LOW-DENSITY, MUTUALLY INTERPENETRATING ORGANIC-INORGANIC COMPOSITE-MATERIALS VIA SUPERCRITICAL DRYING TECHNIQUES

Low-density SiO2 aerogels are an interesting class of materials for wh ich commercial applications have been hampered by their brittle mechan ical properties, hygroscopic nature, and sometimes limited transparenc ies. We have been interested in addressing these key problems by devel oping methods of homogeneously incorporating organic polymers within t he SiO2 framework. The formation of low-density organic-inorganic aero gel materials that show improved properties over conventional aerogels is reported. Two approaches are presented, both of which rely on supe rcritical CO2 exchange during the drying process. The first approach i nvolves addition of preformed polymers poly(2-vinylpyridine) (PVP), po ly[methyl methacrylate-co-(3-trimethoxysilyl)propyl methacrylate)] (PM MA-TMSPM), and silanol-terminated poly(dimethylsiloxane) (PDMS) to the sol-gel precursor solutions, while the second approach involves formi ng the organic polymer cross-linked poly(N,N-dimethylacrylamide) (PDMA ) in situ. In both cases bonding of the organic phase to the SiO2 stru cture is important and crosslinking of the organic polymer further imp roves their properties. The mechanical, optical, and hydroscopic prope rties of these materials are reported.