Nafion β-Relaxation Dependence on Temperature and Relative Humidity Studied by Dielectric Spectroscopy

Abstract

Nafion β-relaxation was studied by detailed dielectric spectroscopy measurements carried out over a wide range of both temperature and relative humidity. Both cast and extruded Nafion were compared in the H+, Na+, and Cs+ forms to evaluate contributions arising from membrane morphology and ionic interactions. The combined data indicated that β-relaxation is related to the motion of the polymer side chains. The shift to lower frequencies of the β-relaxation was shown to be more pronounced for samples containing high water content at temperatures above the α-relaxation, evidencing that the electrostatic repulsions between bare sulfonic groups reduce the side chain mobility. An abrupt change of relaxation time was observed at relative humidity > 60% and associated with a change of morphology of the ionomer from an inverted micellar structure to a rodlike network.