Preparation and Characterization of Three-dimensionally Ordered Crystalline Macroporous CeO2

Three-dimensional ordered macroporous (3DOM) materials are of great potential importance in catalysis, selective separation, sensor arrays and communications with optical band gaps1. Many results in the synthesis of 3DOM materials have been reported, such as closed-packed silica spheres or polystyrenes (PS) templating routes for silica2, metal oxides1-6 and metals7. Recently, poly(methyl methacrylate) (PMMA) colloidal crystal templates have been used to prepare 3DOM materials of metals8,…     

Dissipative structures formed in the course of drying the colloidal crystals of silica spheres on a cover glass

Macroscopic and microscopic dissipative structural patterns formed in the course of drying the deionized aqueous colloidal crystal suspensions of silica spheres (diameter: 103 nm) on a cover glass have been observed. Spoke-like and ring-like patterns are formed in the macroscopic scale; the former is the crack in the sphere film and the latter is the hill accumulated with spheres formed around the outside edge. The neighbored inter-spoke angle, thickness of the film, and other morphological parameters have been discussed as a function of sphere concentration, concentration of sodium chloride, and the inclined angle of the cover glass. Fractal patterns of the mud cracks are observed in the microscopic scale. Capillary forces between spheres at the air-liquid surface and the relative rates between the water flow at the drying front and the convection flow of spheres are important for the pattern formation. Electronic Publication     

A critical reappraisal of recent communications on the hydrodynamic characterization of silica (aerosil) hydrosols

Different results from recent communications on the hydrodynamic characterization of ultrasonicated silica (®Aerosil) hydrosols led to a critical reappraisal of the data.It can be concluded that the degree of dispersion achievable in pyrogenic (Aerosil) hydrosols by ultrasonication is highly sensitive to the detailed parameters of the dispersion process. Characterization in terms ofabsolute numbers of a limiting particle morphology, corresponding to minima of aggregate size, porosity and number of primary particles in the aggregate is not possible.The most straightforward approach for hydrodynamic characterization seems to be a combination of sedimentation and diffusion data.Other approaches using a combination of sedimentation and viscosity data underestimate the particle dimensions. Moreover, they are quite arbitrary since the final result depends upon the proper choice between several equations for fitting the viscosity concentration dependence; the most rigorous approach seems to be an extended Einstein equation which has recently been adapted to particle aggregates.     

Nonequilibrium Brownian dynamics simulations of shear thinning in concentrated colloidal suspensions

The effect of interparticle forces on shear thinning in concentrated aqueous and nonaqueous colloidal suspensions was studied using nonequilibrium Brownian dynamics. Hydrodynamic interactions among particles were neglected. Systems of 108 particles were studied at volume fractions of 0.2 and 0.4. For the nonaqueous systems, shear thinning could be correlated with the gradual breakup of small flocs present because of the weak, attractive secondary minimum in the interparticle potential. At the highest shear rate for=0.4, the particles were organized into a hexagonally packed array of strings. For the strongly repulsive aqueous systems, the viscosity appeared to be a discontinuous function of the shear rate. For=0.4, this discontinuity coincided with a transition from a disordered state to a lamellar structure for the suspension.     

Phase separation dynamics in driven diffusive systems

We study phase separation dynamics in a driven diffusive system. Our simulations are based on the Cahn-Hilliard equation with an additional flux term due to an external field. We study the dynamical scaling parallel and perpendicular to the field. A crossover is observed from isotropic domains at early times to extremely anisotropic domains at later times. We find that the inverse interfacial density (an isotropic measure of the domain size) increases ast , with =1/3, from early times independent of the field strength, even though we do not observe dynamical scaling during these times. Our results indicate that a growth exponent =1/3 may be more universal than previously expected. We analyze the dynamics in terms of surface driven instabilities and one-dimensional solitary waves.     

An effective cross-linking of polymer layer on monodisperse, poly(maleic anhydride-styrene)-modified colloidal silica particles and properties of the composite

Summary  The cross-linkings of the surface polymer layer on mono disperse, poly(maleic anhydride-styrene)-modified silica particles by the reaction with diisocyanate were studied. The extent of cross-linking was estimated by the weight decrease by immersing the particles in the buffer solution of pH 2.0, 4.0 and 9.0 at a room temperature for 24 h. The reaction of the polymer-modified silica with 1,6-diisocyanatohexane afforded relatively stable composite particles which lost less than 5 wt% of the polymer in aqueous solution in the pH range 2.0–9.0. The diisocyanate was a preferable cross-linker to 2,4-diisocyanatotoluene in terms of stability in acidic or basic aqueous solution. The flexibility of the cross-linker molecule possibly plays an important role in the cross-linking reaction. The carboxyl and amino groups were formed by treating the cross-linked composite particles with diluted HCl solution; 5–6 and 0.5–1.1 μmol g^-1, respectively. The cross-linked composite particles exhibited the characteristic property of ζ-potential, −44 to −47 mV and −102 to −107 mV in a neutral aqueous solution and ethanol, respectively. Received: 26 May 1997 Accepted: 4 August 1997     

Effect of Electrode Pattern on the Column Structure and Yield Stress of Electrorheological Fluids

For electrorheological (ER) suspensions, the aggregate structures of particles were observed in electric fields by the use of transparent cells with different electrode patterns. Although the suspension is dispersed to noninteracting particles without electric fields, many aggregates are formed on the electrode surface in electric fields. Since the dipole–dipole interactions cause chain structures of particles and equilibrium conformations of chains are always aligned with electric field, the aggregates indicate the presence of columns spanning the electrode gap. The particle concentration in columns which are developed between parallel-plate electrodes is about 22 vol %. In striped electrodes, the particles construct striped aggregates along the electrodes and no particles remain in the insulating region. The particle concentration in striped aggregates is about 35 vol %. The nonuniformity of electric field is responsible for the high particle concentration. The increase in particle concentration of column lead to the high yield stress of electrified suspension. Therefore, the ER performance of suspension as an overall response can be improved by the electrode design.     

The first example of anodic corrosion of Pd in aqueous ethylenediamine with formation of colloidal palladium

For the first time, corrosion of a Pd anode was detected during electrolysis in a weakly alkaline aqueous solution of ethylenediamine. The kinetics and mechanism of the process were investigated by the methods of cyclic voltammetry and gravimetry. Scanning electron microscopy showed corrosion of the Pd anode and deposition of Pd on the cathode surface, while the formation of colloidal Pd in the working solution was identified by transmission electron microscopy.     

Dimerization of Colloidal Particles through Controlled Aggregation for Enhanced Properties and Applications

Devising syntheses capable of precisely manipulating matter on the nanoscale is central to many areas of research. The underlying motivation is fueled by the fact that at the nanometer scale, the property has a strong correlation with the structure. One such nanostructure that has accrued much attention is the dimer—a structure composed of two colloidal particles separated by a small gap. This Focus Review discusses how colloidal stability can be strategically manipulated to induce dimerization, together with effective purification steps to further improve yields. We conclude the article by providing representative examples for how dimers composed of plasmonic nanoparticles leads to structures with tunable optical properties and strong electric near‐fields, ideal for application in surface‐enhanced Raman spectroscopy.