Dielectric properties of hydrated Nafion-(SO3K) membranes:: thermally stimulated depolarization currents

Dielectric studies have been carried out on hydrated perfluorosulfonate polymer membranes in potassium salt form, 1190 g equivalent(-1) by means of thermally stimulated depolarization current (TSDC) techniques in the temperature range 77-300K. Three dispersions I-III, are observed in a TSDC thermogram, and their positions depend upon the water content. We employ thermal sampling (TS) to analyse the three relaxation process experimentally, into approximately single responses and to determine the spectra of activation energy, E(T), on a sample with a water content of 0.9 H2O/SO3K. Dispersion I is analogous to the gamma-relaxation mechanism, which was observed in mechanical relaxation studies, with an activation energy between 0.55 and 0.68 eV. Measurements with different electrode configuration reveal different aspects of the dynamics of the relaxation mechanism and allow distinction between dipolar and interfacial polarization contributions of Dispersion II. Dispersion II is analogous to the beta-relaxation mechanism that was observed in mechanical relaxation studies on hydrated membranes. Dispersion III may be due to a phase or structural change of the material in this temperature range. However, a contribution to this peak from electrochemical effects at the electrodes cannot be excluded. (C) 1998 Chapman & Hall.