Thermal membrane potential across anion-exchange membranes with different benzyltrialkylammonium groups

The thermal membrane potentials were measured across poly(styrene)-based copolymer anion-exchange membranes with 4.5 and 8% divinylbenzene having anion-exchange groups with different hydrophobicity for various electrolyte solutions. Linear relationships between the membrane potential (Delta psi) and the temperature difference (Delta T) or the logarithmic temperature difference (Delta In T) were observed when the average temperature T-av was kept at 308.2 K and Delta T varied from - 10 to + 10 K. The values of Delta psi/Delta T against log a(+/-) decreased with increasing hydrophobicity of the ion-exchange groups. The mean transported entropy of the counterions (s) over bar(-) in the membrane was estimated by combining data for the thermal membrane potential, thermo-osmosis, and electro-osmosis. For hydrophilic IO3- form membranes having relatively high water content, the water term (Delta psi/Delta T)(0) is predominant in Delta psi/Delta T. The equation derived from a set of entropy and coupled absolute temperature difference was a good approximation in the range of small temperature differences. (C) 1998 Elsevier Science B.V. All rights reserved.