Reactions of (CH3O)4Si and C16H33Si(OCH3)3 at various mole ratios were performed in methanol using base and acid catalysis. Sol-gel materials were formed that have low surface areas (∼10 m2/g). Subsequent supercritical drying using CO2 at 40 °C produced materials that are very different than traditional aerogels, with surface areas around the same values as the corresponding sol-gels, as well as no detectable meso-pore features. In some cases, the aerogels even melted upon heating. Spectroscopic characterization, using IR, 29Si and 13C NMR revealed normal Si-O substitution as well as incorporation of the carbon chain into the Si framework.
Heating of the stable forms of the materials in air at different temperatures yielded, depending upon oxidation conditions, several materials with much higher surface areas, typical of aerogels. Pore size distribution measurements revealed meso-pore features with a narrow distribution around 35Å. Spectroscopic characterization revealed the disappearance of the R-Si substitution and the appearance of an oxidized intermediate.
This paper will describe the chemistry and characterization of these unusual sol-gels, aerogels, and oxidation products, as well as potential applications.