Published online by Cambridge University Press: 21 February 2011
Capillary stresses during drying that result from the contact angle of aliquid solvent to a gel, surface tension, and pore size have an immenseeffect on the dried gel. The extent to which the gel shrinks is a balancebetween the capillary stress and the solid matrix strength. The dynamiccontact angles and surface tensions of various solvents commonly employed insol-gel processing on silica gels of various surface chemistries have beenevaluated. A thin, dense coating of silica gel was formed by dip coating astandard glass slide in an acid catalyzed silica sol and drying. Some of thesample surfaces were organically modified. Dynamic contact angles weredetermined using a modified Wilhelmy plate technique. Solvent surfacetensions were determined using the De Nouy ring technique. The bulk modulusof wet gels were determined with a three point bend experiment. We havefound that contrary to previous investigators, who attributed different bulkdensities obtained after drying from various alcohols to contact anglesvariations, gel shrinkage during drying is actually due to slightlydifferent surface tensions and degrees of depolymerization of the gelnetwork.