Investigation on the structure-electrical property relationship of hydrolyzed poly(vinyl alcohol) membranes

Abstract

This investigation explored the effects of the pre-treatment temperature on the molecular conformations and electrical performance of poly(vinyl alcohol) (PVOH) membranes. The structure and properties of the membranes were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Raman scattering (RS) and impedance measurements (IE). Water molecules absorbed by the PVOH membranes, which decreased in quantity as the temperature increased caused drastic change to be observed in the relative band intensities of the OH and CH$_2$ bonds with respect to the C-C bonds. The observations for the hydrated PVOH were correlated with the proton transport behavior, which were inferred from conductivity relaxation measurements over various temperature regions and were dependent on the water content in the membrane. The results were corroborated by DSC and TGA. For example, the temperature dependence of the conductivity relaxation frequency, $\omega_{\text{max}}$, followed different Arrhenius-type thermally activated processes at low and high temperatures. The corresponding activation energies in the low and high temperature regions were: 1.42$\pm$0.02 and 0.23$\pm$0.02~eV, respectively. In addition, the selected fitting temperature regions and activation energies for the $\omega_{\text{max}}$ data were equivalent (within experimental error) to the values for the dc-conductivity, $\sigma_0$(T). This result indicates that the mechanisms for long range ion displacement (dc conductivity) and ion-ion or ion-polymer chain correlations are identical, (i.e., an ion-hoping occurred in the various hydrated phases of PVOH).