Counterion dissociation in mixtures of sodium polystyrenesulfonate with different molar masses in aquo-organic media

Abstract

The counterion dissociation of polyelectrolytes is extremely important and pivotal in determining the charge state of polyions and the interaction between polyions and counterions. Polyion charges have been estimated via conductometry using sodium polystyrenesulfonate as a model under various experimental conditions. Analyses of conductance–concentration data have been performed on the basis of the scaling description of the polyelectrolyte configuration. The effective charges on the polystyrenesulfonate chains have been found to depend on the polyelectrolyte concentration, particularly in the low concentration region, and finally reach a plateau as the concentration is subsequently increased. This study also revealed that the degree of counterion condensation is altered appreciably with the composition of the polyelectrolyte mixture, the relative permittivity of the medium and the temperature. The roles of the relative permittivity of the medium, the screening of chain charges, the coiling of polyion chains, and the desolvation of counterions in governing the process of counterion condensation have been critically assessed. An empirical equation to describe the extensive array of the fraction of free counterions obtained in this study has been proposed. This equation has been shown to be very useful, and the absolute average difference or the standard deviation between the experimental and calculated values was always found to be within ±0.01.