NMR and IR spectroscopy of silica aerogels with different hydrophobic characteristics

Silica aerogels, prepared by the sol–gel method and dried by the CO2 supercritical method, were produced from tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMS) in different proportions, in order to change the proportions of hydrophilic and hydrophobic surface groups. The aerogel hydrophobic or hydrophilic properties were related to their surface structural characteristics. The relative proportion of Si–OH, Si–OCH3 or Si–CH3 groups present on the aerogel pore surface and its silica network structure were determined by 1H, 29Si and 13C nuclear magnetic resonance (NMR). The results obtained were correlated with the infrared transmission spectra. From these data, a possible description of the mixed hydrophilic–hydrophobic nature of the surface of these materials is proposed.