Elucidating the relationship between states of water and ion transport properties in hydrated polymers

Ions transport properties in hydrated polymers is usually correlated with the amount of water assuming that all water contributes equally. Herein, we demonstrate that water in polymers exists in three states (non-freezable, intermediate, and free water), and the different states of water exert different impacts on polymer properties including glass transition temperature and ion sorption and diffusion. We synthesized four systematic series of polymer networks including neutral, zwitterionic, cation exchange, and anion exchange polymers. The amounts of water in different states in the hydrated polymers were determined using Differential Scanning Calorimetry (DSC), and their dependence on the polymer composition is investigated. The glass transition temperature of the hydrated polymers is satisfactorily correlated with the non-freezable water using the Gordon-Taylor equation. The salt solubility is correlated with the combined free and intermediate water, and the salt diffusivity is satisfactorily correlated with the total water using the modified Yasuda model.