A new approach to ion exchange polymers

The observed abnormal behaviour of the electrolyte uptake in ion exchangers (see preceding paper by Glueckauf & Watts) is interpreted quantitatively on the basis of a widespread non-uniformity of distribution of the counter-ions. In the case fully treated in this paper, i.e. for an exchanger of mean molality of 4·17, the range of counter-ion concentrations is shown to extend from about 15 molal to 10-4 molal. This non-uniformity must have significant effects on the variation of the ion exchange separation factor at different mol-fractions in the exchanger phase. It explains qualitatively the observed fact, that the separation factor is usually larger when the more strongly sorbed ion is present at low mol-fractions, and that this effect increases both with the mean molality of the exchanger, and with the magnitude of the separation factor. The wide non-uniformity also explains the observed variation of the diffusion coefficient of imbibed electrolyte with concentration. A new quantitative treatment is introduced for diffusion through widely non-uniform media. Full agreement between theory and experiment is obtained at high uptake concentrations. At low uptake concentrations, two curves are obtained from the theory, according to whether the low concentration regions in the exchanger are considered as ‘continuous’ or ‘disperse’. The observed data lying between these two calculated curves suggest a considerable ‘continuity’ for the low concentration regions. They indicate the existence of a ‘continuous’ network of submicroscopic aqueous fissures or channels of about 70 Å width, widening occasionally to as much as 2000 Å. The resulting electrical double layer effects in these fissures explain the wide continuous variation of counter-ion concentrations.