Investigation of the interaction of a polyelectrolyte with low molecular weight electrolytes containing nonidentical counterions by differential refractometry

If the counterion of a polyelectrolyte is not identical with any of the ions of a low molecular weight electrolyte added to the solution, the system may be regarded as a four‐component system. Relations for the refractive index increments have been derived which allow the determination of the coefficient of selective sorption of the added electrolyte from the refractive index increments of the components independent of the original counterion of the polyelectrolyte. Equilibrium dialysis and differential refractometry were used to study the interaction of KCl, KBr and NaI with poly[‐1(2‐hydroxyethyl)pyridiniumbenzenesulfonate methacrylate] or with an analogous polymer containing a toluenesulfonate counterion in aqueous solutions. The coefficient of selective sorption increases in the series Cl− < Br− < I− from strongly negative to strongly positive values; the specific interaction of these counterions with the macroion increases in the same order.