Thermal conductivity and modification of silica aerogels prepared with polymeric precursors

Abstract

Modified silica aerogels were prepared with polyethoxydisiloxanes (E-40) followed by silylation of alcogels and ethanol supercritical drying. Trimethylchlorosilane (TMCS) and dimethyldimethoxysilane (DMMOS) were used as the silylation agents. Transmission electron microscopy (TEM) and nitrogen sorption techniques were used to characterise the modified and unmodified silica aerogels. The existence of the methyl groups on the internal surface of aerogels was observed with an infrared and 29 Si magic-angle spinning nuclear magnetic resonance spectrometer (MAS-NMR). The thermal conductivities of silica aerogels were measured as a function of air pressure and mixture (air and water vapour) pressure, respectively. The results were discussed by considering the adsorption of water vapour by the silica aerogels.