Water and Ion Transport through the Glass Transition in Polyelectrolyte Complexes

Polyelectrolyte complexes or coacervates, PECs, represent one of the many families of ion-containing polymers proposed or in use for applications requiring mobile ions, including fuel cells, water purification, and rechargeable batteries. Interest in these materials has focused on how ion transport is coupled to, and limited by, polymer dynamics, which slow considerably below the glass transition, Tg. Unlike many other polymer systems, ion conductivity in hydrated PECs remains high above and below Tg. In this work, we investigate the transport of water and ions within a PEC as the polymer host passes through Tg. We find no evidence of a response in the transport of water and small univalent ions, such as Na+ and Cl–, as the hydrated PEC goes through Tg. In contrast, triple-charged ions ferricyanide and ruthenium hexamine experience a second-order change in transport rate at Tg. This response is interpreted to show that these ions engage enough polyelectrolyte repeat units to experience the highly localized cooperative rearrangement thought to be responsible for the glass transition.