Liquid Ion Exchange Membranes of Extreme Ionic Selectivity and High Transmissivity

Abstract

Liquid, “oil,” membranes in electrolytic systems have been extensively studied, particularly their electromotive behaviour. Nernst and Riesenfeld [1] considered concentration cells, c₁ A⁺L^- | Membrane |c₂ A⁺L^-, in which the electrolyte concentrations within the membrane phase at the phase boundaries are c₁ • k and c₂ • k, where k is the distribution coefficient. The two phase boundary potentials are identical in magnitude and opposite in signs. Thus, the effective electromotive force of the cell is the diffusion potential c₁ • k||c₂ • k within the liquid membrane. The ionic selectivities of such membranes, the ratio of their transmissivities for the anions over that for cations or vice versa, are computed from the concentration potentials. The latter are ordinarily low because the mobilities of most ions differ only within a limited range; correspondingly, the ionic selectivities of such membranes are rather limited.