Electrical conductivity of cation-exchange membranes in the hydrogen ion form

Abstract

Measurements are reported of the conductivities of a number of different cation-exchange membranes in the hydrogen-ion form. The membranes were equilibrated both with water and with sulphuric acid solutions of concentrations up to 6N, and the amounts of water and acid absorbed were also measured. Some of the membranes used were found to undergo an irreversible expansion on heating. When equilibrated with water, equivalent conductivities of the homogeneous- type membranes could be fitted by the equation Δ = A(1- Vp), where Vp is the volume fraction of polymer and A is a constant whose value depends on the concentration of ion-exchange groups but which is little affected by the nature of the membrane. In the presence of acid the conductivity changes depend markedly on the presence of voids. This behaviour can be well described in terms of the model of Sauer, Southwick, Spiegler, and Wyllie, which treats the membrane as an assembly of solid resin and continuous and discontinuous voids. Evaluation of these results in terms of this model enables estimates to be made of the extent and nature of the voids. On adding acid to a membrane there is at first a rapid rise in apparent counter-ion mobility, followed by a fall at higher acid concentrations. The initial rise in apparent mobility is attributed to the entry of acid into discontinuous voids.