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, followed by hypercritical drying, using 6 solvents of different chain lengths, 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 catalyst produced transparent but cracked aerogels. While weak acids and their combinations with a weak base were found to produce shrunk and semitransparent (opaque for CH3COOH + NH4OH) aerogels, the best quality transparent, monolithic, low-density and refractive index, and large surface area aerogels were obtained for a combination of weak basic catalysts and solvents of shorter branching and chain lengths. The physical properties of the aerogels were studied by BET analysis, porosity, density, refractive index and optical transmission measurements.