Kinetics of the Early Stages of the Sol-Gel Process: III. Evolution of Silica Associates

摘要

A kinetic scheme is proposed for the processes of hydrolysis of alkoxysilanes and polycondensation of the hydrolysis products represented as monomers, dimers, trimers, oligomers, and polymers. A kinetic model that makes it possible to evaluate the weight fractions of silica associates at different instants of time after the beginning of the hydrolysis and to determine the kinetic characteristics of these processes is constructed. The evolution of silica associates at different pH values and dilutions at the early stages of the hydrolytic polycondensation of silicon alkoxides is analyzed. It is noted that the structuring of silica in the case of tetraethoxysilane differs from the structuring for tetramethoxysilane.