CONTROLLING MICROMORPHOLOGY OF SILICA GELS BY UNIDIRECTIONAL FREEZING AND FREEZE DRYING

Unidirectional freezing and freeze drying were applied to a wide variety of silica gel precursors: from hydrosols to thoroughly aged hydrogels. Porous silica gels with 3 kinds of morphologies (lamella, flat fiber and microhoneycomb) were prepared from unidirectional freezing of hydrosols. On the other hand, porous silica gels prepared by unidirectional freezing of hydrogels had 3 kinds of morphologies (microhoneycomb, fiber with polygonal cross-section and powder). The morphologies of silica gels prepared were mapped for the gelation time, the aging time and the delay time determined from dynamic light scattering (DLS) measurements of silica hydrosols. The morphology of silica gel can be controlled by using the proposed map.