A COMPARISON OF THE MICROSTRUCTURAL PROPERTIES OF SILICA AEROGELS AND XEROGELS

Silica aerogels and xerogels have been prepared by the sol-gel polymerization of tetraethylorthosilicate. The sol-gel conditions have been varied by altering the quantities of alcohol solvent and water in the initial sol-gel composition. The effect of changing the size of the alkyl chain of the alcohol solvent has also been investigated. The samples prepared have been examined using nitrogen adsorption analysis, mercury porosimetry and transmission electron microscopy. Macroporous and mesoporous aerogels of surface areas between 200 and 1000 m2/g may be prepared. Macroporosity is favored by a high water content and short alkyl chain length of the solvent alcohol whereas mesoporosity is favored by a low water content, high alcohol content and a branched chain alcohol as solvent. Microporous and mesoporous xerogels of surface areas of 350-1000 m2/g may also be prepared. Microporosity is favored by a high alcohol content and a short-chain alcohol whereas mesoporosity is favored by a high water content and a long-chain alcohol solvent. Hence, changing the sol gel conditions has different effects in the resulting aerogels and xerogels.