Acidic Sol−Gel Polymerization of TEOS: Effect of Solution Composition on Cyclization and Bimolecular Condensation Rates

摘要: For batch sol−gel polymerization of TEOS in acidic ethanol solutions, we report kinetic trends over a wide range initial solution compositions that yield homogeneous gels. We find these systems the prevalence extensive nonrandom cyclization composition range. unambiguously monitor formation various well-defined silicate oligomers early reaction to quantify competing processes and bimolecular condensation. introduce new model is substantially modified from previously used random branching models order account for reactions. As do previous models, this allows first-shell substitution effects on condensation rate constants, but it does not rely mean field site kinetics. The dimerization constant varies strongly with pH manner consistent mechanism involving ionized intermediates. It also decreases mildly water concentration experienced during reaction. Higher ra...