ASYMMETRIC [NAFION(R)] [SILICON OXIDE] HYBRID MEMBRANES VIA THE IN-SITU SOL-GEL REACTION FOR TETRAETHOXYSILANE/

Asymmetric silicon oxide composition profiles along a direction perpen dicular to the plane of Nafion(R) sulfonate films were created via in situ sol-gel reactions for one-sided tetraethoxysilane permeation, as verified by EDAX/ESEM. For K+ form membranes, we propose the existence of an IR spectral signature of molecular branches in addition to thos e characteristic of linear and cyclic fragments in the silicon oxide p hase. The molecular structure of the silicon oxide phase is more inter connected than linear in K+ form membranes. For H+ form membranes, the re appears to be an increasing degree of molecular linearity within th e silicon oxide phase with increasing uptake. IF spectra indicate that molecular connectivity on the permeated side is lower, on the average , than that on the nonpermeated side. The inverse relationship between gas permeability and upstream pressure in steady-state helium gas tra nsmission experiments suggests the dual-mode sorption of gases, which is in harmony with the multiphasic nature of these membranes. (C) 1996 John Wiley & Sons, Inc.