Kinetics of the sol/gel transition

A 3-component gel containing two polymerizing species has been made by mixing tetraethyl orthosilicate and potassium methoxide in propanol, aging the solution and adding aluminum butoxide and 1 4 theoretical water for hydrolysis. Upon addition of the water and gentle heating, the solution gels uniformly. Experience forming gels indicates that it is preferrable to mix components without water, encouraging polymerization before adding a fast hydrolyzing component or the water for hydrolysis. This process can be carried out essentially at room temperature without adjustment of the pH. The kinetics of the sol/gel transition have been monitored using gas chromatography which records a decrease in alcohol fraction during polymerization, and using titration which records water absorption during hydrolyzation. Once the sol/gel transition is reached, the result is a monolithic gel which continues to polymerize without additional water.