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Simple synthesis methods for mesoporous fibers and powders by rapid evaporation of hydrolyzed silicon alkoxide−surfactant solutions are described. Mesoporous fibers are prepared by dry spinning, and mesoporous powders by spray drying of alkoxide−surfactant solutions. Precursor solutions, containing fully hydrolyzed tetraethoxysilane, cetyltrimethylammonium chloride surfactant, and, in the case of the fibers, a fiber-forming polymer, in an acidic alcohol/water mixture, are drawn into continuous filaments or atomized into droplets in a heated air stream. During solvent drying, silica and surfactant self-assemble to form the hexagonally ordered mesophase structure, and all of the nonvolatile components (silica, polymer, and surfactant) are incorporated into the mesophase. The pore diameter and surface area of calcined fibers were 20 A and 1100 m2/g, respectively. For the powders, pore sizes of 25 A and surface areas as high as 1770 m2/g were measured. Spray-dried powders consisting of hollow spherical partic...

Bimodal suspensions of nanometer-sized boehmite particles and micron-sized gibbsite particles in 0.10MNaNO3are used as models to gain insight into the physical properties of agglomerating colloidal suspensions containing bimodal distributions of primary particles. Results on the gibbsite–boehmite mixtures show that the presences of small particles in a suspension can have a dramatic impact on the rheological, sedimentation, and filtration characteristics of suspensions of larger particles. Transmission electron micrographs show that boehmite forms a coating on the larger gibbsite particles. The coating provides steric repulsion and reduces the attractive interactions between the larger particles, leading to viscosity decreases and greater densification of sediments and filter cakes. A model has been developed to rationalize observed property changes based on the range of agglomerate structures that can form in mixtures of large and small particles. Results are discussed in the content of the processing of nuclear waste sludges, but are applicable to a wide range of bimodal suspensions.

Polyion complexes of arachidic acid and poly (ethyleneimine) were deposited onto Celgard 2400 microporous support membranes and the permeabilities of carbon dioxide and nitrogen through these composite membranes were measured at elevated temperatures. While nitrogen is relatively inert, carbon dioxide tends to have a high solubility in the hydrophilic polymer and the resulting difference in the permeabilities of carbon dioxide and nitrogen can be used to characterize solution-diffusion permeation. Room-temperature gas permeabilities were consistent with Knudsen diffusion through holes or defects. At elevated temperatures the permeabilities of carbon dioxide increased sharply while those of nitrogen increased only moderately indicating that the solution-diffusion mechanism became competitive with Knudsen diffusion. Room-temperature reflection and transmission IR spectra of films on separate substrates indicated that the alkyl tails of the fatty acid were oriented parallel with the surface normal and were packed hexagonally. At elevated temperatures, the tails and the carboxylate head groups disordered with increasing temperature. The disordering was correlated with the sharp increase in the carbon dioxide permeability.

Ferric stearate and ferric complexes were successfully deposited onto porous support membranes. Langmuir-Blodgett (LB) films of ferric stearate greatly reduced the permeabilities of carbon dioxide and nitrogen through the membrane. Above 65°C, a time-dependent change in the LB film leads to a permeability increase. Permeation through ferric stearate alone was mostly due to a Knudsen diffusion mechanism. LB films selective for carbon dioxide were made by co-depositing poly(2-vinylpyridine) with ferric stearate and with the ferric salt of poly(maleic anhydride 1-octadecene).

An amphoteric surfactant templating route permits the synthesis of hexagonal mesophases of zirconium compounds by self-assembly of the surfactant and soluble zirconium species in aqueous solution.