Proton transport in polyacrylamide based hydrogels doped with H3PO4 or H2SO4

Protonic transport in polyacrylamide hydrogels doped with H3PO4 or H2SO4 has been studied using impedance spectroscopy, Fourier transform infra-red (FTi.r.) and differential scanning calorimetry (d.s.c.) techniques. These hydrogels exhibit room temperature conductivities greater than 10(-2) S cm(-1); these increase with temperature to 10(-1) S cm(-1) at 100 degrees C. D.s.c. experiments show that H3PC4 doped hydrogels do not undergo any first-order transitions up to 100 degrees C whereas hydrogels doped with H2SO4 decompose at temperatures higher than 70 degrees C. It is shown from conductivity and FTi.r. studies that the concentration of acids and the concentration of water influence the proton transport mechanisms. Long-time conductivity studies performed at temperatures between 70 and 100 degrees C indicate 'drying' of hydrogels, which results in a decrease in conductivity; conductivities remain stable below 70 degrees C. (C) 1997 Elsevier Science Ltd.