Adhesion of Colloidal SiO(2) Particles on ZnS-Type Phosphor Surfaces

The interaction between colloidal SiO(2) particles and the surface of ZnS-type phosphors has been studied. The green emitting phosphor ZnS:Cu,Al,Au applied in color television tubes was chosen as a model compound. After the surface of the phosphor particles (d(50)=5.0 μm) was treated in different manners like washing with H(2)O, HCl, or H(2)O(2) as well as precoating with colloidal ZnO particles (d(50)=81 nm), colloidal SiO(2) particles (d(50)=207 nm) were added. Thereafter, the amount of adhered SiO(2) was investigated based on SEM and ESCA analysis. By ESA measurements the surface charge of the colloids and the differently treated ZnS materials was investigated. Based on the experimental results it can be concluded that colloidal SiO(2) particles adhere sufficiently only if ZnO is present on the ZnS surface. The SiO(2) particles are located on top of the ZnO. Finally, the attractive interactions in the system ZnS-ZnO-SiO(2) are discussed in more detail. Copyright 2000 Academic Press.     

Simulation of the Adhesion of Particles to Surfaces

The removal of micrometer and submicrometer particles from dielectric and metal films represents a challenge in postchemical mechanical polishing cleaning. Proper modeling of the adhesive force between contaminant particles and these films is needed to develop optimal solutions to postchemical mechanical polishing cleaning. We have previously developed and experimentally validated a model to describe the adhesion between spherical particles and thin films. This simulation expands previous models to characterize the adhesive interaction between asymmetrical particles, characteristic of a polishing slurry, and various films. Our simulation accounts for the contact area between particles and substrates, as well as the morphology of the surfaces. Previous models fail to accurately describe the contact of asymmetrical particles interacting with surfaces. By properly accounting for nonideal and geometry and morphology, the simulation predicts a more accurate adhesive force than predictions based upon an ideal van der Waals model. The simulation is compared to experimental data taken for both semi-ideal particle-substrate systems (polystyrene latex spheres in contact with silicon films) and asymmetrical systems (alumina particles in contact with various films). Copyright 2001 Academic Press.     

Adhesion Probability of Colloidal Particles with Repulsive Soft Interaction

Computer simulations of the irreversible adhesion of charged colloidal particles at a solid/liquid interface are performed to determine whether the distribution of particles in the vicinity of a preadsorbed (also charged) one follows the Boltzmann law applied to ana prioriuniform adhesion probability, as first assumed by Adamczyket al.(J. Colloid Interface Sci.140, 123 (1990)). If true, this would indicate that the whole information on the deposition process is contained in the potential energy distribution on the adsorbing surface. In general, diffusion in a field of force and the irreversibility of the process induce significant deviations from the Boltzmann-weighted uniform adhesion density. Nevertheless, it is shown that for particles characterized by a small gravitational energy this procedure leads to a reasonable first approximation of the distribution of the particles over the adsorbing surface. This observation thus demonstrates the validity of Adamczyk's assumption and extends its range of applicability to the case of a weak gravitational field.     

Tunable Self-Assembly of Diblock Copolymers into Colloidal Particles with Triply Periodic Minimal Surfaces

We herein report the tunable self-assembly of simple block copolymers, namely polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers, into porous cubosomes with inverse or mesophases of controlled unit cell parameters as well as hexasomes with an inverse hexagonal (p6mm) structure, which have been rarely observed in polymer self-assembly. A new morphological phase diagram was constructed for the solution self-assembly of PS-b-PEO based on the volume fraction of the PS block against the initial copolymer concentration. The formation mechanisms of the cubosomes and hexasomes have also been revealed. This study not only affords a simple system for the controllable preparation and fundamental studies of ordered bicontinuous structures, but also opens up a new avenue towards porous architectures with highly ordered pores.     

Silica Coating on Colloidal Maghemite Particles

Maghemite colloidal particles are coated with a silica layer using a silicon alkoxide as silica precursor. The coating process is studied by electrophoresis, quasi-elastic light scattering, nitrogen adsorption, and infrared spectrometry analyses. The conditions of complete coverage of the iron oxide particles by silica and the nature of the maghemite–silica interface are discussed.     

Tunable Self‐Assembly of Diblock Copolymers into Colloidal Particles with Triply Periodic Minimal Surfaces

We herein report the tunable self‐assembly of simple block copolymers, namely polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) diblock copolymers, into porous cubosomes with inverse or mesophases of controlled unit cell parameters as well as hexasomes with an inverse hexagonal (p 6mm ) structure, which have been rarely observed in polymer self‐assembly. A new morphological phase diagram was constructed for the solution self‐assembly of PS‐b‐PEO based on the volume fraction of the PS block against the initial copolymer concentration. The formation mechanisms of the cubosomes and hexasomes have also been revealed. This study not only affords a simple system for the controllable preparation and fundamental studies of ordered bicontinuous structures, but also opens up a new avenue towards porous architectures with highly ordered pores.     

Magnetic Hetero-flocculation of Paramagnetic Colloidal Particles

The feasibility of a high-gradient magnetic separation process, utilizing magnetite as the energizable element in lieu of stainless steel wool, is evaluated by means of an equilibrium, two-particle, magnetic hetero-flocculation model. The model calculates the net force, defined as the sum of the magnetic, electrostatic, and van der Waals forces, exerted on a paramagnetic nanoparticle that is in the proximity of a fixed magnetite particle. Since the nanoparticle-magnetite system is assumed to be in direct contact with the moving fluid, the influence of the hydrodynamic force on the magnetic attractive force between the two particles is also explored. This model clearly reveals the ranges and conditions over which each of these various forces contributes to the net force relative to Brownian (thermal) motion. The model also reveals the feasibility of using magnetite particles instead of stainless steel as the energizable element for high-gradient magnetic separation. Important variables investigated include the size and surface charge of the particles, the magnetic field, the flow velocity, the electrolyte concentration, and the magnetic susceptibility of the nanoparticle. Copyright 2000 Academic Press.     

Colloidal transition-metal-doped ZnO quantum dots

Methods for introducing new magnetic, optical, electronic, photophysical, or photochemical properties to semiconductor nanocrystals are attracting intense applications-oriented interest. In this communication, we report the preparation and electronic absorption spectroscopy of colloidal ZnO DMS-QDs. Our synthetic procedure involves modification of literature methods known to yield highly crystalline and relatively monodisperse nanocrystals of pure ZnO to allow introduction of transition-metal dopants. We use ligand-field electronic absorption spectroscopy as a dopant-specific optical probe to monitor dopant incorporation during nanocrystal growth and to verify internal substitutional doping in Co2+:ZnO and Ni2+:ZnO DMS-QDs. To the best of our knowledge, these are the first free-standing oxide DMS-QDs reported. The synthesis of colloidal oxide DMS-QDs introduces a new category of magnetic semiconductor materials available for detailed physical study and application in nanotechnology.     

Electrokinetic Properties of Fuzzy Colloidal Particles

The presence of a thin polymer layer on the surface of a colloidal particle can have a profound effect on its electrophoretic mobility. The model developed here treats the hydrodynamics of the polymer layer as a distribution of Stokes resistance centers within a thin diffuse layer; fixed charge may reside on the surface of the particle core or throughout the layer. The theory is semianalytical in that asymptotic methods are used to simplify the equations but several integrals must be evaluated numerically. Special attention is paid to the effects of polarization and relaxation. It is shown that distributing immobile charge throughout the layer produces a response where the particle's mobility exceeds that found when the same amount of charge is spread uniformly over the surface of the rigid core. Increasing the drag due to the fuzzy layer always diminishes the mobility. In either case, the hydrodynamic permeability of the layer has a strong influence on particle movement. Results are also given for the dipole coefficient in the expression for the conductivity of a dilute suspension. Copyright 2000 Academic Press.     

光响应细胞粘附界面

光响应分子的响应过程可以通过简单调控光源波长、光强度以及曝光时间进行调节,近年来基于光响应分子构建的智能界面被越来越多地应用于调控细胞粘附行为。目前,用于构筑调控细胞粘附行为的光响应智能界面的功能分子主要有偶氮苯、螺吡喃以及它们的衍生物。基于这些光响应功能分子的光致异构化,光响应智能界面会发生物理化学性质转变,进而实现可控的细胞粘附和去粘附。设计光控细胞粘附界面为研究细胞粘附、迁移以及细胞诊断提供了一种新型便捷的策略。     

Adhesion between Nanoscale Rough Surfaces

In this investigation, the adhesion between particles and plates with root-mean-square, rms, surface roughness of 0.17-10.5 nm was measured by atomic force microscopy. Measurements obtained with particles both larger and smaller than the surface asperities are presented. Results indicate adhesion force decreases sharply with increasing surface roughness in the nanometer scale (<2 nm), followed by a gradual and slow decrease with further increase in roughness. Existing models were found to significantly underestimate adhesion force. Hence, a new model based on a geometry that considers both the height and breadth of asperities yielding an increased asperity radius compared to previous approaches, as detailed in Part I of this series, is applied using both van der Waals and elastic deformation/work of adhesion based approaches. For the system studied in this investigation, the adhesion forces predicted by the proposed model are considerably more accurate than those predicted by past models. Copyright 2000 Academic Press.     

Influence of Sedimentation on Crystallization of Charged Colloidal Particles

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions on dynamic behavior of a colloidal system. Experiments on crystallization of charged colloidal microspheres with di-ameter of 98 nm dispersed in density-matched and -unmatched media (mixtures of H₂O and D₂O in proper proportion) are compared to examine the influence of sedimentation. Reflection spectra of colloidal suspensions were used to monitor the crystallization process. Results showed that the crystal size of the density-unmatched (namely, in the presence of sedimentation) sample grew faster than that of the density-matched (in the absence of sedi-mentation) case at the initial stage of the crystallization, and then the latter overtook and outstripped the former. To explain these observations, we assume that in the settling of crystals sedimentation facilitates result in more particles getting into the crystal structures. However, as the crystals increase to varying sizes, the settling velocities become large and hydrodynamic friction strips off some particles from the delicate crystal structures. Overall, the sedimentation appears to accelerate the crystal size growth initially and then retard the growth. In addition, the crystal structures formed under microgravity were more closely packed than that in normal gravity.     

Polymer Polydispersity Effect on Depletion Interaction between Colloidal Particles

The effect of polymer polydispersity on the polymer‐induced interaction between colloidal particles due to non‐adsorbing ideal chains is investigated. An analytical theory is developed for the polymer‐segment density between two plates and in the space surrounding two spheres by extending a recently proposed superposition approximation to include polymer polydispersity. Monte Carlo computer simulations were made to test the validity of the analytical theory. The polymer densities predicted by the superposition approximation are in reasonable agreement with simulation results for the polydisperse case. The simulations show that depletion leads to a size fractionation of the polymers. It is shown that size polydispersity has a small effect on the interaction between two parallel plates but a more significant effect on the interaction between two spheres. The range of the potential increases and the contact potential drops with increasing polydispersity.

Polymer‐segment density as a function of y for three values of x, as indicated, in the space surrounding two colloidal spheres with radius R = R_g0 and h = 0.48R_g0. Symbols are the MC results: polydisperse polymer (○; z = 1) and monodisperse polymer (•) samples. Curves are the predictions of the product‐function approximation for monodisperse polymer (solid lines) and polydisperse polymer (z = 1, dashed lines).     

醇对均匀胶体粒子形成的影响

Alcohols extremely affect the formation of uniform colloidal particles in the hydrolysis of ferric ions for Fe(NO_3)_3-HNO_3 system. The affecting ability of the alcohols decreases by the order: 2-propanol, ethanol, t-butylalcohol, 1-propanol and n-butanol. The uniform colloidal particles could prepare in the aging solutions containing lower concentration of Fe(NO_3)_3 and higher concentration of HNO_3 in the presence of alcohols comparing with that in the absence of alcohols. The shapes and sizes of the particles formed depend not only on the concentrations of Fe(NO_3)_3 and HNO_3, but also the content of alcohols. In general, lower saturation of precipitating species favours the formation of spherical particles, and high saturation for the elliptic ones.     

以胶体粒子为模板制备核壳纳米复合粒子

核壳纳米复合粒子具有许多不同于单组分胶体粒子的独特的光、电、磁、催化等物理与化学性质,是构筑新型功能复合材料的重要组元,在光子带隙材料、微波吸收材料、电磁流变液、催化剂和生物等领域有重要应用.本文从控制核壳复合粒子的微观结构及壳层均匀性与厚度的角度,详细评述了目前以胶体粒子为模板制备粒径从纳米到微米尺度的核壳复合粒子的方法.指出利用胶体粒子模板表面与壳层物质或其前驱物间的特殊相互作用(包括静电和化学相互作用),是完善现有制备方法和发展新方法来制备具有设定组成、结构和性能的核壳复合粒子的关键,同时也是将来的粒子表面纳米工程和获取有序的、先进纳米复合材料的主要方向。     

Formation of CuI Colloidal Particles in Aqueous Solution

Morphology, structure, and optical properties of ultradisperse CuI particles synthesized in the presence of water-soluble polymers [poly(vinyl alcohol) and gelatin] are studied. It is shown that forming CuI particles are roundish with the sizes varying from 5 to 20 nm. The particles form the aggregates whose shapes and sizes are governed by the nature of stabilizing agent. It is established that, in the presence of gelatin, CuI nanoparticles of hexagonal and cubic modifications are formed, while in the presence of poly(vinyl alcohol), particles only of cubic modification. The studied CuI colloidal solutions are stable with respect to aggregation over long time; however, during their aging at room temperature, morphological and structural properties of CuI nanoparticles are changed.     

Clustering of Particles in Colloidal and Molecular Fluids

Abstract

A review is given of the nature and implications of cluster formation in colloidal and molecular systems. We consider large clusters that can be described in terms of the fractal dimension and percolation exponents. The role of computer molecular simulation is discussed as a new method for probing random clustering of particles, short range structural correlations being of diminished importance here.     

SiO2胶体颗粒的三维有序自组装

由SiO2胶体颗粒的三维有序自组装可以得到面心立方三维结构,它具有折射率周期性变化的特点。它的制备涉及胶体化学、材料科学等学科的前沿领域。其自组装方法包括胶体颗粒的沉降自组装、胶体颗粒在物体限制下的自组装、胶体颗粒的连续对流自组装和利用胶体颗粒表面电性质的自组装。本文对这些组装方法进行了介绍。