DETERMINATION OF WATER DIFFUSION-COEFFICIENTS IN PERFLUOROSULFONATE IONOMERIC MEMBRANES

Pulsed field gradient spin-echo H-1 NMR measurements of H-1 intradiffusion coefficients at 30-degrees-C in hydrated Nafion membranes are reported. The dependence of the H-1 self-diffusion coefficient on membrane water content was a central part of this investigation. H-1 diffusion coefficients ranged from 0.6 x 10(-6) to 5.8 x 10(-6) cm2/s for the range of membrane water content 2-14 water molecules per sulfonate. The membrane water content was controlled by isopiestic equilibration of the membrane sample with water vapor above aqueous LiCl solutions of well-defined water activities. The dependence of membrane water content on water activity enables us to estimate "chemical diffusion coefficients" from the intradiffusion coefficients measured by NMR.