Influence of Donnan and dielectric exclusion on ion sorption in sulfonated polysulfones

The Donnan – Manning model accurately describes the thermodynamic properties (e.g., ion sorption) of many charged polymers equilibrated with aqueous electrolytes, such as the commercial ion exchange membranes CR61 and Nafion. It less accurately describes the ion sorption properties of sulfonated polysulfone, which is a promising desalination membrane polymer. One possible explanation is that other ionic interactions that are not included in the Donnan – Manning model, e.g., dielectric exclusion (or ion solvation effects) that can be described via the Born model, may have a significant influence on ion sorption in sulfonated polysulfones. We developed a model to account for the influence of both Donnan – Manning and dielectric exclusion factors on ion sorption properties and applied it to sulfonated polysulfones and Nafion. This Donnan – Manning – Born model described the ion sorption properties of sulfonated polysulfones more accurately than the Donnan – Manning model alone. The Donnan – Manning – Born model also predicted ion sorption properties in Nafion with improved accuracy relative to Donnan – Manning predictions, but the improvement was less significant than in the sulfonated polysulfone case. These results provide an approach for quantifying the influence of dielectric exclusion on ion sorption in charged polymers and could be particularly important for materials where dielectric exclusion is relevant.