Spectroscopic Studies of the Diffusion of Water and Ammonia in Polyimide and Polyimide-Silica Hybrids

Mass transport of low molecular wight penetrants in polyimide and polyimide/silica hybrids has been investigated using time-resolved FTIR spectroscopy and gravimetric analysis. In particular, transporrt of reacting (ammonia) and non-reacting (water) penetrants has been studied as a function of penetrant concentration, evidencing peculiar features related to the presence of the inorganic phase in the hybrid systems. For the case of water, diffusivity and sorption equilibrium have been evaluated in an activity range between 0.1 and 0.75. Free water as well as molecular aggregates have been detected in both systems. In the case of ammonia, its reactivity with polyimide has been directly observed, and the reaction mechanism elucidated. Furthermore, it has been possible to discriminate diffusion and reaction phenomena due to the different time scales of the two processes.