Interpretation of Electrolyte Invasion Data for Ion-exchange Polymers

Abstract

IN recent years two quite independent theories have been developed to account for the observed electrolyte invasion properties of ion-exchange polymers. Scatchard and Freeman¹ suggest that in the application of the Donnan law (1), deviations are best interpreted in terms of the mean activity coefficient of the electrolyte in the exchanger phase, ɣ̄±. where ν_c is the number of co-ions in a molecule of electrolyte; ν_g is the number of counter or gegen ions in a molecule of electrolyte, ν = ν_c + v_g; M is the observed counter-ion concentration; m, the concentration of external electrolyte; m̄, the concentration of imbibed electrolyte; k, a constant; ɣ̄ ± and γ ± are the mean internal and external activity coefficients of the electrolyte, respectively. In accordance with the theory of specific ion interactions², an expression has been derived (2), in which a and b are constants, to account for variations in ɣ̄± for ion-exchangers based on styrene-divinylbenzene copolymers. This relationship has also been applied to polymethacrylic acid ion-exchangers³. It is assumed in this treatment that any deviations resulting from non-uniformity of the exchanger matrix are either negligible or can be eliminated by a small correction to the observed results.