O-17-NMR of sol-gel processes of TEOS and TMOS

Water consumption and formation in the acid catalyzed sol-gel processing of TEOS and TMOS can be followed using O-17-NMR. By using O-17-enriched water , insight into the hydrolysis and condensation in the acid step of the sol- gel process can be obtained. It is found that, after initially strong consu mption of water due to hydrolysis, a steady state water concentration resul ts. This amount of water increases upon dilution of the reaction mixture wi th alcohol. For a hydrolyzed TMOS-methanol-water system lower water content s are found than in a comparable TEOS-ethanol system. Addition of ethanol t o a hydrolyzed TMOS methanol system enhances the condensation and a higher water concentration is found.