The Donnan law and its application to ion exchanger polymers

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Abstract
A new technique of measuring the electrolyte uptake from dilute solutions by ion exchanger polymers has been developed, which permits measurements at solution concentrations as low as 10$^{-4}$ M. The results show that the Donnan equilibrium relation, which at low concentrations predicts a co-ion distribution coefficient proportional to the solution concentration, is not obeyed. Instead it is shown that the distribution coefficient is proportional over a very wide range to a low power of the external counter-ion concentration. Measurements of the diffusion coefficients in the exchanger phase show an abnormally high dependence on concentration. The conclusion is drawn that these phenomena are due to the fact that even the `homogeneous' exchanger polymers are not uniform and thus cannot be treated as a single phase.