SILICA-GELS MADE BY BICONTINUOUS MICROEMULSION POLYMERIZATION

Microporous silica gels can be made by polymerizing partially hydrolyzed tetramethoxysilane sols present in the aqueous phase of bicontinuous microemulsions stabilized with didodecyldimethylammonium bromide. Then vacuum-dried, the gels made in microemulsions have about twice the specific surface area of conventional vacuum-dried silica gets. They have 70% of the specific area of supercritically dried gels. Small-angle X-ray scattering measurements in these gels show two characteristic sizes. One size, around 24 Angstrom, in the original microemulsion is retained during polymerization, but lost when the detergent is extracted. The second size grows with the square root of time during the polymerization, suggesting diffusion-controlled gelation.