Studies of Polyelectrolyte Solutions I. Counterion Condensation by Poly(styrene sulfonate)

Abstract

Polyion-counterion interactions of poly(styrene sulfonate) have been studied in the mixed electrolyte systems Pb2+/H+/NO3− and Pb2+/Na+/NO3− at various ionic strengths, I, polyion concentrations, cp, and temperatures, T, utilizing the dialysis equilibrium technique. The degrees of condensation, θ1 and θ2, obtained for the uni- and divalent counterions are compared with those predicted by the two-variable theory of Manning. It is found that the decrease (increase) in θ2 (θ1) observed with increasing ionic strength at fixed Pb2+- and polyion concentration is very well predicted by this theory. The extent of Pb2+-ion binding is largest for the Pb2+/H+ counterion combination, and lowest for the Pb2+/Na+ combination. In both cases the binding of one Pb2+-ion releases close to two univalent counterions. A polyion concentration dependence of θ1 and θ2, on the other hand, could not be found at all. The reason may be, that the ionic strength of 0.01 mol l−1 used is too low. At fixed I, cp and cPb2+, θ1 and θ2 decrease slightly as the temperature increases. According to the two-variable theory, θ1 and θ2 are independent of T. Agreement between theory and experiment can be achieved if bbrut, the brut (rough) average linear charge separation on the polyion, is an increasing function of the temperature.