotechnology was coined. An interdisciplinary field, it bridges the macroscopic world and the small world of atoms and molecules. Colloid and Interface Chemistry for Nanotechnology is a collection of manuscripts reflecting the activities of research teams that have been involved in the networking project Colloid and Interface Chemistry for Nanotechnology (2006-2011), Action D43, the European Science Foundation. The project was a part of the intergovernmental framework for Cooperation in Science an

  10. Realistic calculation of the low- and high-density liquid phase separation in a charged colloidal dispersion

    Science.gov (United States)

    Lai, S. K.; Peng, W. P.; Wang, G. F.

    2001-04-01

    A realistic statistical-mechanics model is applied to describe the repulsive interaction between charged colloids. The latter, in combination with the long-range van der Waals attraction simulated under excess salt environment, gives rise to a total intercolloidal particle potential showing a clear second potential minimum. Differing from the usual Derjaguin-Landau-Verwey-Overbeek (DLVO) model, the present model is valid at any finite concentration of colloids and is thus an appropriate model for investigating the low- and high-density liquid phase transition. Employing this two-body colloid-colloid potential and in conjunction with the Weeks-Chandler-Andersen [J. D. Weeks, D. Chandler, and H. C. Andersen, J. Chem. Phys. 54, 5237 (1971)] thermodynamic perturbation theory, we derive analytical expressions for the pressure, chemical potential, and related thermodynamic functions. These thermodynamic quantities were used to calculate the phase diagrams of charged colloidal dispersions in terms of the critical parameters: temperature, volume fraction, and electrolyte concentration parameter kD. Compared with the DLVO model, we find the areas enclosed within the spinodal decomposition and also the liquid-liquid coexistence curves broader in the present model for an excess salt condition κ=kDσ0300, the disparities between the two models reduce. The same thermodynamic perturbation theory has been employed to study also the weak reversible coagulation whose physical origin is attributed to the presence of the second potential minimum. We examine various colloidal parameters that affect the structure of the latter and deduce from our analysis the conditions of colloidal stability. In comparison with the measured flocculation data for a binary mixture of polystyrene lattices and water, we find that our calculated results are generally reasonable, thus lending great credence to the presently used model.

  11. Eclipsing Binary Update, No. 2.

    Science.gov (United States)

    Williams, D. B.

    1996-01-01

    Contents: 1. Wrong again! The elusive period of DHK 41. 2. Stars observed and not observed. 3. Eclipsing binary chart information. 4. Eclipsing binary news and notes. 5. A note on SS Arietis. 6. Featured star: TX Ursae Majoris.

  12. A Course in Colloid and Surface Science.

    Science.gov (United States)

    Scamehorn, John F.

    1984-01-01

    Describes a course for chemical engineers, chemists, and petroleum engineers that focuses on colloid and surface science. Major topic areas in the course include capillarity, surface thermodynamics, adsorption contact angle, micelle formation, solubilization in micelles, emulsions, foams, and applications. (JN)

  13. 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

  14. Suspensions of colloidal particles and aggregates

    CERN Document Server

    Babick, Frank

    2016-01-01

    This book addresses the properties of particles in colloidal suspensions. It has a focus on particle aggregates and the dependency of their physical behaviour on morphological parameters. For this purpose, relevant theories and methodological tools are reviewed and applied to selected examples. The book is divided into four main chapters. The first of them introduces important measurement techniques for the determination of particle size and interfacial properties in colloidal suspensions. A further chapter is devoted to the physico-chemical properties of colloidal particles—highlighting the interfacial phenomena and the corresponding interactions between particles. The book’s central chapter examines the structure-property relations of colloidal aggregates. This comprises concepts to quantify size and structure of aggregates, models and numerical tools for calculating the (light) scattering and hydrodynamic properties of aggregates, and a discussion on van-der-Waals and double layer interactions between ...

  15. Size determinations of colloidal fat emulsions

    DEFF Research Database (Denmark)

    Kuntsche, Judith; Klaus, Katrin; Steiniger, Frank

    2009-01-01

    Size and size distributions of colloidal dispersions are of crucial importance for their performance and safety. In the present study, commercially available fat emulsions (Lipofundin N, Lipofundin MCT and Lipidem) were analyzed by photon correlation spectroscopy, laser diffraction with adequate...

  16. Enhanced and preferential optical trapping in a slot-graphite photonic crystal (Conference Presentation)

    Science.gov (United States)

    Krishnan, Aravind; Povinelli, Michelle L.; Wu, Shao-Hua; Huang, Ningfeng

    2016-09-01

    Optical trapping serves as a powerful tool for the manipulation of matter on the nanoscale and ultra-precise measurement of weak forces. However, the applicability of these tools is limited by the available laser power and trap efficiency. We utilized the strong confinement of light in a slot-graphite photonic crystal to develop high-efficiency parallel trapping over a large area. The stiffness is several orders of magnitude higher than conventional optical tweezers and two orders of magnitude higher than our previously demonstrated on-chip, near field traps. We demonstrate the ability to trap both dielectric and metallic nanoparticles of sub-micron size. We find that the growth kinetics of nanoparticle arrays on the slot-graphite template depends on particle size. Smaller particles diffuse more, more readily occupying the available trap sites and inhibiting the trapping of larger particles. Smaller particles also sink more into the holes in the photonic crystal, resulting in stronger mechanical confinement and a deeper potential well. We use these differences to selectively trap one type of particle out of a binary colloidal mixture, creating an efficient optical sieve. This technique has rich potential in the fields of trace analysis, optical diagnostics, and enrichment and sorting of microscopic entities and molecules.

  17. Stabilising emulsion-based colloidal structures with mixed food ingredients.

    Science.gov (United States)

    Dickinson, Eric

    2013-03-15

    The physical scientist views food as a complex form of soft matter. The complexity has its origin in the numerous ingredients that are typically mixed together and the subtle variations in microstructure and texture induced by thermal and mechanical processing. The colloid science approach to food product formulation is based on the assumption that the major product attributes such as appearance, rheology and physical stability are determined by the spatial distribution and interactions of a small number of generic structural entities (biopolymers, particles, droplets, bubbles, crystals) organised in various kinds of structural arrangements (layers, complexes, aggregates, networks). This review describes some recent advances in this field with reference to three discrete classes of dispersed systems: particle-stabilised emulsions, emulsion gels and aerated emulsions. Particular attention is directed towards explaining the crucial role of the macromolecular ingredients (proteins and polysaccharides) in controlling the formation and stabilisation of the colloidal structures. The ultimate objective of this research is to provide the basic physicochemical insight required for the reliable manufacture of novel structured foods with an appealing taste and texture, whilst incorporating a more healthy set of ingredients than those found in many existing traditional products.

  18. Structural Color Patterns by Electrohydrodynamic Jet Printed Photonic Crystals.

    Science.gov (United States)

    Ding, Haibo; Zhu, Cun; Tian, Lei; Liu, Cihui; Fu, Guangbin; Shang, Luoran; Gu, Zhongze

    2017-02-09

    In this work, we demonstrate the fabrication of photonic crystal patterns with controllable morphologies and structural colors utilizing electrohydrodynamic jet (E-jet) printing with colloidal crystal inks. The final shape of photonic crystal units is controlled by the applied voltage signal and wettability of the substrate. Optical properties of the structural color patterns are tuned by the self-assembly of the silica nanoparticle building blocks. Using this direct printing technique, it is feasible to print customized functional patterns composed of photonic crystal dots or photonic crystal lines according to relevant printing mode and predesigned tracks. This is the first report for E-jet printing with colloidal crystal inks. Our results exhibit promising applications in displays, biosensors, and other functional devices.

  19. Compressing Binary Decision Diagrams

    DEFF Research Database (Denmark)

    Hansen, Esben Rune; Satti, Srinivasa Rao; Tiedemann, Peter

    2008-01-01

    The paper introduces a new technique for compressing Binary Decision Diagrams in those cases where random access is not required. Using this technique, compression and decompression can be done in linear time in the size of the BDD and compression will in many cases reduce the size of the BDD to 1...

  20. Compressing Binary Decision Diagrams

    DEFF Research Database (Denmark)

    Rune Hansen, Esben; Srinivasa Rao, S.; Tiedemann, Peter

    The paper introduces a new technique for compressing Binary Decision Diagrams in those cases where random access is not required. Using this technique, compression and decompression can be done in linear time in the size of the BDD and compression will in many cases reduce the size of the BDD to 1...

  1. Orbits for sixteen binaries

    Directory of Open Access Journals (Sweden)

    Cvetković Z.

    2006-01-01

    Full Text Available In this paper orbits for 13 binaries are recalculated and presented. The reason is that recent observations show higher residuals than the corresponding ephemerides calculated by using the orbital elements given in the Sixth Catalog of Orbits of Visual Binary Stars. The binaries studied were: WDS 00182+7257 = A 803, WDS 00335+4006 = HO 3, WDS 00583+2124 = BU 302, WDS 01011+6022 = A 926, WDS 01014+1155 = BU 867, WDS 01112+4113 = A 655, WDS 01361−2954 + HJ 3447, WDS 02333+5219 = STT 42 AB,WDS 04362+0814 = A 1840 AB,WDS 08017−0836 = A 1580, WDS 08277−0425 = A 550, WDS 17471+1742 = STF 2215 and WDS 18025+4414 = BU 1127 Aa-B. In addition, for three binaries - WDS 01532+1526 = BU 260, WDS 02563+7253 = STF 312 AB and WDS 05003+3924 = STT 92 AB - the orbital elements are calculated for the first time. In this paper the authors present not only the orbital elements, but the masses dynamical parallaxes, absolute magnitudes and ephemerides for the next five years, as well.

  2. Equational binary decision diagrams

    NARCIS (Netherlands)

    Groote, J.F.; Pol, J.C. van de

    2000-01-01

    We incorporate equations in binary decision diagrams (BDD). The resulting objects are called EQ-BDDs. A straightforward notion of ordered EQ-BDDs (EQ-OBDD) is defined, and it is proved that each EQ-BDD is logically equivalent to an EQ-OBDD. Moreover, on EQ-OBDDs satisfiability and tautology checkin

  3. Effect of Colloidal Interactions on the Rate of Interdroplet Heterogeneous Nucleation in Oil-in-Water Emulsions

    Science.gov (United States)

    McClements; Dungan

    1997-02-01

    Pulsed nuclear magnetic resonance was used to monitor the crystallization of supercooled liquid droplets in 30 wt% n-hexadecane oil-in-water emulsions at 6°C. Crystallization was induced in the liquid droplets when solid droplets of the same material were present. The rate of induced crystallization increased as the concentration of free non-ionic surfactant (polyoxyethylene sorbitan monolaurate) in the aqueous phase increased from 0 to 14 wt%. Differential scanning calorimetry measurements indicated that free surfactant had no effect on crystal nucleation of individual droplets. These results indicate that the surfactant enhances induced crystallization by altering colloidal interactions between droplets. Creaming measurements showed that flocculation was enhanced in emulsions when the free surfactant concentration was increased. We propose that the presence of free surfactant micelles increases the attraction between droplets because of an osmotic effect, and this attraction facilitates the ability of solid crystals from one droplet to induce crystallization in an adjacent liquid droplet.

  4. Colloid Thrusters, Physics, Fabrication and Performance

    Science.gov (United States)

    2005-11-17

    response, including the time for reviewing in. tata needed, and completing and reviewing this collection of information. Send comments regarding this...a discussion with colleagues during the 2nd Colloid Thruster/ Nano Electrojet Workshop (MIT, April 14- 15, 2005, Ref. [11]) an agreement was reached...23 Jul 2003. 11. Second Colloid Thruster/ Nano Electrojet Workshop, CD with a collection of presentations by attendees to this Workshop. MIT, April 14

  5. Colloidal Silver Not Approved for Treating Animals

    OpenAIRE

    Bagley, Clell

    1997-01-01

    FDA has received reports that products containing colloidal silver are being promoted for use in the treatment of mastitis and other serious disease conditions of dairy cattle, as well as for various conditions of companion animals. For example, FDA’s Center for Veterinary Medicine has received reports from the Agency's regional milk specialists and State inspectors that colloidal silver products have been found on some dairy farms. Also, recent articles in some farm newspapers and journals p...

  6. Black holes in binary stars

    NARCIS (Netherlands)

    Wijers, R.A.M.J.

    1996-01-01

    Introduction Distinguishing neutron stars and black holes Optical companions and dynamical masses X-ray signatures of the nature of a compact object Structure and evolution of black-hole binaries High-mass black-hole binaries Low-mass black-hole binaries Low-mass black holes Formation of black holes

  7. 'Weird' crystal structures of elements at high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Kolobyanina, Tat' yana N [L.F. Vereshchagin Institute of High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow region (Russian Federation)

    2002-12-31

    New crystal structures, in particular incommensurate composite crystals, discovered in the high-pressure phases of Group I, II, IV, and V elements are described, and their intermetallic and other binary structural analogs are discussed. (reviews of topical problems)

  8. Colloids generation from metallic uranium fuel

    Energy Technology Data Exchange (ETDEWEB)

    Metz, C.; Fortner, J.; Goldberg, M.; Shelton-Davis, C.

    2000-07-20

    The possibility of colloid generation from spent fuel in an unsaturated environment has significant implications for storage of these fuels in the proposed repository at Yucca Mountain. Because colloids can act as a transport medium for sparingly soluble radionuclides, it might be possible for colloid-associated radionuclides to migrate large distances underground and present a human health concern. This study examines the nature of colloidal materials produced during corrosion of metallic uranium fuel in simulated groundwater at elevated temperature in an unsaturated environment. Colloidal analyses of the leachates from these corrosion tests were performed using dynamic light scattering and transmission electron microscopy. Results from both techniques indicate a bimodal distribution of small discrete particles and aggregates of the small particles. The average diameters of the small, discrete colloids are {approximately}3--12 nm, and the large aggregates have average diameters of {approximately}100--200 nm. X-ray diffraction of the solids from these tests indicates a mineral composition of uranium oxide or uranium oxy-hydroxide.

  9. Colloids with high-definition surface structures.

    Science.gov (United States)

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-07-03

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of approximately 10(7) to 10(8) particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors.

  10. Complex coacervation between colloidal silica and polyacrylamide

    Energy Technology Data Exchange (ETDEWEB)

    Kawase, Kaoru; Sakami, Hiroshi; Hayakawa, Kiyoshi

    1989-03-01

    Complex coacervation introduced by gamma-ray induced polymerization of acrylamide in colloidal silica was studied. The complex coaservate was formed by polymerization of acrylamide dissolved in a colloidal silica and methanol mixture. Complex coacervation (two-phase separation of the mixture) was observed only when the concentration of methanol was between 33 and 41 percent by volume, and the concentration of colloidal silica did not affect it. Although two phase separation was not influenced by pH change, the content of polyacrylamide was bigger in the equilibrated solution in acidic regions. It was, however, bigger in the complex coacervate at neutral and in alkaline regions. The content of polyacrylamide was also calculated from the particle diameter of complex coacervate measured by small angle X-ray scattering, and the result was well coincided with the analytical result. The stability of the complex coacervate against the addition of salts was better than that of the untreated colloidal silica. The rate of electrophoretic transport of the complex coacervate was also lower than that of the colloidal silica. From these observation it was concluded that the hydrophobic colloidal silica particles were protected by the surrounding hydrophilic polyacrylamide. (author).

  11. Colloidal oatmeal: history, chemistry and clinical properties.

    Science.gov (United States)

    Kurtz, Ellen S; Wallo, Warren

    2007-02-01

    Oatmeal has been used for centuries as a soothing agent to relieve itch and irritation associated with various xerotic dermatoses. In 1945, a ready to use colloidal oatmeal, produced by finely grinding the oat and boiling it to extract the colloidal material, became available. Today, colloidal oatmeal is available in various dosage forms from powders for the bath to shampoos, shaving gels, and moisturizing creams. Currently, the use of colloidal oatmeal as a skin protectant is regulated by the U.S. Food and Drug Administration (FDA) according to the Over-The-Counter Final Monograph for Skin Protectant Drug Products issued in June 2003. Its preparation is also standardized by the United States Pharmacopeia. The many clinical properties of colloidal oatmeal derive from its chemical polymorphism. The high concentration in starches and beta-glucan is responsible for the protective and water-holding functions of oat. The presence of different types of phenols confers antioxidant and anti-inflammatory activity. Some of the oat phenols are also strong ultraviolet absorbers. The cleansing activity of oat is mostly due to saponins. Its many functional properties make colloidal oatmeal a cleanser, moisturizer, buffer, as well as a soothing and protective anti-inflammatory agent.

  12. Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

    Energy Technology Data Exchange (ETDEWEB)

    Wen, L.S.; Santschi, P.H.; Tang, D. [Texas A & M Univ., Galveston, TX (United States)

    1997-07-01

    It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority ( >50%) of the colloidal trace metals had been transferred into the particulate phase ({ge} 0.45{mu}m), except for {sup 65}Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe ({approximately}60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of {sup 59}Fe and {sup 110}Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of {sup 54}Mn, {sup 133}Ba, {sup 65}Zn, {sup 109}Cd, {sup 113}Sn, and {sup 60}Co increased while the LMW({le}1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying affinities for different trace metals. 39 refs., 8 figs., 3 tabs.

  13. Learning to assign binary weights to binary descriptor

    Science.gov (United States)

    Huang, Zhoudi; Wei, Zhenzhong; Zhang, Guangjun

    2016-10-01

    Constructing robust binary local feature descriptors are receiving increasing interest due to their binary nature, which can enable fast processing while requiring significantly less memory than their floating-point competitors. To bridge the performance gap between the binary and floating-point descriptors without increasing the computational cost of computing and matching, optimal binary weights are learning to assign to binary descriptor for considering each bit might contribute differently to the distinctiveness and robustness. Technically, a large-scale regularized optimization method is applied to learn float weights for each bit of the binary descriptor. Furthermore, binary approximation for the float weights is performed by utilizing an efficient alternatively greedy strategy, which can significantly improve the discriminative power while preserve fast matching advantage. Extensive experimental results on two challenging datasets (Brown dataset and Oxford dataset) demonstrate the effectiveness and efficiency of the proposed method.

  14. Control of colloids with gravity, temperature gradients, and electric fields

    CERN Document Server

    Sullivan, M; Harrison, C; Austin, R H; Megens, M; Hollingsworth, A; Russel, W B; Cheng Zhen; Mason, T; Chaikin, P M

    2003-01-01

    We have used a variety of different applied fields to control the density, growth, and structure of colloidal crystals. Gravity exerts a body force proportional to the buoyant mass and in equilibrium produces a height-dependent concentration profile. A similar body force can be obtained with electric fields on charged particles (electrophoresis), a temperature gradient on all particles, or an electric field gradient on uncharged particles (dielectrophoresis). The last is particularly interesting since its magnitude and sign can be changed by tuning the applied frequency. We study these effects in bulk (making 'dielectrophoretic bottles' or traps), to control concentration profiles during nucleation and growth and near surfaces. We also study control of non-spherical and optically anisotropic particles with the light field from laser tweezers.

  15. Optofluidic taming of a colloidal dimer with a silicon nanocavity

    Energy Technology Data Exchange (ETDEWEB)

    Pin, C.; Renaut, C. [Groupe d' Optique de Champ Proche - LRC CEA n°DSM-08-36, Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS n°6303- Université de Bourgogne, Dijon (France); University Grenoble Alpes, INAC-SP2M-SINAPS, F-38000 Grenoble, France and CEA, INAC-SP2M-SINAPS, F-38000 Grenoble (France); University Grenoble Alpes, CNRS, CEA-Leti Minatec, LTM, F-38054 Grenoble Cedex (France); Cluzel, B., E-mail: benoit.cluzel@u-bourgogne.fr; Fornel, F. de [Groupe d' Optique de Champ Proche - LRC CEA n°DSM-08-36, Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR CNRS n°6303- Université de Bourgogne, Dijon (France); Peyrade, D. [University Grenoble Alpes, CNRS, CEA-Leti Minatec, LTM, F-38054 Grenoble Cedex (France); Picard, E.; Hadji, E. [University Grenoble Alpes, INAC-SP2M-SINAPS, F-38000 Grenoble, France and CEA, INAC-SP2M-SINAPS, F-38000 Grenoble (France)

    2014-10-27

    We report here the optical trapping of a heterogeneous colloidal dimer above a photonic crystal nanocavity used as an on-chip optical tweezer. The trapped dimer consists of a cluster of two dielectric microbeads of different sizes linked by van der Waals forces. The smallest bead, 1 μm in diameter, is observed to be preferentially trapped by the nanotweezer, leaving the second bead untrapped. The rotational nature of the trapped dimer Brownian motion is first evidenced. Then, in the presence of a fluid flow, control of its orientation and rotation is achieved. The whole system is found to show high rotational degrees of freedom, thereby acting as an effective flow-sensitive microscopic optical ball joint.

  16. Colloid's influences on microalgae growth as a potential environmental factor

    Institute of Scientific and Technical Information of China (English)

    赵新淮; 张正斌; 刘莲生

    2003-01-01

    The role of colloid as "colloid pump" in the ocean is well known. The important influence of colloid in seawater on the growth of microalga was found in our 1999-2000 study. Colloid concentrates were obtained by employing a cross-flow filtration systen to ultrafilter seawater (which had been pre-filtrated by 0.45 μm acetate cellulose membrane) successively with different membranes. Ultrafiltration retentions (we called them colloid concentrates ) together with control sample ( seawater without colloid) were then inoculated with two species of microalgae and cultivated in selected conditions. Monitoring of microalgae growth during cultivation showed that all colloid concentrates had obvious influence on the growth of the microalgae studied. Addition of Fe(OH)3 colloid or organic colloid (protein or carbohydrate) to the control sample enhanced the microalgae's growth.

  17. Photonic crystal waveguides by direct writing of e-beam on self-assembled photonic crystals

    Indian Academy of Sciences (India)

    Sunita Kedia; R Vijaya

    2011-04-01

    Direct electron beam lithography technique is used for writing a variety of waveguide structures on thin films of polymethyl methacrylate (PMMA) and self-assembled three-dimensionally ordered photonic crystals made up of PMMA colloidal spheres. The waveguide structures fabricated on both these type of samples are characterized by scanning electron microscope and optical microscope images.

  18. 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.

  19. Colloidal Gelation-2 and Colloidal Disorder-Order Transition-2 Investigations Conducted on STS-95

    Science.gov (United States)

    Hoffmann, Monica T.

    2000-01-01

    The Colloidal Gelation-2 (CGEL 2) and Colloidal Disorder-Order Transition-2 (CDOT 2) investigations flew on Space Shuttle Discovery mission STS-95 (also known as the John Glenn Mission). These investigations were part of a series of colloid experiments designed to help scientists answer fundamental science questions and reduce the trial and error involved in developing new and better materials. Industries dealing with semiconductors, electro-optics, ceramics, and composites are just a few that may benefit from this knowledge. The goal of the CGEL 2 investigation was to study the fundamental properties of colloids to help scientists better understand their nature and make them more useful for technology. Colloids consist of very small (submicron) particles suspended in a fluid. They play a critical role in the technology of this country, finding uses in materials ranging from paints and coatings to drugs, cosmetics, food, and drink. Although these products are routinely produced and used, there are still many aspects of their behavior about which scientists know little. Understanding their structures may allow scientists to manipulate the physical properties of colloids (a process called "colloidal engineering") to produce new materials and products. Colloid research may even improve the processing of known products to enhance their desirable properties.

  20. Drying of thin colloidal films

    Science.gov (United States)

    Routh, Alexander F.

    2013-04-01

    When thin films of colloidal fluids are dried, a range of transitions are observed and the final film profile is found to depend on the processes that occur during the drying step. This article describes the drying process, initially concentrating on the various transitions. Particles are seen to initially consolidate at the edge of a drying droplet, the so-called coffee-ring effect. Flow is seen to be from the centre of the drop towards the edge and a front of close-packed particles passes horizontally across the film. Just behind the particle front the now solid film often displays cracks and finally the film is observed to de-wet. These various transitions are explained, with particular reference to the capillary pressure which forms in the solidified region of the film. The reasons for cracking in thin films is explored as well as various methods to minimize its effect. Methods to obtain stratified coatings through a single application are considered for a one-dimensional drying problem and this is then extended to two-dimensional films. Different evaporative models are described, including the physical reason for enhanced evaporation at the edge of droplets. The various scenarios when evaporation is found to be uniform across a drying film are then explained. Finally different experimental techniques for examining the drying step are mentioned and the article ends with suggested areas that warrant further study.

  1. 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.

  2. Color from hierarchy: Diverse optical properties of micron-sized spherical colloidal assemblies.

    Science.gov (United States)

    Vogel, Nicolas; Utech, Stefanie; England, Grant T; Shirman, Tanya; Phillips, Katherine R; Koay, Natalie; Burgess, Ian B; Kolle, Mathias; Weitz, David A; Aizenberg, Joanna

    2015-09-01

    Materials in nature are characterized by structural order over multiple length scales have evolved for maximum performance and multifunctionality, and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction, and absorption effects result in vivid colors. Mimicking this emergence of complex effects from simple building blocks is a key challenge for man-made materials. Here, we show that a simple confined self-assembly process leads to a complex hierarchical geometry that displays a variety of optical effects. Colloidal crystallization in an emulsion droplet creates micron-sized superstructures, termed photonic balls. The curvature imposed by the emulsion droplet leads to frustrated crystallization. We observe spherical colloidal crystals with ordered, crystalline layers and a disordered core. This geometry produces multiple optical effects. The ordered layers give rise to structural color from Bragg diffraction with limited angular dependence and unusual transmission due to the curved nature of the individual crystals. The disordered core contributes nonresonant scattering that induces a macroscopically whitish appearance, which we mitigate by incorporating absorbing gold nanoparticles that suppress scattering and macroscopically purify the color. With increasing size of the constituent colloidal particles, grating diffraction effects dominate, which result from order along the crystal's curved surface and induce a vivid polychromatic appearance. The control of multiple optical effects induced by the hierarchical morphology in photonic balls paves the way to use them as building blocks for complex optical assemblies--potentially as more efficient mimics of structural color as it occurs in nature.

  3. The Binary Garrote

    CERN Document Server

    Kappen, H J

    2011-01-01

    In this paper, I present a new model and solution method for sparse regression. The model introduces binary selector variables $s_i$ for the features $i$ in a way that is similar to Breiman's Garrote model. I refer to this method as the binary Garrote (BG). The posterior probability for $s_i$ is computed in the variational approximation. The BG is compared numerically with the Lasso method and with ridge regression. Numerical results on synthetic data show that the BG yields more accurate predictions and more accurately reconstructs the true model than the other methods. The naive implementation of the BG requires the inversion of a modified covariance matrix which scales cubic in the number of features. We indicate how for sparse problem the solution can be computed linear in the number of features.

  4. Binary Tetrahedral Flavor Symmetry

    CERN Document Server

    Eby, David A

    2013-01-01

    A study of the T' Model and its variants utilizing Binary Tetrahedral Flavor Symmetry. We begin with a description of the historical context and motivations for this theory, together with some conceptual background for added clarity, and an account of our theory's inception in previous works. Our model endeavors to bridge two categories of particles, leptons and quarks, a unification made possible by the inclusion of additional Higgs particles, shared between the two fermion sectors and creating a single coherent system. This is achieved through the use of the Binary Tetrahedral symmetry group and an investigation of the Tribimaximal symmetry evidenced by neutrinos. Our work details perturbations and extensions of this T' Model as we apply our framework to neutrino mixing, quark mixing, unification, and dark matter. Where possible, we evaluate model predictions against experimental results and find excellent matching with the atmospheric and reactor neutrino mixing angles, an accurate prediction of the Cabibb...

  5. Binary Love Relations

    CERN Document Server

    Yagi, Kent

    2015-01-01

    When in a tight binary, the mutual tidal deformations of neutron stars imprint onto observables, encoding information about their internal structure at supranuclear densities and gravity in the extreme-gravity regime. Gravitational wave observations of their late binary inspiral may serve as a tool to extract the individual tidal deformabilities, but this is made difficult by degeneracies between them in the gravitational wave model. We here resolve this problem by discovering approximately universal relations between dimensionless combinations of the individual tidal deformabilities. We show that these relations break degeneracies in the gravitational wave model, allowing for the accurate extraction of both deformabilities. Such measurements can be used to better differentiate between equation-of-state models, and improve tests of General Relativity and cosmology.

  6. Binary Love relations

    Science.gov (United States)

    Yagi, Kent; Yunes, Nicolás

    2016-07-01

    When in a tight binary, the mutual tidal deformations of neutron stars get imprinted onto observables, encoding information about their internal structure at supranuclear densities and gravity in the extreme-gravity regime. Gravitational wave (GW) observations of their late binary inspiral may serve as a tool to extract the individual tidal deformabilities, but this is made difficult by degeneracies between them in the GW model. We here resolve this problem by discovering approximately equation-of-state (EoS)-insensitive relations between dimensionless combinations of the individual tidal deformabilities. We show that these relations break degeneracies in the GW model, allowing for the accurate extraction of both deformabilities. Such measurements can be used to better differentiate between EoS models, and improve tests of general relativity and cosmology.

  7. Effect of many-body interactions on the bulk and interfacial phase behavior of a model colloid-polymer mixture.

    Science.gov (United States)

    Dijkstra, Marjolein; van Roij, René; Roth, Roland; Fortini, Andrea

    2006-04-01

    We study a model suspension of sterically stabilized colloidal particles and nonadsorbing ideal polymer coils, both in bulk and adsorbed against a planar hard wall. By integrating out the degrees of freedom of the polymer coils, we derive a formal expression for the effective one-component Hamiltonian of the colloids. We employ an efficient Monte Carlo simulation scheme for this mixture based on the exact effective colloid Hamiltonian; i.e., it incorporates all many-body interactions. The many-body character of the polymer-mediated effective interactions between the colloids yields bulk phase behavior and adsorption phenomena that differ substantially from those found for pairwise simple fluids. We determine the phase behavior for size ratios q=sigma(p)/sigma(c)=1, 0.6, and 0.1, where sigma(c) and sigma(p) denote the diameters of the colloids and polymer coils, respectively. For q=1 and 0.6, we find both a fluid-solid and a stable colloidal gas-liquid transition with an anomalously large bulk liquid regime caused by the many-body interactions. We compare the phase diagrams obtained from simulations with the results of the free-volume approach and with direct simulations of the true binary mixture. Although we did not simulate the polymer coils explicitly, we are able to obtain the three partial structure factors and radial distribution functions. We compare our results with those obtained from density functional theory and the Percus-Yevick approximation. We find good agreement between all results for the structure. We also study the mixture in contact with a single hard wall for q=1. Upon approach of the gas-liquid binodal, we find far from the triple point, three layering transitions in the partial wetting regime.

  8. Binary-Signal Recovery

    Science.gov (United States)

    Griebeler, Elmer L.

    2011-01-01

    Binary communication through long cables, opto-isolators, isolating transformers, or repeaters can become distorted in characteristic ways. The usual solution is to slow the communication rate, change to a different method, or improve the communication media. It would help if the characteristic distortions could be accommodated at the receiving end to ease the communication problem. The distortions come from loss of the high-frequency content, which adds slopes to the transitions from ones to zeroes and zeroes to ones. This weakens the definition of the ones and zeroes in the time domain. The other major distortion is the reduction of low frequency, which causes the voltage that defines the ones or zeroes to drift out of recognizable range. This development describes a method for recovering a binary data stream from a signal that has been subjected to a loss of both higher-frequency content and low-frequency content that is essential to define the difference between ones and zeroes. The method makes use of the frequency structure of the waveform created by the data stream, and then enhances the characteristics related to the data to reconstruct the binary switching pattern. A major issue is simplicity. The approach taken here is to take the first derivative of the signal and then feed it to a hysteresis switch. This is equivalent in practice to using a non-resonant band pass filter feeding a Schmitt trigger. Obviously, the derivative signal needs to be offset to halfway between the thresholds of the hysteresis switch, and amplified so that the derivatives reliably exceed the thresholds. A transition from a zero to a one is the most substantial, fastest plus movement of voltage, and therefore will create the largest plus first derivative pulse. Since the quiet state of the derivative is sitting between the hysteresis thresholds, the plus pulse exceeds the plus threshold, switching the hysteresis switch plus, which re-establishes the data zero to one transition

  9. Colloids with continuously tunable surface charge.

    Science.gov (United States)

    van Ravensteijn, Bas G P; Kegel, Willem K

    2014-09-09

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

  10. 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.

  11. Massive Black Hole Binary Evolution

    Directory of Open Access Journals (Sweden)

    Merritt David

    2005-11-01

    Full Text Available Coalescence of binary supermassive black holes (SBHs would constitute the strongest sources of gravitational waves to be observed by LISA. While the formation of binary SBHs during galaxy mergers is almost inevitable, coalescence requires that the separation between binary components first drop by a few orders of magnitude, due presumably to interaction of the binary with stars and gas in a galactic nucleus. This article reviews the observational evidence for binary SBHs and discusses how they would evolve. No completely convincing case of a bound, binary SBH has yet been found, although a handful of systems (e.g. interacting galaxies; remnants of galaxy mergers are now believed to contain two SBHs at projected separations of <~ 1kpc. N-body studies of binary evolution in gas-free galaxies have reached large enough particle numbers to reproduce the slow, “diffusive” refilling of the binary’s loss cone that is believed to characterize binary evolution in real galactic nuclei. While some of the results of these simulations - e.g. the binary hardening rate and eccentricity evolution - are strongly N-dependent, others - e.g. the “damage” inflicted by the binary on the nucleus - are not. Luminous early-type galaxies often exhibit depleted cores with masses of ~ 1-2 times the mass of their nuclear SBHs, consistent with the predictions of the binary model. Studies of the interaction of massive binaries with gas are still in their infancy, although much progress is expected in the near future. Binary coalescence has a large influence on the spins of SBHs, even for mass ratios as extreme as 10:1, and evidence of spin-flips may have been observed.

  12. Visual binary stars: data to investigate formation of binaries

    Science.gov (United States)

    Kovaleva,, D.; Malkov,, O.; Yungelson, L.; Chulkov, D.

    Statistics of orbital parameters of binary stars as well as statistics of their physical characteristics bear traces of star formation history. However, statistical investigations of binaries are complicated by incomplete or missing observational data and by a number of observational selection effects. Visual binaries are the most common type of observed binary stars, with the number of pairs exceeding 130 000. The most complete list of presently known visual binary stars was compiled by cross-matching objects and combining data of the three largest catalogues of visual binaries. This list was supplemented by the data on parallaxes, multicolor photometry, and spectral characteristics taken from other catalogues. This allowed us to compensate partly for the lack of observational data for these objects. The combined data allowed us to check the validity of observational values and to investigate statistics of the orbital and physical parameters of visual binaries. Corrections for incompleteness of observational data are discussed. The datasets obtained, together with modern distributions of binary parameters, will be used to reconstruct the initial distributions and parameters of the function of star formation for binary systems.

  13. Inorganic passivation and doping control in colloidal quantum dot photovoltaics

    KAUST Repository

    Hoogland, Sjoerd H.

    2012-01-01

    We discuss strategies to reduce midgap trap state densities in colloidal quantum dot films and requirements to control doping type and magnitude. We demonstrate that these improvements result in colloidal quantum dot solar cells with certified 7.0% efficiency.

  14. Neptunium Colloidal Behaviors in Present of Humic Acids

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    <正>The colloidal-borne facilitated transport of actinides is an important part of radionuclide migration investigation in HLW geological disposal. In the present studies, Np colloidal behaviors in present of

  15. Self-consistent generalized Langevin equation for colloidal mixtures.

    Science.gov (United States)

    Chávez-Rojo, Marco Antonio; Medina-Noyola, Magdaleno

    2005-09-01

    A self-consistent theory of collective and tracer diffusion in colloidal mixtures is presented. This theory is based on exact results for the partial intermediate scattering functions derived within the framework of the generalized Langevin equation formalism, plus a number of conceptually simple and sensible approximations. The first of these consists of a Vineyard-like approximation between collective and tracer diffusion, which writes the collective dynamics in terms of the memory function related to tracer diffusion. The second consists of interpolating this only unknown memory function between its two exact limits at small and large wave vectors; for this, a phenomenologically determined, but not arbitrary, interpolating function is introduced: a Lorentzian with its inflection point located at the first minimum of the partial static structure factor. The small wave-vector exact limit involves a time-dependent friction function, for which we take a general approximate result, previously derived within the generalized Langevin equation formalism. This general result expresses the time-dependent friction function in terms of the partial intermediate scattering functions, thus closing the system of equations into a fully self-consistent scheme. This extends to mixtures a recently proposed self-consistent theory developed for monodisperse suspensions [Yeomans-Reyna and Medina-Noyola, Phys. Rev. E 64, 066114 (2001)]. As an illustration of its quantitative accuracy, its application to a simple model of a binary dispersion in the absence of hydrodynamic interactions is reported.

  16. 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.

  17. Springer Handbook of Crystal Growth

    CERN Document Server

    Dhanaraj, Govindhan; Prasad, Vishwanath; Dudley, Michael

    2010-01-01

    Over the years, many successful attempts have been made to describe the art and science of crystal growth. Most modern advances in semiconductor and optical devices would not have been possible without the development of many elemental, binary, ternary, and other compound crystals of varying properties and large sizes. The objective of the Springer Handbook of Crystal Growth is to present state-of-the-art knowledge of both bulk and thin-film crystal growth. The goal is to make readers understand the basics of the commonly employed growth processes, materials produced, and defects generated. Almost 100 leading scientists, researchers, and engineers from 22 different countries from academia and industry have been selected to write chapters on the topics of their expertise. They have written 52 chapters on the fundamentals of bulk crystal growth from the melt, solution, and vapor, epitaxial growth, modeling of growth processes and defects, techniques of defect characterization as well as some contemporary specia...

  18. Shape-shifting colloids via stimulated dewetting

    Science.gov (United States)

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-07-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly.

  19. TOPICAL REVIEW: Biological applications of colloidal nanocrystals

    Science.gov (United States)

    Parak, Wolfgang J.; Gerion, Daniele; Pellegrino, Teresa; Zanchet, Daniela; Micheel, Christine; Williams, Shara C.; Boudreau, Rosanne; LeGros, Mark A.; Larabell, Carolyn A.; Alivisatos, A. Paul

    2003-07-01

    Due to their interesting properties, research on colloidal nanocrystals has moved in the last few years from fundamental research to first applications in materials science and life sciences. In this review some recent biological applications of colloidal nanocrystals are discussed, without going into biological or chemical details. First, the properties of colloidal nanocrystals and how they can be synthesized are described. Second, the conjugation of nanocrystals with biological molecules is discussed. And third, three different biological applications are introduced: (i) the arrangement of nanocrystal-oligonucleotide conjugates using molecular scaffolds such as single-stranded DNA, (ii) the use of nanocrystal-protein conjugates as fluorescent probes for cellular imaging, and (iii) a motility assay based on the uptake of nanocrystals by living cells.

  20. Charge-transfer processes in semiconductor colloids

    Science.gov (United States)

    Kamat, Prashant V.; Gopidas, K. R.

    1990-04-01

    A picosecond transient absorption spectroscopy technique has been employed to probe the charge transfer processes in Ti02 semiconductor colloids. The trapping of electrons at the TiO surface (Ti4+ sitesY was characterized from the appearance of a broad absorption in the region of 550-750 nm following the 355-nm laser pulse excitation of Ti02 colloids. The lifetime of these trapped charge carriers increased upon incorporation of a hole scavenger in the colloidal semiconductor system. The mechanistic and kinetic details of the charge injection from excited CdS into a large bandgap semiconductor such as AgI and Ti02 have also been inves-' t i ga ted.

  1. Doped Colloidal ZnO Nanocrystals

    Directory of Open Access Journals (Sweden)

    Yizheng Jin

    2012-01-01

    Full Text Available Colloidal ZnO nanocrystals are promising for a wide range of applications due to the combination of unique multifunctional nature and remarkable solution processability. Doping is an effective approach of enhancing the properties of colloidal ZnO nanocrystals in well-controlled manners. In this paper, we analyzed two synthetic strategies for the doped colloidal ZnO nanocrystals, emphasizing our understanding on the critical factors associated with the high temperature and nonaqueous approach. Latest advances of three topics, bandgap engineering, n-type doping, and dilute magnetic semiconductors related to doped ZnO nanocrystals were discussed to reveal the effects of dopants on the properties of the nanocrystalline materials.

  2. Dynamic Assembly of Magnetic Colloidal Vortices

    Energy Technology Data Exchange (ETDEWEB)

    Mohorič, Tomaž; Kokot, Gašper; Osterman, Natan; Snezhko, Alexey; Vilfan, Andrej; Babič, Dušan; Dobnikar, Jure

    2016-04-29

    Magnetic colloids in external time-dependent fields are subject to complex induced many-body interactions governing their self-assembly into a variety of equilibrium and out-of-equilibrium structures such as chains, networks, suspended membranes, and colloidal foams. Here, we report experiments, simulations, and theory probing the dynamic assembly of superparamagnetic colloids in precessing external magnetic fields. Within a range of field frequencies, we observe dynamic large-scale structures such as ordered phases composed of precessing chains, ribbons, and rotating fluidic vortices. We show that the structure formation is inherently coupled to the buildup of torque, which originates from internal relaxation of induced dipoles and from transient correlations among the particles as a result of short-lived chain formation. We discuss in detail the physical properties of the vortex phase and demonstrate its potential in particle-coating applications.

  3. Enhanced photoredox chemistry in quantized semiconductor colloids

    Energy Technology Data Exchange (ETDEWEB)

    Nedeljkovic, J.M.; Nenadovic, M.T.; Micic, O.I.; Nozik, A.J.

    1986-01-02

    Optical effects due to size quantization have been observed for HgSe, PbSe, and CdSe colloids in water and acetonitrile with particle diameters of 20-100 A. For diameters less than 50 A, the optical absorption edge of HgSe and PbSe is blue shifted by several volts. The results are consistent with perturbation of the semiconductor band structure due to carrier confinement in very small particles resulting in an increase in the effective band gap. The redox potential of photogenerated carriers is greatly enhanced in such quantized semiconductor particles; reduction reactions that cannot occur in bulk materials can occur in sufficiently small particles. This has been demonstrated with H/sub 2/ evolution in 50-A PbSe and HgSe colloids and CO/sub 2/ reduction in 50-A CdSe colloids. 13 references, 3 figures.

  4. Plasmonic films based on colloidal lithography.

    Science.gov (United States)

    Ai, Bin; Yu, Ye; Möhwald, Helmuth; Zhang, Gang; Yang, Bai

    2014-04-01

    This paper reviews recent advances in the field of plasmonic films fabricated by colloidal lithography. Compared with conventional lithography techniques such as electron beam lithography and focused ion beam lithography, the unconventional colloidal lithography technique with advantages of low-cost and high-throughput has made the fabrication process more efficient, and moreover brought out novel films that show remarkable surface plasmon features. These plasmonic films include those with nanohole arrays, nanovoid arrays and nanoshell arrays with precisely controlled shapes, sizes, and spacing. Based on these novel nanostructures, optical and sensing performances can be greatly enhanced. The introduction of colloidal lithography provides not only efficient fabrication processes but also plasmonic films with unique nanostructures, which are difficult to be fabricated by conventional lithography techniques.

  5. Manipulating semiconductor colloidal stability through doping.

    Science.gov (United States)

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

    2014-10-10

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

  6. Microstructure, local dynamics, and flow behavior of colloidal suspensions with weak attractive interactions

    Science.gov (United States)

    Weis, Clara; Oelschlaeger, Claude; Dijkstra, Dick; Ranft, Meik; Willenbacher, Norbert

    2016-09-01

    We present a comprehensive micro- and macrorheological study of the effect of weak depletion attraction (Ψdep ≈ 1-10 kBT) on dense colloidal suspensions stabilized by short-range repulsive interactions. We used aqueous polymer dispersions as model system and demonstrated the unique capabilities of multiple particle tracking (MPT) to disclose structural changes in such technically important systems exhibiting many characteristic features of hard sphere systems. Below the hard sphere freezing point ϕc, viscosity increases monotonically with increasing Ψdep due to the transition from a fluid to a fluid/crystalline and finally to a gel state. Above ϕc, increasing attraction strength first results in a viscosity reduction corresponding to the formation of large, permeable crystals and then in a viscosity increase when a network of dense, small crystals forms. The fraction of the fluid and crystal phase, particle concentration in each phase as well as the modulus of the micro-crystals are obtained, the latter decreases with Ψdep. Above the colloidal glass transition strong heterogeneities and different local particle mobility in the repulsive and attractive arrested states are found. Particles are trapped in the cage of neighboring particles rather than in an attractive potential well. The intermediate ergodic state exhibits uniform tracer diffusivity.

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

    Science.gov (United States)

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

    2017-03-01

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

  8. Colloidal interactions in two-dimensional nematic emulsions

    Indian Academy of Sciences (India)

    N M Silvestre; P Patrício; M M Telo Da Gama

    2005-06-01

    We review theoretical and experimental work on colloidal interactions in two-dimensional (2D) nematic emulsions. We pay particular attention to the effects of (i) the nematic elastic constants, (ii) the size of the colloids, and (iii) the boundary conditions at the particles and the container. We consider the interactions between colloids and fluid (deformable) interfaces and the shape of fluid colloids in smectic-C films.

  9. Colloidal dispersions in external fields: from equilibrium to non-equilibrium

    Science.gov (United States)

    Lowen, Hartmut

    2010-03-01

    Dispersions of colloidal particles are excellent model systems of classical statistical mechanics in order to understand the principles of self-organization processes. Using an external field (e.g. electric or magnetic field) the effective interaction between the colloidal particles can be tailored and the system can be brought into non-equilibrium in a controlled way. Glass formation after an ultrafast quench in a two-dimensional superparamagnetic binary colloidal mixture [1,2] will be discussed as well as lane [3,4,5,6,7] and band [8] formation in mixtures of charged suspensions and dusty plasmas driven by an electric field. [4pt] References:[0pt] [1] L. Assoud, F. Ebert, P. Keim, R. Messina, G. Maret, H. Lowen, Phys. Rev. Letters 102, 238301 (2009). [0pt] [2] L. Assoud, F. Ebert, P. Keim, R. Messina, G. Maret, H. Lowen, J. Phys.: Condensed Matter 21, 464114 (2009). [0pt] [3] J. Dzubiella, G. P. Hoffmann, H. Lowen, Phys. Rev. E 65, 021402 (1-8) (2002). [0pt] [4] M. E. Leunissen, C. G. Christova, A. P. Hynninen, C. P. Royall, A. I. Campbell, A. Imhof, M. Dijkstra, R. van Roij, A. van Blaaderen, Nature 437, 235 (2005). [0pt] [5] M. Rex, H. Lowen, Phys. Rev. E 75, 051402 (2007). [0pt] [6] M. Rex, C. P. Royall, A. van Blaaderen, H. Lowen, Lane formation in driven colloidal mixtures: is it continuous or discontinuous?, http://arxiv.org/abs/0812.0908 [0pt] [7] K. R. Sutterlin, A. Wysocki, A. V. Ivlev, C. Rath, H. M. Thomas, M. Rubin-Zuzic, W. J. Goedheer, V. E. Fortov, A. M. Lipaev, V. I. Molotkov, O. F. Petrov, G. E. Morfill, H. Lowen, Phys. Rev. Letters 102, 085003 (2009). [0pt] [8] A. Wysocki, H. Lowen, Phys. Rev. E 79, 041408 (2009).

  10. Oxyhydroxy Silicate Colloids: A New Type of Waterborne Actinide(IV) Colloids

    OpenAIRE

    Zänker, Harald; Weiss, Stephan; Hennig, Christoph; Brendler, Vinzenz; Ikeda‐Ohno, Atsushi

    2016-01-01

    Abstract At the near‐neutral and reducing aquatic conditions expected in undisturbed ore deposits or in closed nuclear waste repositories, the actinides Th, U, Np, and Pu are primarily tetravalent. These tetravalent actinides (AnIV) are sparingly soluble in aquatic systems and, hence, are often assumed to be immobile. However, AnIV could become mobile if they occur as colloids. This review focuses on a new type of AnIV colloids, oxyhydroxy silicate colloids. We herein discuss the chemical cha...

  11. Maximizing the Optical Band Gap in 2D Photonic Crystals

    DEFF Research Database (Denmark)

    Hougaard, Kristian G.; Sigmund, Ole

    Topology optimization is used to find the 2D photonic crystal designs with the largest relative photonic band gaps. Starting points for the topology optimization are found with an exhaustive binary search on a low resolution grid.......Topology optimization is used to find the 2D photonic crystal designs with the largest relative photonic band gaps. Starting points for the topology optimization are found with an exhaustive binary search on a low resolution grid....

  12. Dynamics of colloidal particles in ice

    KAUST Repository

    Spannuth, Melissa

    2011-01-01

    We use x-ray photon correlation spectroscopy (XPCS) to probe the dynamics of colloidal particles in polycrystalline ice. During freezing, the dendritic ice morphology and rejection of particles from the ice created regions of high particle density, where some of the colloids were forced into contact and formed disordered aggregates. The particles in these high density regions underwent ballistic motion, with a characteristic velocity that increased with temperature. This ballistic motion is coupled with both stretched and compressed exponential decays of the intensity autocorrelation function. We suggest that this behavior could result from ice grain boundary migration. © 2011 American Institute of Physics.

  13. Self-assembly of colloidal surfactants

    Science.gov (United States)

    Kegel, Willem

    2012-02-01

    We developed colloidal dumbbells with a rough and a smooth part, based on a method reported in Ref. [1]. Specific attraction between the smooth parts occurs upon addition of non-adsorbing polymers of appropriate size. We present the first results in terms of the assemblies that emerge in these systems. [4pt] [1] D.J. Kraft, W.S. Vlug, C.M. van Kats, A. van Blaaderen, A. Imhof and W.K. Kegel, Self-assembly of colloids with liquid protrusions, J. Am. Chem. Soc. 131, 1182, (2009)

  14. Shape recognition of microbial cells by colloidal cell imprints

    NARCIS (Netherlands)

    Borovicka, J.; Stoyanov, S.D.; Paunov, V.N.

    2013-01-01

    We have engineered a class of colloids which can recognize the shape and size of targeted microbial cells and selectively bind to their surfaces. These imprinted colloid particles, which we called "colloid antibodies", were fabricated by partial fragmentation of silica shells obtained by templating

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

    NARCIS (Netherlands)

    de Folter, J.W.J.

    2013-01-01

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

  16. 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

  17. Rotational mixing in close binaries

    CERN Document Server

    de Mink, S E; Langer, N; Yoon, S -Ch; Brott, I; Glebbeek, E; Verkoulen, M; Pols, O R

    2008-01-01

    Rotational mixing is a very important but uncertain process in the evolution of massive stars. We propose to use close binaries to test its efficiency. Based on rotating single stellar models we predict nitrogen surface enhancements for tidally locked binaries. Furthermore we demonstrate the possibility of a new evolutionary scenario for very massive (M > 40 solar mass) close (P < 3 days) binaries: Case M, in which mixing is so efficient that the stars evolve quasi-chemically homogeneously, stay compact and avoid any Roche-lobe overflow, leading to very close (double) WR binaries.

  18. Evolution of Close Binary Systems

    Energy Technology Data Exchange (ETDEWEB)

    Yakut, K; Eggleton, P

    2005-01-24

    We collected data on the masses, radii, etc. of three classes of close binary stars: low-temperature contact binaries (LTCBs), near-contact binaries (NCBs), and detached close binaries (DCBs). They restrict themselves to systems where (1) both components are, at least arguably, near the Main Sequence, (2) the periods are less than a day, and (3) there is both spectroscopic and photometric analysis leading to reasonably reliable data. They discuss the possible evolutionary connections between these three classes, emphasizing the roles played by mass loss and angular momentum loss in rapidly-rotating cool stars.

  19. Chaos in Binary Category Computation

    CERN Document Server

    Gonçalves, Carlos Pedro

    2010-01-01

    Category computation theory deals with a web-based systemic processing that underlies the morphic webs, which constitute the basis of categorial logical calculus. It is proven that, for these structures, algorithmically incompressible binary patterns can be morphically compressed, with respect to the local connectivities, in a binary morphic program. From the local connectivites, there emerges a global morphic connection that can be characterized by a low length binary string, leading to the identification of chaotic categorial dynamics, underlying the algorithmically random pattern. The work focuses on infinite binary chains of C2, which is a category that implements an X-OR-based categorial logical calculus.

  20. Complex plasmas and colloidal dispersions particle-resolved studies of classical liquids and solids

    CERN Document Server

    Ivlev, Alexei; Morfill, Gregor; Royall, C. Patrick

    2012-01-01

    Complex plasmas and colloidal dispersions represent different states of soft matter. They are complementary in many ways, with the most important being that complex plasmas are virtually undamped at the particle timescales, whereas colloidal dispersions are overdamped and therefore can be brought into equilibrium in a very controlled manner. Otherwise, both fields have similar advantages: fully resolved 3D particle trajectories can easily be visualized, the pair interactions are tunable, and particles can be manipulated individually or collectively. These unique properties allow us to investigate generic processes occurring in liquids or solids at the most fundamental individual particle level. The principal research topics to be addressed in the book include: particle dynamics in liquids, with the emphasis on mesoscopic processes in the supercooled (glassy) state, e.g. dynamical heterogeneity, phase transitions in solids, with particular attention to the evolutionary paths of crystal structure development an...

  1. Detection of phonon and phason modes in intrinsic colloidal quasicrystals by reconstructing their structure in hyperspace

    Science.gov (United States)

    Hielscher, J.; Martinsons, M.; Schmiedeberg, M.; Kapfer, S. C.

    2017-03-01

    Phasons are additional degrees of freedom which occur in quasicrystals alongside the phonons known from conventional periodic crystals. The rearrangements of particles that are associated with a phason mode are hard to interpret in physical space. We reconstruct the quasicrystal structure by an embedding into extended higher-dimensional space, where phasons correspond to displacements perpendicular to the physical space. In dislocation-free decagonal colloidal quasicrystals annealed with Brownian dynamics simulations, we identify thermal phonon and phason modes. Finite phononic strain is pinned by phasonic excitations even after cooling down to zero temperature. For the phasonic displacements underlying the flip pattern, the reconstruction method gives an approximation within the limits of a multi-mode harmonic ansatz, and points to fundamental limitations of a harmonic picture for phasonic excitations in intrinsic colloidal quasicrystals.

  2. Low autocorrelation binary sequences

    Science.gov (United States)

    Packebusch, Tom; Mertens, Stephan

    2016-04-01

    Binary sequences with minimal autocorrelations have applications in communication engineering, mathematics and computer science. In statistical physics they appear as groundstates of the Bernasconi model. Finding these sequences is a notoriously hard problem, that so far can be solved only by exhaustive search. We review recent algorithms and present a new algorithm that finds optimal sequences of length N in time O(N {1.73}N). We computed all optimal sequences for N≤slant 66 and all optimal skewsymmetric sequences for N≤slant 119.

  3. Microlensing modulation by binaries

    CERN Document Server

    Dubath, F; Durrer, R; Dubath, Florian; Gasparini, Maria Alice; Durrer, Ruth

    2006-01-01

    We compute the effect of the lens quadrupole on microlensing. The time dependence of the quadrupole can lead to specific modulations of the amplification signal. We study especially binary system lenses in our galaxy. The modulation is observable if the rotation period of the system is smaller than the time over which the amplification is significant and if the impact parameter of the passing light ray is sufficiently close to the Einstein radius so that the amplification is very large. Observations of this modulation can reveal important information on the quadrupole and thus on the gravitational radiation emitted by the lens.

  4. Perspective: The Asakura Oosawa model: A colloid prototype for bulk and interfacial phase behavior

    Energy Technology Data Exchange (ETDEWEB)

    Binder, Kurt; Virnau, Peter [Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudinger Weg 9, 55128 Mainz (Germany); Statt, Antonia [Graduate School of Excellence Material Science in Mainz, Staudinger Weg 9, 55128 Mainz (Germany)

    2014-10-14

    In many colloidal suspensions, the micrometer-sized particles behave like hard spheres, but when non-adsorbing polymers are added to the solution a depletion attraction (of entropic origin) is created. Since 60 years the Asakura-Oosawa model, which simply describes the polymers as ideal soft spheres, is an archetypical description for the statistical thermodynamics of such systems, accounting for many features of real colloid-polymer mixtures very well. While the fugacity of the polymers (which controls their concentration in the solution) plays a role like inverse temperature, the size ratio of polymer versus colloid radii acts as a control parameter to modify the phase diagram: when this ratio is large enough, a vapor-liquid like phase separation occurs at low enough colloid packing fractions, up to a triple point where a liquid-solid two-phase coexistence region takes over. For smaller size ratios, the critical point of the phase separation and the triple point merge, resulting in a single two-phase coexistence region between fluid and crystalline phases (of “inverted swan neck”-topology, with possibly a hidden metastable phase separation). Furthermore, liquid-crystalline ordering may be found if colloidal particles of non-spherical shape (e.g., rod like) are considered. Also interactions of the particles with solid surfaces should be tunable (e.g., walls coated by polymer brushes), and interfacial phenomena are particularly interesting experimentally, since fluctuations can be studied in the microscope on all length scales, down to the particle level. Due to its simplicity this model has become a workhorse for both analytical theory and computer simulation. Recently, generalizations addressing dynamic phenomena (phase separation, crystal nucleation, etc.) have become the focus of studies.

  5. Crystals in crystals

    DEFF Research Database (Denmark)

    Christensen, Claus H.; Schmidt, I.; Carlsson, A.;

    2005-01-01

    A major factor governing the performance of catalytically active particles supported on a zeolite carrier is the degree of dispersion. It is shown that the introduction of noncrystallographic mesopores into zeolite single crystals (silicalite-1, ZSM-5) may increase the degree of particle dispersion...... of the zeolite particles, particularly after thermal treatment. When using mesoporous zeolites, the particles were evenly distributed throughout the mesopore system of the zeolitic support, even after calcination, leading to nanocrystals within mesoporous zeolite single crystals....

  6. Spontaneous emission enhancement of colloidal CdSe nanoplatelets

    Science.gov (United States)

    Yang, Zhili; Pelton, Matthew; Waks, Edo

    Colloidal CdS /CdSe/CdS nanoplatelets synthesized recently are high efficient nano-emitters and gain media for nanoscale lasers and other nonlinear optical devices. They are characterized as quantum well structure due to energy gap difference between core CdSe and shell CdS, of which the luminescent wavelength could be tuned precisely by their thickness of growth. However, the influence of environment on the material's optical properties and further enhancement of the emission to implement nanoscale systems remains to be investigated. Here we demonstrate spontaneous emission rate enhancement of these CdSe nanoplatelets coupled to a photonic crystal cavity. We show clearly the photoluminescent spectrum modification of the nanoplatelets emission and an averaged Purcell enhancement factor of 3.1 is achieved when they are coupled to carefully-designed nanobeam photonic crystal cavities compared to the ones on unpatterned surface in our experiment of lifetime measurement. Also the phenomenon of cavity quality factor increasing is observed when increasing intensity of pumping, which attributes to saturable absorption of the nanoplatelets. Our success in enhancement of emission from these nanoplatelets here paves the road to realize actual nanoscale integrated systems such as ultra-low threshold micro-cavity lasers.

  7. Influence of biofilms on colloid transport: investigations with laponite as a model colloid

    Energy Technology Data Exchange (ETDEWEB)

    Leon-Morales, C.F.; Flemming, H.C.; Leis, A. [Duisburg Univ. (Germany). Inst. for Interface Biotechnology

    2003-07-01

    The synthetic clay mineral laponite RD was used as a model compound to investigate colloid transport in the presence of bacterial biofilms. A complex but pronounced delay in the transport of laponite was observed in colonised porous media, clearly demonstrating the influence of attached bacterial biomass on colloid transport. The transport of laponite under conditions which promoted laponite aggregation was associated with release of attached bacteria; this effect was shown to be independent of ionic strength, indicating that the colloids caused detachment of bacteria. Two major mechanisms are proposed to account for the different colloid transport patterns obtained in the presence or absence of biomass: (1) hydrodynamic effects due to aggregation of laponite and subsequent blockage of a proportion of the flow channels, and (2) sorption of laponite by bacterial biomass. (orig.)

  8. Dependence of crystallization of Brownian particles by sedimentation on the force direction

    Science.gov (United States)

    Sato, Masahide; Yusuf Hakim Widianto, Muhammad; Kanatsu, Youhei

    2015-11-01

    The formation of a large close-packed colloidal crystal with the fcc structure was observed during the sedimentation of colloidal particles in an inverted pyramidal pit [S. Matsuo et al., Appl. Phys. Lett. 82, 4285 (2003)]. Carrying out Brownian dynamics simulations, we confirmed that large grains with the fcc structure are formed when the apex angle of the inverted pyramidal container is suitable and the force direction is parallel to the the center axis [Y. Kanatsu and M. Sato, J. Phys. Soc. Jpn. 84, 044601 (2015)]. To form a high-quality colloidal crystal without defects, it is important to investigate in detail how the quality of a colloidal crystal is affected by the force direction and container shape. In this paper, we focus on the effect of the force direction on crystal quality and investigate how the ratio of the number of the hcp structured particles, Nhcp, to that of fcc structured particles, Nfcc, is affected by the force direction. In our simulation, the ratio of Nfcc to Nhcp is hardly changed when the force direction deviates from the central axis: Nfcc is much larger than Nhcp irrespective of the force direction. Thus, our results show that the crystal structure is insensitive to the force direction in forming a colloidal crystal by sedimentation in an inverted pyramidal container.

  9. Colloidal models. A bit of history

    NARCIS (Netherlands)

    Lyklema, J.

    2015-01-01

    This paper offers an anthology on developments in colloid and interface science emphasizing themes that may be of direct or indirect interest to Interfaces Against Pollution. Topics include the determination of Avogadro’s number, development in the insight into driving forces for double layer format

  10. Random packing of colloids and granular matter

    NARCIS (Netherlands)

    Wouterse, A.

    2008-01-01

    This thesis deals with the random packing of colloids and granular matter. A random packing is a stable disordered collection of touching particles, without long-range positional and orientational order. Experimental random packings of particles with the same shape but made of different materials sh

  11. Transformative Colloidal Nanomaterials for Mid- Infrared Devices

    Science.gov (United States)

    2015-06-11

    446 (2005) [2] Hillhouse, H.W., Beard, M.C., “Solar cells from colloidal nanocrystals: Fundamentals, materials, devices, and economics ,” Curr. Op...I., Fischer , A., Hoogland, S., Clifford, J., Klem, E., Levina, L., Sargent, EH., “Ultrasensitive solution-cast quantum dot photodetectors

  12. Cell shape recognition by colloidal cell imprints

    NARCIS (Netherlands)

    Borovička, Josef; Stoyanov, S.D.; Paunov, V.N.

    2015-01-01

    The results presented in this study are aimed at the theoretical estimate of the interactions between a spherical microbial cell and the colloidal cell imprints in terms of the Derjaguin, Landau, Vervey, and Overbeek (DLVO) surface forces. We adapted the Derjaguin approximation to take into accou

  13. Designing Zirconium Coated Polystyrene Colloids and Application

    Directory of Open Access Journals (Sweden)

    Diana Chira

    2009-01-01

    Full Text Available A simple technique has been developed to prepare core colloids that are modified using zirconium oxychloride, based on heating a solution of core colloid composites, consisting of poly (ethylenimine (PEI and zirconium oxychloride. The interaction of zirconium oxychloride with the polystyrene (PS core colloids has been investigated using Fourier transform-infrared spectroscopy (FT-IR, energy dispersive X-ray spectroscopy (EDX, and scanning electron microscopy (SEM data. FT-IR studies confirm the occurrence of amine groups present in PEI which are oxidized to carboxyl groups after the reaction. The EDX data and the SEM images confirm the presence of zirconium particles immobilized on the polystyrene surfaces. Demeton, a highly toxic nerve agent, was used due to its ability to easily bind through its organophosphate group illustrating a practical application of the PS-PEI-Zr particles. Attenuated Total Reflection (ATR Spectroscopy was used to assess the interactions between the toxic nerve agent demeton-S and the PS-PEI-Zr particles. The results show that the presented technique for coating polystyrene core colloids with zirconium was successfully accomplished, and the newly formed particles easily bond with demeton agents through the P=O functional group.

  14. 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.

  15. Repeptization and the theory of electrocratic colloids

    NARCIS (Netherlands)

    Frens, G.; Overbeek, J.Th.G.

    1972-01-01

    The coagulation and the repeptization of electrocratic colloids can be treated in one theory provided that the appropriate boundary conditions are chosen. From this version of the DLVO theory it follows that for each sol there exists a critical value Z∞c of the double layer parameter Z∞, Z∞ = zeδ/kT

  16. Phase behavior of colloidal silica rods

    NARCIS (Netherlands)

    Kuijk, A.; Byelov, D.; Petukhov, A.V.; van Blaaderen, A.; Imhof, A.

    2012-01-01

    Recently, a novel colloidal hard-rod-like model system was developed which consists of silica rods [Kuijk et al., JACS, 2011, 133, 2346]. Here, we present a study of the phase behavior of these rods, for aspect ratios ranging from 3.7 to 8.0. By combining real-space confocal laser scanning microscop

  17. Geochemistry of colloid systems. For earth scientists

    NARCIS (Netherlands)

    Nickel, E.

    1979-01-01

    The second part of the title of this book gives an indication for whom it has been written. It is a real 'synthesizer'. Throughout ten chapters the reader is introduced into the highly complex matter of colloid chemistry and its role in geochemistry, pedology, oceanography, and geology.

  18. 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

  19. 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.

  20. Dipolar structures in colloidal magnetite dispersions

    NARCIS (Netherlands)

    Klokkenburg, Mark

    2007-01-01

    Dipolar structures in liquid colloidal dispersions comprising well-defined magnetite (Fe3O4) nanoparticles with a permanent magnetic dipole moment are analyzed on a single-particle level by in situ cryogenic transmission electron microscopy (2D). Compared to conventional ferrofluids, these dispersio

  1. 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

  2. Advanced Colloids Experiment (ACE-H-2)

    Science.gov (United States)

    Meyer, William V.; Sicker, Ron; Chmiel, Alan J.; Eustace, John; LaBarbera, Melissa

    2015-01-01

    Increment 43 - 44 Science Symposium presentation of Advanced Colloids Experiment (ACE-H-2) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  3. Advanced Colloids Experiment (ACE-T1)

    Science.gov (United States)

    Meyer, William V.; Sicker, Ron; Brown, Dan; Eustace, John

    2015-01-01

    Increment 45 - 46 Science Symposium presentation of Advanced Colloids Experiment (ACE-T1) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  4. Evolution of Binaries in Dense Stellar Systems

    CERN Document Server

    Ivanova, Natalia

    2011-01-01

    In contrast to the field, the binaries in dense stellar systems are frequently not primordial, and could be either dynamically formed or significantly altered from their primordial states. Destruction and formation of binaries occur in parallel all the time. The destruction, which constantly removes soft binaries from a binary pool, works as an energy sink and could be a reason for cluster entering the binary-burning phase. The true binary fraction is greater than observed, as a result, the observable binary fraction evolves differently from the predictions. Combined measurements of binary fractions in globular clusters suggest that most of the clusters are still core-contracting. The formation, on other hand, affects most the more evolutionary advanced stars, which significantly enhances the population of X-ray sources in globular clusters. The formation of binaries with a compact objects proceeds mainly through physical collisions, binary-binary and single-binary encounters; however, it is the dynamical for...

  5. Directed Self-assembly of Colloidal Particles on a Blue Phase I Interface

    Science.gov (United States)

    Martinez-Gonzalez, Jose; Zhou, Ye; Sadati, Monirosadat; Abbott, Nicholas; de Pablo, Juan

    Blue phases are liquid states of matter with a highly ordered defect structure which confers unique properties among complex fluids. In this work, a free energy model of chiral liquid crystals is used to consider the self-assembly of colloids and nanoparticles on the interface of a Blue Phase I. It is shown that the crystalline defect structure of the blue phase produces intricate, two-dimensional hexagonal and Kagome structures among the nanoparticle arrangements, with lattice parameters that depend on the type of anchoring of the liquid crystal at the particle's surface. These parameters can be tuned via the chirality of the material, thereby offering intriguing possibilities for the creation of hierarchical materials based on the directed assembly of particles in chiral liquid crystals. This work is supported by the Department of Energy, Basic Energy Sciences, Materials Science and Engineering Division, Biomaterials Program, through DE-SC004025.

  6. Electrochromic and photonic devices utilizing polymer colloidal particles

    Science.gov (United States)

    Shim, Goo Hwan

    stop band position of the photonic crystal structure. In addition, this ordered structure could be encapsulated with poly(ethylene glycol) methacrylate (PEGMA) matrix. Optical properties of this solid material possess the same characteristics as colloidal particles. Modifying the emission spectra of hydrogel-encapsulated crystalline colloidal arrays composed of Rhodamine B labeled PS CCA was realized through the mechanochromic tuning of this PCCA structure.

  7. Spin Correlation in Binary Systems

    CERN Document Server

    Farbiash, N; Farbiash, Netzach; Steinitz, Raphael

    2004-01-01

    We examine the correlation of projected rotational velocities in binary systems. It is an extension of previous work (Steinitz and Pyper, 1970; Levato, 1974). An enlarged data basis and new tests enable us to conclude that there is indeed correlation between the projected rotational velocities of components of binaries. In fact we suggest that spins are already correlated.

  8. Evolutionary Memory in Binary Systems?

    CERN Document Server

    Steinitz, N F R

    2004-01-01

    Correlation between the spins (rotational velocities) in binaries has previously been established. We now continue and show that the degree of spin correlation is independent of the components' separation. Such a result might be related for example to Zhang's non-linear model for the formation of binary stars from a nebula.

  9. Relativistic Binaries in Globular Clusters

    Directory of Open Access Journals (Sweden)

    Matthew J. Benacquista

    2013-03-01

    Full Text Available Galactic globular clusters are old, dense star systems typically containing 10^4 – 10^6 stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution that leads to relativistic binaries, and current and possible future observational evidence for this population. Our discussion of globular cluster evolution will focus on the processes that boost the production of tight binary systems and the subsequent interaction of these binaries that can alter the properties of both bodies and can lead to exotic objects. Direct N-body integrations and Fokker–Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

  10. PERIODIC COMPLEMENTARY BINARY SEQUENCE PAIRS

    Institute of Scientific and Technical Information of China (English)

    XuChengqian; ZhaoXiaoqun

    2002-01-01

    A new set of binary sequences-Periodic Complementary Binary Sequence Pair (PCSP)is proposed .A new class of block design-Difference Family Pair (DFP)is also proposed .The relationship between PCSP and DFP,the properties and exising conditions of PCSP and the recursive constructions for PCSP are given.

  11. PERIODIC COMPLEMENTARY BINARY SEQUENCE PAIRS

    Institute of Scientific and Technical Information of China (English)

    Xu Chengqian; Zhao Xiaoqun

    2002-01-01

    A new set of binary sequences-Periodic Complementary Binary Sequence Pair (PCSP) is proposed. A new class of block design-Difference Family Pair (DFP) is also proposed.The relationship between PCSP and DFP, the properties and existing conditions of PCSP and the recursive constructions for PCSP are given.

  12. Relativistic Binaries in Globular Clusters

    Directory of Open Access Journals (Sweden)

    Benacquista Matthew J.

    2006-02-01

    Full Text Available The galactic population of globular clusters are old, dense star systems, with a typical cluster containing 10^4 - 10^7 stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss the theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution which lead to relativistic binaries, and current and possible future observational evidence for this population. Globular cluster evolution will focus on the properties that boost the production of hard binary systems and on the tidal interactions of the galaxy with the cluster, which tend to alter the structure of the globular cluster with time. The interaction of the components of hard binary systems alters the evolution of both bodies and can lead to exotic objects. Direct N-body integrations and Fokker-Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

  13. Relativistic Binaries in Globular Clusters

    Directory of Open Access Journals (Sweden)

    Benacquista Matthew

    2002-01-01

    Full Text Available The galactic population of globular clusters are old, dense star systems, with a typical cluster containing $10^4 - 10^6$ stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss the theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution which lead to relativistic binaries, and current and possible future observational evidence for this population. Globular cluster evolution will focus on the properties that boost the production of hard binary systems and on the tidal interactions of the galaxy with the cluster, which tend to alter the structure of the globular cluster with time. The interaction of the components of hard binary systems alters the evolution of both bodies and can lead to exotic objects. Direct $N$-body integrations and Fokker--Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

  14. Colloid suspension stability and transport through unsaturated porous media

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  15. Signature Visualization of Software Binaries

    Energy Technology Data Exchange (ETDEWEB)

    Panas, T

    2008-07-01

    In this paper we present work on the visualization of software binaries. In particular, we utilize ROSE, an open source compiler infrastructure, to pre-process software binaries, and we apply a landscape metaphor to visualize the signature of each binary (malware). We define the signature of a binary as a metric-based layout of the functions contained in the binary. In our initial experiment, we visualize the signatures of a series of computer worms that all originate from the same line. These visualizations are useful for a number of reasons. First, the images reveal how the archetype has evolved over a series of versions of one worm. Second, one can see the distinct changes between version. This allows the viewer to form conclusions about the development cycle of a particular worm.

  16. Observing binary inspiral with LIGO

    CERN Document Server

    Finn, L S

    1994-01-01

    Gravitational radiation from a binary neutron star or black hole system leads to orbital decay and the eventual coalescence of the binary's components. During the last several minutes before the binary components coalesce, the radiation will enter the bandwidth of the United States Laser Inteferometer Gravitational-wave Observatory (LIGO) and the French/Italian VIRGO gravitational radiation detector. The combination of detector sensitivity, signal strength, and source density and distribution all point to binary inspiral as the most likely candidate for observation among all the anticipated sources of gravitational radiation for LIGO/VIRGO. Here I review briefly some of the questions that are posed to theorists by the impending observation of binary inspiral.

  17. Colloid Mobilization and Transport during Capillary Fringe Fluctuations

    Science.gov (United States)

    Aramrak, Surachet; Flury, Markus

    2016-04-01

    Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead filled column. Confocal images showed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively-charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively-charged colloids did not attach to static air-bubbles, but hydrophobic negatively-charged and hydrophilic positively-charged colloids did.

  18. Efficient Confinement of Ultraviolet Light into the Self-Assembled, Dielectric Colloidal Monolayer on a Flat Aluminum Film

    CERN Document Server

    Lee, Seungwoo

    2014-01-01

    Here we propose the efficient confinement of ultraviolet (UV) light into the plasmonic-photonic crystal hybrid, which can be practically developed by the self-assembly of dielectric colloidal nanosphere monolayer onto a flat aluminum (Al) film. Using a numerical approach, we analyzed modal characteristics of each different resonant mode at the UV wavelengths including surface plasmon polariton (SPP) mode and waveguided (WG) mode and tuned these resonant modes from deep to far UV simply by adjusting the size of dielectric colloidal nanosphere. The calculated quality-factor (Q-factor) of such plasmonic-photonic crystal hybrid is at least one order of magnitude higher than that of the existing Al nanostructures (Al nanoparticles, nanodisks, nanovoids, or nanogratings) standing on the dielectric substrate. Also, we systematically studied how the amount of native oxide, which can be generated during the general process for the deposition of Al, can influence on both the SPP and WG modes of such plasmonic-photonic ...

  19. Cooperative dynamics in ultrasoft 2D crystals

    Science.gov (United States)

    Sprakel, Joris; van der Meer, Berend; Dijkstra, Marjolein; van der Gucht, Jasper

    2015-03-01

    The creation, annihilation, and diffusion of defects in crystal lattices play an important role during crystal melting and deformation. Although it is well understood how defects form and react when crystals are subjected to external stresses, it remains unclear how crystals cope with internal stresses. We report a study in which we create a highly localized internal stress, by means of optical tweezing, in a crystal formed from micrometer-sized colloidal spheres and directly observe how the solid reacts using microscopy. We find that, even though the excitation is highly localized, a collective dance of colloidal particles results; these collective modes take the form of closed rings or open-ended strings, depending on the sequence of events which nucleate the rearrangements. Surprisingly, we find from Brownian Dynamics simulations that these cooperative dynamics are thermally-activated modes inherent to the crystal, and can even occur through a single, sufficiently large thermal fluctuation, resulting in the irreversible displacement of 100s of particles from their lattice sites.

  20. LONG-TERM COLLOID MOBILIZATION AND COLLOID-FACILITATED TRANSPORT OF RADIONUCLIDES IN A SEMI-ARID VADOSE ZONE

    Energy Technology Data Exchange (ETDEWEB)

    Markus Flury; James B. Harsh; Fred Zhang; Glendon W. Gee; Earl D. Mattson; Peter C. L

    2012-08-01

    The main purpose of this project was to improve the fundamental mechanistic understanding and quantification of long-term colloid mobilization and colloid-facilitated transport of radionuclides in the vadose zone, with special emphasis on the semi-arid Hanford site. While we focused some of the experiments on hydrogeological and geochemical conditions of the Hanford site, many of our results apply to colloid and colloid-facilitated transport in general. Specific objectives were (1) to determine the mechanisms of colloid mobilization and colloid-facilitated radionuclide transport in undisturbed Hanford sediments under unsaturated flow, (2) to quantify in situ colloid mobilization and colloid-facilitated radionuclidetransport from Hanford sediments under field conditions, and (3) to develop a field-scale conceptual and numerical model for colloid mobilization and transport at the Hanford vadose zone, and use that model to predict long-term colloid and colloid- facilitated radionuclide transport. To achieve these goals and objectives, we have used a combination of experimental, theoretical, and numerical methods at different spatial scales, ranging from microscopic investigationsof single particle attachment and detachment to larger-scale field experiments using outdoor lysimeters at the Hanford site. Microscopic and single particle investigations provided fundamental insight into mechanisms of colloid interactions with the air-water interface. We could show that a moving air water interface (such as a moving water front during infiltration and drainage) is very effective in removing and mobilizing particles from a stationary surface. We further demonstrated that it is particularly the advancing air-water interface which is mainly responsible for colloid mobilization. Forces acting on the colloids calculated from theory corroborated our experimental results, and confirm that the detachment forces (surface tension forces) during the advancing air-water interface

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-05-15

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

  2. Facile synthesis of small crystal ZSM-5 zeolite by acid-catalyzed hydrolysis of tetraethylorthosilicate

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Small crystal zeolites ZSM-5 with sizes of 150-300 nm were synthesized using the colloidal silicate precursors as the silica source created by the acid-catalyzed hydrolysis of tetraethylorthosilicate with tetrapropylammonium bromide as the structure-directing agent within a short crystallization time of 20-35 h. The precursors and final products were detected by XRD, SEM, ICP and DLS.

  3. 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

  4. Towards Physarum Binary Adders

    CERN Document Server

    Jones, Jeff; 10.1016/j.biosystems.2010.04.005

    2010-01-01

    Plasmodium of \\emph{Physarum polycephalum} is a single cell visible by unaided eye. The plasmodium's foraging behaviour is interpreted in terms of computation. Input data is a configuration of nutrients, result of computation is a network of plasmodium's cytoplasmic tubes spanning sources of nutrients. Tsuda et al (2004) experimentally demonstrated that basic logical gates can be implemented in foraging behaviour of the plasmodium. We simplify the original designs of the gates and show --- in computer models --- that the plasmodium is capable for computation of two-input two-output gate $ \\to $ and three-input two-output $ \\to $. We assemble the gates in a binary one-bit adder and demonstrate validity of the design using computer simulation.

  5. Towards Physarum binary adders.

    Science.gov (United States)

    Jones, Jeff; Adamatzky, Andrew

    2010-07-01

    Plasmodium of Physarum polycephalum is a single cell visible by unaided eye. The plasmodium's foraging behaviour is interpreted in terms of computation. Input data is a configuration of nutrients, result of computation is a network of plasmodium's cytoplasmic tubes spanning sources of nutrients. Tsuda et al. (2004) experimentally demonstrated that basic logical gates can be implemented in foraging behaviour of the plasmodium. We simplify the original designs of the gates and show - in computer models - that the plasmodium is capable for computation of two-input two-output gate x, y-->xy, x+y and three-input two-output x,y,z-->x yz,x+y+z. We assemble the gates in a binary one-bit adder and demonstrate validity of the design using computer simulation.

  6. Eccentric Binary Millisecond Pulsars

    CERN Document Server

    Freire, Paulo C C

    2009-01-01

    In this paper we review the recent discovery of several millisecond pulsars (MSPs) in eccentric binary systems. Timing these MSPs we were able to estimate (and in one case precisely measure) their masses. These results suggest that, as a class, MSPs have a much wider range of masses (1.3 to > 2 solar masses) than the normal and mildly recycled pulsars found in double neutron star (DNS) systems (1.25 < Mp < 1.44 solar masses). This is very likely to be due to the prolonged accretion episode that is thought to be required to form a MSP. The likely existence of massive MSPs makes them a powerful probe for understanding the behavior of matter at densities larger than that of the atomic nucleus; in particular, the precise measurement of the mass of PSR J1903+0327 ($1.67 +/- 0.01 solar masses) excludes several "soft" equations of state for dense matter.

  7. Fabrication of High Quality Three-Dimensional Photonic Crystals

    Institute of Scientific and Technical Information of China (English)

    HU Xiao-Yong; LIU Yuan-Hao; CHENG Bing-Ying; ZHANG Dao-Zhong; MENG Qing-Bo

    2004-01-01

    High quality colloidal photonic crystals made from polystyrene spheres with diameter 240nm are fabricated by the vertical deposition method. The scanning electron microscopy (SEM) and the transmittance spectrum are used to characterize the properties of the photonic crystal. The SEM images show that there are few lattice defects. The transmittance of the photonic crystal is above 75% in the pass band at 700nm and is lower than 5% at the centre of the band gap, respectively. It is found that proper concentration is a very important factor to fabricate the photonic crystal when the diameter of the spheres is lower than 300nm.

  8. Exploring the dynamics of phase separation in colloid-polymer mixtures with long range attraction.

    Science.gov (United States)

    Sabin, Juan; Bailey, Arthur E; Frisken, Barbara J

    2016-06-28

    We have studied the kinetics of phase separation and gel formation in a low-dispersity colloid - non-adsorbing polymer system with long range attraction using small-angle light scattering. This system exhibits two-phase and three-phase coexistence of gas, liquid and crystal phases when the strength of attraction is between 2 and 4kBT and gel phases when the strength of attraction is increased. For those samples that undergo macroscopic phase separation, whether to gas-crystal, gas-liquid or gas-liquid-crystal coexistence, we observe dynamic scaling of the structure factor and growth of a characteristic length scale that behaves as expected for phase separation in fluids. In samples that gel, the power law associated with the growth of the dominant length scale is not equal to 1/3, but appears to depend mainly on the strength of attraction, decreasing from 1/3 for samples near the coexistence region to 1/27 at 8kBT, over a wide range of colloid and polymer concentrations.

  9. Anisometric C60 Fullerene Colloids Assisted by Structure-Directing Agent

    Energy Technology Data Exchange (ETDEWEB)

    Penterman, S. [Cornell Univ., Ithaca, NY (United States); Liddell Watson, Chekesha M. [Cornell Univ., Ithaca, NY (United States); Escobedo, Fernando A. [Cornell Univ., Ithaca, NY (United States); Cohen, Itai [Cornell Univ., Ithaca, NY (United States)

    2016-08-05

    Colloidal synthesis and assembly provide low cost, large area routes to mesoscale structures. In particular, shape-anisotropic particles may form crystalline, plastic crystalline, complex liquid crystalline and glassy phases. Arrangements in each order class have been used to generate photonic materials. For example, large photonic band gaps have been found for photonic crystals, hyperuniform photonic glasses, and also for plastic crystals at sufficient refractive index contrast. The latter structures support highly isotropic bandgaps that are desirable for free-form waveguides and LED out-coupling. Photonic glasses with optical gain lead to self-tuned lasing by the superposition of multiply scattered light. Typically, extrinsic media such as organic dyes, rare earths, lanthanides and quantum dots are used to impart optical gain in photonic solids. The present work advances fullerene microcrystals as a new materials platform for ‘active’ light emitting in colloid-based photonic crystals. Fullerenes support singlet excited states that recombine to produce a characteristic red photoluminescence. C60 also has a high refractive index (n ~ 2.2) and transparency (> 560 nm)9 so that inverse structures are not required.

  10. Comparision of {sup 188}Rhenuim-tin colloid and {sup 188}Rhenium-sulfur colloid as a radiation synovectomy agent

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y. J.; Jung, J. M.; Kim, Y. J.; Jang, Y. S.; Lee, D. S.; Jung, J. K.; Song, Y. W.; Lee, M. C. [KAERI, Taejon (Korea, Republic of)

    1999-10-01

    Beta-emitting radiocolloids have been used for the treatment of rheumatoid arthritis. As a generator produced beta-emitting radionuclide, the importance of Re-188 for radionuclide therapy is increasing rapidly. We compared the radiochemistry of two {sup 188}Re labeled radiocolloids: {sup 188}Re-tin colloid and {sup 188}Re-sulfur colloid. {sup 188}Re-tin colloid was obtained by reacting 10 mg SnCl{sub 2}{center_dot}H{sub 2}O and {sup 188}Re perrhenate. {sup 188}Re-sulfur colloid was labeled by boiling 40 mg sodium thiosulfate, 0.8 mg Na{sub 2}{center_dot}EDTA, and 0.8 mg potassium perrhenate with {sup 188}Re perrhenate. Radiochemical purity was checked by ITLC-SG/ saline. Labeling efficiencies reached >98% for tin colloid at 2 hr and 89{approx}94% for sulfur colloid at 3 hr. All the preparations were stable for 72 hr in water, serum, and synovial fluid. If labeled at higher temperature, particle size of tin colloid increased. Remained radioactivity of {sup 188}Re-sulfur colloid in disposable polypropylene syringe after injecting to mice was high (62.0{+-}7.0%) due to its hydrophobic nature, although, tin colloid did not show high remained radioactivity (2.9{+-}1.6%). Biodistribution in Antigen induced arthratitis model rabbit after synovial space injection showed that {sup 188}Re-tin colloid was well retained in synovial space for 48 hr. Although, both {sup 188}Re-tin colloid and {sup 188}Re-sulfur colloid might be useful for radionuclide therapy, we concluded that {sup 188}Re-tin colloid is more adventageous over {sup 188}Re-sulfur colloid, due to higher labeling efficency, size-controllable property, and lower residual activity in syringe.

  11. Dynamical Evolution of Wide Binaries

    Directory of Open Access Journals (Sweden)

    Esmeralda H. Mallada

    2001-01-01

    Full Text Available We simulate numerically encounters of wide binaries with field stars and Giant Molecular Clouds (GMCs by means of the impulse approximation. We analyze the time evolution of the distributions of eccentricities and semimajor axes of wide binaries with given initial conditions, at intervals of 109 yr, up to 1010 yr (assumed age of the Galaxy. We compute the fraction of surviving binaries for stellar encounters, for GMC encounters and for a combination of both, and hence, the dynamical lifetime for different semimajor axes and different masses of binaries (0.5, 1, 1.2, 1.5, 2.5, and 3 Msolar. We find that the dynamical lifetime of wide binaries considering only GMCs is half than that considering only stars. For encounters with GMCs we analyze the influence of the initial inclination of the orbital plane of the binary with respect to the plane perpendicular to the relative velocity vector of the binary and the GMC. We find that the perturbation is maximum when the angle is minimum.

  12. Chaotic zones around gravitating binaries

    CERN Document Server

    Shevchenko, Ivan I

    2014-01-01

    The extent of the continuous zone of chaotic orbits of a small-mass tertiary around a system of two gravitationally bound bodies (a double star, a double black hole, a binary asteroid, etc.) is estimated analytically, in function of the tertiary's orbital eccentricity. The separatrix map theory is used to demonstrate that the central continuous chaos zone emerges due to overlapping of the orbital resonances corresponding to the integer ratios p:1 between the tertiary and the binary periods. The binary's mass ratio, above which such a chaotic zone is universally present, is also estimated.

  13. Modified evolution of stellar binaries from supermassive black hole binaries

    Science.gov (United States)

    Liu, Bin; Wang, Yi-Han; Yuan, Ye-Fei

    2017-04-01

    The evolution of main-sequence binaries resided in the galactic centre is influenced a lot by the central supermassive black hole (SMBH). Due to this perturbation, the stars in a dense environment are likely to experience mergers or collisions through secular or non-secular interactions. In this work, we study the dynamics of the stellar binaries at galactic centre, perturbed by another distant SMBH. Geometrically, such a four-body system is supposed to be decomposed into the inner triple (SMBH-star-star) and the outer triple (SMBH-stellar binary-SMBH). We survey the parameter space and determine the criteria analytically for the stellar mergers and the tidal disruption events (TDEs). For a relative distant and equal masses SMBH binary, the stars have more opportunities to merge as a result from the Lidov-Kozai (LK) oscillations in the inner triple. With a sample of tight stellar binaries, our numerical experiments reveal that a significant fraction of the binaries, ∼70 per cent, experience merger eventually. Whereas the majority of the stellar TDEs are likely to occur at a close periapses to the SMBH, induced by the outer Kozai effect. The tidal disruptions are found numerically as many as ∼10 per cent for a close SMBH binary that is enhanced significantly than the one without the external SMBH. These effects require the outer perturber to have an inclined orbit (≥40°) relatively to the inner orbital plane and may lead to a burst of the extremely astronomical events associated with the detection of the SMBH binary.

  14. Two-dimensional photonic crystal surfactant detection.

    Science.gov (United States)

    Zhang, Jian-Tao; Smith, Natasha; Asher, Sanford A

    2012-08-07

    We developed a novel two-dimensional (2-D) crystalline colloidal array photonic crystal sensing material for the visual detection of amphiphilic molecules in water. A close-packed polystyrene 2-D array monolayer was embedded in a poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel film. These 2-D photonic crystals placed on a mirror show intense diffraction that enables them to be used for visual determination of analytes. Binding of surfactant molecules attaches ions to the sensor that swells the PNIPAAm-based hydrogel. The resulting increase in particle spacing red shifts the 2-D diffracted light. Incorporation of more hydrophobic monomers increases the sensitivity to surfactants.

  15. Binary Oscillatory Crossflow Electrophoresis

    Science.gov (United States)

    Molloy, Richard F.; Gallagher, Christopher T.; Leighton, David T., Jr.

    1997-01-01

    Electrophoresis has long been recognized as an effective analytic technique for the separation of proteins and other charged species, however attempts at scaling up to accommodate commercial volumes have met with limited success. In this report we describe a novel electrophoretic separation technique - Binary Oscillatory Crossflow Electrophoresis (BOCE). Numerical simulations indicate that the technique has the potential for preparative scale throughputs with high resolution, while simultaneously avoiding many problems common to conventional electrophoresis. The technique utilizes the interaction of an oscillatory electric field and a transverse oscillatory shear flow to create an active binary filter for the separation of charged protein species. An oscillatory electric field is applied across the narrow gap of a rectangular channel inducing a periodic motion of charged protein species. The amplitude of this motion depends on the dimensionless electrophoretic mobility, alpha = E(sub o)mu/(omega)d, where E(sub o) is the amplitude of the electric field oscillations, mu is the dimensional mobility, omega is the angular frequency of oscillation and d is the channel gap width. An oscillatory shear flow is induced along the length of the channel resulting in the separation of species with different mobilities. We present a model that predicts the oscillatory behavior of charged species and allows estimation of both the magnitude of the induced convective velocity and the effective diffusivity as a function of a in infinitely long channels. Numerical results indicate that in addition to the mobility dependence, the steady state behavior of solute species may be strongly affected by oscillating fluid into and out of the active electric field region at the ends of the cell. The effect is most pronounced using time dependent shear flows of the same frequency (cos((omega)t)) flow mode) as the electric field oscillations. Under such conditions, experiments indicate that

  16. Reproducible, high-throughput synthesis of colloidal nanocrystals for optimization in multidimensional parameter space.

    Science.gov (United States)

    Chan, Emory M; Xu, Chenxu; Mao, Alvin W; Han, Gang; Owen, Jonathan S; Cohen, Bruce E; Milliron, Delia J

    2010-05-12

    While colloidal nanocrystals hold tremendous potential for both enhancing fundamental understanding of materials scaling and enabling advanced technologies, progress in both realms can be inhibited by the limited reproducibility of traditional synthetic methods and by the difficulty of optimizing syntheses over a large number of synthetic parameters. Here, we describe an automated platform for the reproducible synthesis of colloidal nanocrystals and for the high-throughput optimization of physical properties relevant to emerging applications of nanomaterials. This robotic platform enables precise control over reaction conditions while performing workflows analogous to those of traditional flask syntheses. We demonstrate control over the size, size distribution, kinetics, and concentration of reactions by synthesizing CdSe nanocrystals with 0.2% coefficient of variation in the mean diameters across an array of batch reactors and over multiple runs. Leveraging this precise control along with high-throughput optical and diffraction characterization, we effectively map multidimensional parameter space to tune the size and polydispersity of CdSe nanocrystals, to maximize the photoluminescence efficiency of CdTe nanocrystals, and to control the crystal phase and maximize the upconverted luminescence of lanthanide-doped NaYF(4) nanocrystals. On the basis of these demonstrative examples, we conclude that this automated synthesis approach will be of great utility for the development of diverse colloidal nanomaterials for electronic assemblies, luminescent biological labels, electroluminescent devices, and other emerging applications.

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

    Science.gov (United States)

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

    2014-11-28

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

  18. Stability of binaries. Part II: Rubble-pile binaries

    Science.gov (United States)

    Sharma, Ishan

    2016-10-01

    We consider the stability of the binary asteroids whose members are granular aggregates held together by self-gravity alone. A binary is said to be stable whenever both its members are orbitally and structurally stable to both orbital and structural perturbations. To this end, we extend the stability analysis of Sharma (Sharma [2015] Icarus, 258, 438-453), that is applicable to binaries with rigid members, to the case of binary systems with rubble members. We employ volume averaging (Sharma et al. [2009] Icarus, 200, 304-322), which was inspired by past work on elastic/fluid, rotating and gravitating ellipsoids. This technique has shown promise when applied to rubble-pile ellipsoids, but requires further work to settle some of its underlying assumptions. The stability test is finally applied to some suspected binary systems, viz., 216 Kleopatra, 624 Hektor and 90 Antiope. We also see that equilibrated binaries that are close to mobilizing their maximum friction can sustain only a narrow range of shapes and, generally, congruent shapes are preferred.

  19. Theory of Electrorotation of Clustered Colloidal Particles

    Institute of Scientific and Technical Information of China (English)

    LIU Ren-Ming; HUANG Ji-Ping

    2005-01-01

    When a colloidal suspension is exposed to a strong rotating electric field, an aggregation of the suspended particles is induced to appear. In such clusters, the separation between the suspended particles is so close that one could not neglect the multiple image effect on the electrorotation (ER) spectrum. Since so far the exact multiple image method exists in two dimensions only, rather than in three dimensions, we investigate the ER spectrum of the clustered colloidal particles in two dimensions, in which many cylindrical particles are randomly distributed in a sheet cluster. We report the dependence of the ER spectrum on the materialparameters. It is shown that the multiple image method predicts two characteristic frequencies, at which the rotation speed reaches maximum. To this end, the multiple image method is numerically demonstrated to be in good agreement with the known Maxwell-Garnett approximation.

  20. Collective motion in populations of colloidal robots

    Science.gov (United States)

    Bartolo, Denis; Bricard, Antoine; Caussin, Jean-Baptiste; Dauchot, Olivier; Desreumaux, Nicolas

    2014-03-01

    Could the behavior of bacteria swarms, fish schools, and bird flocks be understood within a unified framework? Can one ignore the very details of the interaction mechanisms at the individual level to elucidate how strikingly similar collective motion emerges at the group level in this broad range of motile systems? These seemingly provocative questions have triggered significant advance in the physics and the biology, communities over the last decade. In the physics language these systems, made of motile individuals, can all be though as different realizations of ``active matter.'' In this talk, I will show how to gain more insight into this vivid field using self-propelled colloids as a proxy for motile organism. I will show how to motorize colloidal particles capable of sensing the orientation of their neighbors. Then, I will demonstrate that these archetypal populations display spontaneous transitions to swarming motion, and to global directed motion with very few density and orientation fluctuations.