Effect of the inclusion of a water soluble high molecular weight oligomer on the surface characteristics of silica gel

Abstract

The surface characteristics of pure and polyglycol 4000 containing silica gels were investigated by nitrogen adsorption at − 195°C and water adsorption at 35°C. The addition of polyglycol 4000 during the precipitation of silica gel led to a remarkable increase in the surface area as well as the pore volume and on the other hand a sharp drop in c-BET constant. Thermal treatment led to a variation in the surface characteristics of both pure and polyglycol containing silica gels, but in different ways. Inclusion of polyglycol 4000 led to a retardation of the dehydroxylation process that occurs at elevated temperature. The decrease in surface area at 400°C was much higher in polyglycol 4000 containing silica gel than in the pure simple, an effect which correlated with shrinkage of the polymer at high temperature. Slight increase in surface area at 500°C may be attributed to the phase change from β to α form. For the high content polyglycol sample the phase change effect was counteracted by the shrinkage of the polyglycol. Water vapor adsoprtion indicated that polyglycol 4000 containing silica gel was more lyophobic in character than the pure gel at all temperatures except at 200°C.