Development of bio-science materials by designing porous structure and surface property of oxide gels.

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Silica gels with controlled interconnected pores in micrometer range have been prepared by hydrolyzing alkoxysilane in the presence of a certain kind of water-soluble polymer using acetic acid as a catalyst. The time-resolved laser light scattering measurements of gelling solution revealed that the interconnected structure is developed when the phase separation by the spinodal mechanism and the sol-gel transition take place almost concurrently. The soaking of gels, prior to the evaporation of the solvent, in ammonia solutions with various concentration and volume ratio to the gel piece at various temperatures resulted in the modification of nanometer range pore structures into well-defined mesopores up to 20nm in diameter, after appropriate drying and heat-treatment. The higher the ammonia concentration, and the higher the soaking temperature, the larger the pore size became. When the soaking was carried out with smaller volume of solvent against a gel piece, the structural change was retarded. This result indicates that the dissolution of silica from the wet gel surface into the external solvent is the rate determining step of the whole structure evolution due to dissolution and re-precipitation of silica. The soaking treatment could completely eliminate the micropores in the gel specimen. An evaluation of silica monoliths having double pore sturcures thus prepared was carried out as a chromatographic column material. After chemical modification of hydrophilic silica gel surface with octadecyl and methyl ligands, a rod shaped monolith was clad with polymer, and was equipped to an LC apparatus. The separation factors for alkylbenzens of the monolithic column was almost the same as that of conventional packed beads column, however, the applied pressure for the same sample flow rate was reduced to 1/2 to 1/3 of conventional one.