Polyimide-silica composite materials: How does silica influence their microstructure and gas permeation properties?

Composite polyimide-silica materials have been synthesized via the sol-gel process and their gas transport properties studied. Structural characteriza tions have been performed showing that materials prepared with large concen tration of silicon alkoxyde are composites made of silica particles embedde d in the polyimide matrix while low-silicon alkoxyde concentration induces homogeneous materials. X-ray diffraction shows that the presence of silicon species induces modifications in the microstructure of the polyimide chain s. These modifications have been confirmed by a shift of the glass transiti on temperature and density variations. Influence of the temperature and sil icon species on the gas transport have been studied using various gases (ni trogen, oxygen, carbon dioxide, and methane) showing that gas permeation co efficients increase with the silicon species proportion. CO2 sorption measu rements have been performed at various temperatures and the results have be en analyzed in terms of the dual sorption theory. Activation energies have been calculated for the permeation and sorption mechanisms. These results s how that silicon species contributes to the overall permeability.