17O-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 17O-NMR. By using 17O-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 consumption of water due to hydrolysis, a steady state water concentration results. This amount of water increases upon dilution of the reaction mixture with alcohol. For a hydrolyzed TMOS-methanol-water system lower water contents are found than in a comparable TEOS-ethanol system. Addition of ethanol to a hydrolyzed TMOS methanol system enhances the condensation and a higher water concentration is found.