A New Model of Counterion Condensation in Polyelectrolyte Solutions I. Comparison with Other Condensation Theories and Experimental Data on Counterion Activity Coefficients

Abstract

A new model of counterion condensation (Intermediate Model, IMM) is proposed as a modification of our corrected previous model (CPM). The theoretical predictions of IMM and CPM for the degree of condensation, θ, and the counterion activity coefficient, γ, are compared with those of Manning and Iwasa et al. It is found that γ’s in the absence of added salts estimated by IMM and CPM for infinitely long polyions are hardly dependent on the polymer concentration, Cp, while those for polyions with finite length increase with decreasing Cp. It is the latter that is experimentally observed. This fact indicates that polymer models, in which end effects are considered, should be employed to treat dependence of the condensation phenomena on the ionic strength.