More studies on the PVAl+H3PO2+H2O proton conductor gels

Solid polymer proton conductors made of poly(vinyl alcohol) (PVAl), hypophosphorous acid (H3PO2) and water with conductivities as high as 0.1 S cm(-1) at room temperature were studied by means of differential scanning calorimetry (DSC), X-ray diffraction and thermogravimetry (TG). The DSC curves for membranes with the highest acid concentrations show on heating a very low glass transition temperature (revealing a separate acid/water phase), a cold crystallization after this glass transition, a melting of crystallizes or of the freezing water in the polymer network and a recrystallization above ambient temperatures as the membranes lose water. The X-ray spectra for the raw samples at room temperature indicate that the amorphousness of PVAl complexes increases with the concentration of H3PO2; but its degree of crystallinity increases with the annealing time of samples above room temperature. The TG traces confirm that membranes with the highest acid concentrations have the highest water content and that the maximum rate of water removal is at about 50 degrees C for all samples. (C) 2000 Elsevier Science Ltd. All rights reserved.