Investigation of the transport properties of a quaternary ammonium anion exchange membrane. Part 2.—Application of irreversible thermodynamics to the iodide form

Abstract

A detailed study of the equlibrium and transport properties of the iodide form of a strong base quaternary ammonium anion exchange membrane has been completed. The selectivity coefficients K^I_Cl are large and the free energy for exchange some –6 kJ mol^–1, suggesting strong binding of iodide to fixed charge. All transport measurements were made in 0.1 mol dm^–3 sodium iodide and a complete irreversible thermodynamic analysis of the isothermal transport processes at 298.15 K completed. The iodide membrane contains very little water, only 3.9 mol/equivalent of exchangeable ion and is also effectively free of invading salt. The major difference, between this membrane in the iodide form and earlier chloride studies, lies in the extremely large friction between iodide and matrix fixed charge. This kinetic friction dominates all ionic transport and accounts for 98% of the observed electrical resistance of the membrane. Frictional interactions between membrane ions and water and between water and isotopic water are normal. Evidence that linear phenomenological equations may only apply under very small electrical forces is presented in electro-osmotic studies.