THERMAL MEMBRANE-POTENTIAL ACROSS ANION-EXCHANGE MEMBRANES WITH DIFFERENT BENZYLTRIALKYLAMMONIUM GROUPS

The thermal membrane potentials were measured across poly(styrene)-bas ed copolymer anion-exchange membranes with 4.5 and 8% divinylbenzene h aving anion-exchange groups with different hydrophobicity for various electrolyte solutions. Linear relationships between the membrane poten tial (Delta psi) and the temperature difference (Delta T) or the logar ithmic temperature difference (Delta In T) were observed when the aver age 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(+/-) decrease d 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, t hermo-osmosis, and electro-osmosis. For hydrophilic IO3- form membrane s having relatively high water content, the water term (Delta psi/Delt a T)(0) is predominant in Delta psi/Delta T. The equation derived from a set of entropy and coupled absolute temperature difference was a go od approximation in the range of small temperature differences. (C) 19 98 Elsevier Science B.V. All rights reserved.