Effects of alcohol solvents on formation of the hydrated silica gel

Abstract

Usually, when silica sol is prepared by adding inorganic acid to a diluted sodium silicate solution, a basic substance is added to adjust the pH of the silica sol in order to occur the gelation reaction of the silica sol. However, in this study, it was confirmed that the gelation of the silica sol could occur even when an alcohol is added instead of the basic substance. In order to examine the mechanism of gelation that occurred when alcohol was added to the silica sol, different solvents (protic and aprotic) were added to the silica sol and the gelation time was measured. The results revealed that the gelation occurred due to the tendency of the hydroxyl oxygen in the alcohol to bond to the hydroxyl hydrogen of the water molecules that had already formed a hydration shell around the silica particles. Therefore, it is presumed that the hydration shell was broken by the addition of the alcohol. This, in turn, led to the instantaneous polycondensation between the silica particles, which caused the gelation.