Impact of ionic correlations on the selective transport of salts through polymer membranes

Polymer membranes can be utilized for ionic separation through the incorporation of host-guest interactions. This is achieved via selective binding of the polymeric functional groups with a particular ionic species in a mixture, thereby altering the relative solubility and diffusivity of the ions within the membrane. We employ molecular dynamics simulations to probe the effect of membrane chemistry and feed composition on the diffusivity selectivity of salts in a binary mixture. Furthermore, the diffusivity selectivity for binary mixed salt systems is compared to that obtained from corresponding single salt systems. We utilize the Onsager framework to quantify the impact of ionic correlations on salt transport within the membrane. We show that ionic correlations can lead to significant deviations of salt diffusion from ideality. Our parametric study helps identify the conditions under which ionic correlations become dominant and therefore cannot be neglected during experimental estimation of salt diffusivity. The results from this work will aid in design of polymer membranes with high ion-specific selectivity.