Development of materials with ordered structure through phase separation of inorganic-organic mixed sol-gel system

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A method of preparing silica gels with micrometer-range inte-rconnected pores by hydrolyzing alkoxysilanes under coexistence of water-soluble polymers has been investigated in detail. Following results have been obtained ;1. Many kinds of water-soluble polymers that have substantial solubility in--water-alcohol mixed solvent can be used in the process.2. Hydrolysis of alkoxysilanes under strongly acidic condition is favored but polycondensation may be conducted also under more basic condition.3. Light scattering profiles of gelling solution exhibited first a continuous development of concentration fluctuation with a fixed periodic wavelength, second a parallel increase of fluctuation and periodic wavelength, and finally a fixation of periodic wavelength and further increase of concentra tion difference. These changes indicate a concurrent occurrence of spinodal decomposition and sol-gel transition in the reacting system.4. Morphology of gels can be controlled by changing starting composition and reaction temperature. Reaction conditions which make a phase separation to occur earlier relative to a sol-gel transition result in coarse morphologies and vice versa. Polymers with high solubility in water-alcohol mixed solvent are favored to obtain gel morphologies with better reproducibility.5. By exchanging solvent phase in wet gels with micrometer-range interconnected pores, the volume and distribution of nanometer-range pores can be, modified to a large extent. This process enables one to tailor pore structure of gels both in micrometer- and nanometer-ranges.