Diffusion of water and ammonia through Polyimide-Silica bicontinuous nanocomposites: Interactions and reactions

The diffusion of low mol. wt. penetrants through films of a PMDA-ODA polyimide and a corresponding polyimide-silica bicontinuous nanocomposite (org.-inorg. hybrid) was monitored using time-resolved FTIR spectroscopy and gravimetric anal. A reacting and a non-reacting penetrant, ammonia and water vapor, were used in the study in order to evaluate their relative interactions with the components of the polyimide-silica hybrid from sorption and diffusion measurements. In the expts. with water vapors the sorption equil. was measured with activity levels varying from 0.1 to 0.75. The state of water mols. was examd. on the basis of a simplified H-bonding assocn. model. From the expts. using ammonia as the penetrant, it was possible to sep. the phys. diffusion component from the reaction-detd. transport rate by using different sample thickness and penetrant pressure. A remarkable catalytic effect of the silica phase on the reaction of ammonia with the polyimide was obsd.