Colligative properties of polyelectrolyte solutions in excess of salt

Abstract

Abstract This work treats the equilibrium properties of polyelectrolyte solutions containing an excess of low molecular salt. In this case the simple rule of additivity, dealt with previously, fails to describe the experimental results. A detailed treatment, based on an approximate solution of the Poisson‐Boltzmann equation, was therefore undertaken. The calculation is based on a subdivision of the electrostatic potential into two parts corresponding to two regions: ( 1 ) an inner region in the close neighborhood of the polyion, free of coions and described by the Poisson‐Boltzmann equation in the salt‐free case, and ( 2 ) an outer region screened off from the central macroion and adequately treated by a Debyean approximation. An analytical solution for the electrostatic potential was obtained and used for the theoretical description of potentiometric behavior, Donnan distribution of salt, and Donnan osmotic pressure. The predicted values compare favorably with the measured results in a wide range of experimental conditions.