Donnan equilibria of simple electrolytes in polyelectrolyte solutions

Abstract

Salt exclusion parameters, Γ[=(m^′_s–m_s)/m_e: where m_e denotes the polyelectrolyte concentration, and m_s and m^′_s represent the salt concentrations of the solutions with and without polyelectrolyte] of NaCl and Na₂SO₄, have been determined for sodium polyacrylate (NaPA) and sodium polystyrene sulfonate (NaPSS) by equilibrium dialysis and a non-equilibrium method based on emf measurement. An empirical equation with a single parameter, k, described the results to a good approximation when k was allowed to increase with m_e. Values of k were identical for NaCl and Na₂SO₄, within the experimental error, for a given polymer, NaPA or NaPSS. This suggests that k is determined by the interaction of the polyelectrolyte with its counterions. At m_e= 0.001 mol kg^–1, values of Γ were close to those given by the limiting law. Values of Γ for NaPSS were generally greater than those for NaPA.