Abstract

Silica gels were presented from alcoholic solutions of tetraethylorthosilicate (TEOS) using a two-step hydrolysis process; small angle X-ray scattering (SAXS), gas-liquid chromatography, and 1H NMR spectroscopy were employed to study their formation. The first step (1 mol. H2O/mol. TEOS with HCl catalyst) resulted in a rather wide species distribution comprised of hydrolyzed and unhydrolyzed monomers, dimers, and chains. The second step (additional water plus acid or base) resulted in completely hydrolyzed polymers in the acid system which apparently were highly overlapped prior to gelation. In the base system, hydrolysis was incomplete due to unhydrolyzed monomer and the resulting polymers were more highly condensed (or collapsed) and discrete compared to the acid system. The formation of colloidal silica was not obseerved in either case.