Silica gel formation followed by dynamic shear experiments

The formation of silica gel from tetraethoxysilane (TES) in a two-step sol-gel process was followed with dynamic viscoelasticity measurements. Mixtures of TES and ethanol were first hydrolyzed with small amounts of an HCl solution, followed by an addition of water containing NH 4OH. With a higher extent of hydrolysis in the first step, gelation started later, but once started, the elasticity increased more rapidly. These non-destructive in situ measurements proved to supply useful information about gel formation.