Silylation of polydiethoxysiloxane derived silica aerogels

Silica aerogels were prepared with polydiethoxysiloxane (PDEOS) followed by silylation of the alcogels and supercritical drying from ethanol. Trimethylchlorosilane (TMCS) and dimethyldimethoxysilane (DMMOS) were used as the silylation agents. Transmission electron microscopy (TEM) and nitrogen sorption techniques were used to characterize the modified and unmodified silica aerogels. The existence of the methyl groups on the internal surface of aerogels was observed using an infrared and a 29Si magic angle spinning nuclear magnetic resonance (MAS–NMR) spectrometer. The results indicate that the condensation degree of PDEOS derived silica aerogels is higher than that of TMOS and TEOS derived aerogels. The silylation process removes Si–OH surface groups by promoting silica polycondensation, resulting in a decrease of pore size and an increase of both particle size and specific surface area of the aerogels.