Hydrophobic silica aerogels

Abstract Hydrophobic silica aerogels were produced by the -Si(Me)3 (trimethylsilyl substituent: TMS) modification of alcogels followed by CO2 supercritical drying. The structure of trimethylsilyl modified silica aerogel (TMSA) was the silica matrix produced by hydrolysis and condensation of only tetramethoxysilane (TMOS). TMS was modified on the surface of the silica matrix. TMSA was extremely moisture-resistant. The density, size, and transparency of TMSA samples were maintained after the moisture-resistance test. The moisture-resistance of trimethylsilyl modified silica aerogels (TMSAs) was superior to that of conventional aerogels supercritically dried by the ethanol method. Another feature of TMSA was the small shrinkage during supercritical drying. The shrinkage ratio of TMSA was less than 3% by comparison with about 5% for conventional aerogels. TMSA had the same transparency as conventional aerogels, with a transmittance of 90% at a thickness of 1 cm. The existence of TMS was observed using infrared, 13C nuclear magnetic resonance (NMR) and 29Si NMR.