A two-step silica sol-gel process investigated with static and dynamic light-scattering measurements

The hydrolysis-condensation reactions in mixtures of tetraethoxysilane, ethanol and water were followed in the basic step of a two-step silica sol-gel process with dynamic and static light-scattering techniques. The radii of the particles formed were found to be about 1.5 nm and in agreement with the results found with specific surface area measurements on the corresponding dried silica gels. The relatively high scattering found for mixtures having incomplete hydrolysis in the acid step was ascribed to the formation of large particles caused by prolonged hydrolysis-condensation in the basic step. The decreased light transmission as a function of the decreasing density of dried silica gels was assigned to Rayleigh scattering by pores.