EFFECT OF SOLVENTS AND CATALYSTS ON MONOLITHICITY AND PHYSICAL-PROPERTIES OF SILICA AEROGELS

The effect of various solvents and catalysts on the monolithicity and physical properties of silica aerogels is reported. The aerogels were prepared by hydrolysis and polycondensation of tetramethoxysilane, fol lowed by hypercritical drying, using 6 solvents of different chain len gths, and 17 catalysts consisting of strong and weak acids, bases and their mixtures. It was found that solvents of longer chain lengths and strong basic catalysts resulted in semitransparent to opaque aerogels , whereas strong acids and their combinations with a weak basic cataly st produced transparent but cracked aerogels. While weak acids and the ir combinations with a weak base were found to produce shrunk and semi transparent (opaque for CH3COOH + NH4OH) aerogels, the best quality tr ansparent, monolithic, low-density and refractive index, and large sur face area aerogels were obtained for a combination of weak basic catal ysts and solvents of shorter branching and chain lengths. The physical properties of the aerogels were studied by BET analysis, porosity, de nsity, refractive index and optical transmission measurements.