High-Pressure Electrical Conductivity and NMR Studies in Variable Equivalent Weight NAFION Membranes

Abstract

Measurements of the electrical conductivity and proton and fluorine-19 NMR spin−lattice relaxation times (T1) in acid form NAFION 105, 117, and 120 conditioned at various levels of relative humidity have been carried out. Complex impedance studies were made along the plane of the polymer film at frequencies from 10 to 108 Hz at room temperature and pressures up to 0.3 GPa. The NMR measurements were made at room temperature and pressures up to 0.25 GPa. Both types of measurement were also carried out on various concentrations of sulfuric acid in water. The electrical conductivity decreases with increasing pressure for low water content acid solutions and low water content NAFION samples. This behavior (positive activation volumes) is that expected for “normal” liquids and for ions in polymers where the motion of the ions is determined by the host matrix. However, for high water contents, the reverse is true. The electrical conductivity increases with increasing pressure which gives rise to a negative activ...