Formation of metallic and metal hydrous oxide dispersions

The formation, via hydrothermally induced precipitation from homogeneous solution, of a variety of well-defined dispersions of metallic and hydrous metal in the conditions under which the particles are produced (e.g., pH and composition of the growth medium, aging temperature, rate of heating, or degree of agitation) can be readily discerned by following changes in the mass, composition, and morphology of the final solid phase. The generation of colloidal dispersions in the absence of gravity convection or sedimentation effects may result in the appearance of morphological modifications not previously observed in terrestrially formed hydrosols

Preparation and characterization of nanocomposites of natural rubber with polystyrene and styrene-methacrylic acid copolymer nanoparticles

Composites of natural rubber (NR)/vinyl polymer nanoparticles as polystyrene (PS) and poly(styrenemethacrylic acid) (P(S-MAA)) were prepared by heterocoagulation technique. The polymer nanoparticles were prepared by emulsifier-free emulsion polymerizations at 70°C using potassium persulfate as initiator. Under acidic condition where positive charge was present on the NR latex (NRL) surface, the nanoparticles having negative charge mainly from sulfate group of initiator were able to adsorb on the NRL surface, the electrostatic interaction being the driving force. The scanning electron micrographs showed that the polymer nanoparticles are homogenously distributed throughout NR matrix as nanoclusters with an average size of about 500 and 200 nm for PS and P(S-MAA), respectively. The mechanical properties of NR/PS and NR/P(S-MAA) composite films were compared with the NR host. The nanocomposites, particularly when the polymer nanoparticles are uniformly dispersed, possess significantly enhanced mechanical properties strongly depending on the morphology of the nanocomposites

Heterocoagulation-spray drying process for the inclusion of ceramic pigments

The improvement of the physico-chemical resistance of hematite pigment in ceramic bodies has been pursued through its inclusion into a transparent and refractory matrix of silica or zirconia. The inclusion process was accomplished by heterocoagulation followed by spray-drying. The heterocoagulation process was optimised through an electrokinetic technique, that measured the potential of both matrix and pigment as a function of pH and of different amounts of dispersing agents. Suspensions of pigment and matrix were designed in order to achieve the maximum surface charges. The heterocoagulated mix was then spray-dried in order to avoid any separated coagulation of pigment and matrix and to obtain a well granulated powder suitable for application in ceramic bodies. A stable red-coloured ceramic pigment for low firing applications was obtained starting from amorphous silica as matrix and hematite as colorant

Kinetics of Shear Coagulation of Oppositely Charged Particles : A Trajectory Analysis

Transport properties of aqueous colloidal dispersions are controlled by the coagulation of particles in the dispersions. In order to study the coagulation kinetics and stability of colloid in a shear flow, which are practically important, trajectory analyses with electric double layer force have been used. So far, however, this analysis has not been applied to the heterocoagulation between oppositely charged particles in a shear flow. In the present study, the rate of shear coagulation of oppositely charged particle was calculated using the trajectory analysis. The calculated results indicate that the rate of heterocoagulation increases with decreasing ionic strength and increasing the magnitude of surface potential. The increase of the rate is considered to be due to the increases of the thickness of diffuse double layer and the magnitude of attractive double layer force

A mechanistic investigation of Pickering emulsion polymerization

Pickering emulsion polymerization offers a versatile way of synthetising hybrid core–shell latexes where a polymer core is surrounded by an armour of inorganic nanoparticles. A mechanistic understanding of the polymerization process is limited which restricts the use of the technique in the fabrication of more complex, multilayered colloids. In this paper clarity is provided through an in-depth investigation into the Pickering emulsion polymerization of methyl methacrylate (MMA) in the presence of nano-sized colloidal silica (Ludox TM-40). Mechanistic insights are discussed by studying both the adsorption of the stabiliser to the surface of the latex particles and polymerization kinetics. The adhesion of the Pickering nanoparticles was found not to be spontaneous, as confirmed by cryo-TEM analysis of MMA droplets in water and monomer-swollen PMMA latexes. This supports the theory that the inorganic particles are driven towards the interface as a result of a heterocoagulation event in the water phase with a growing oligoradical. The emulsion polymerizations were monitored by reaction calorimetry in order to establish accurate values for monomer conversion and the overall rate of polymerizations (Rp). Rp increased for higher initial silica concentrations and the polymerizations were found to follow pseudo-bulk kinetics

Vertical drying of a suspension of sticks: Monte Carlo simulation for continuous two-dimensional problem

The vertical drying of a two dimensional colloidal film containing zero-thickness sticks (lines) was studied by means of kinetic Monte Carlo (MC) simulations. The continuous two-dimensional problem for both the positions and orientations was considered. The initial state before drying was produced using a model of random sequential adsorption with isotropic orientations of the sticks. During the evaporation, an upper interface falls with a linear velocity in the vertical direction and the sticks undergo translational and rotational Brownian motions. The MC simulations were run at different initial number concentrations (the numbers of sticks per unit area), $p_i$, and solvent evaporation rates, $u$. For completely dried films, the spatial distributions of the sticks, the order parameters and the electrical conductivities of the films in both the horizontal, $x$, and vertical, $y$, directions were examined. Significant evaporation-driven self-assembly and stratification of the sticks in the vertical direction was observed. The extent of stratification increased with increasing values of $u$. The anisotropy of the electrical conductivity of the film can be finely regulated by changes in the values of $p_i$ and $u$.Comment: 10 pages, 8 figures, 47 references, submitted to PR

凝集したナトリウム型モンモリロナイト懸濁液の準希薄状態における沈降挙動

この博士論文は内容の要約のみの公開（または一部非公開）になっています筑波大学 (University of Tsukuba)201