Enthalpy of Interaction of Lithium Nafion Membrane with Aqueous Solutions of Alcohols and Polar Aprotic Solvents

The degree of swelling of the lithium form of the perfluorosulfonic acid membrane Nafion in alcohols (ethanol, 2-propanol), water-alcohol mixtures, and highly polar aprotic solvents (N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP)) was studied, as well as the thermodynamics of membrane-solvent interaction using microcalorimetry. It was shown that the equilibrium swelling degree of the membrane correlates with the donor number of the solvent and the enthalpy of polymer swelling. The enthalpy of membrane swelling in all studied solvents is negative, indicating polymer solvation. Concentration dependences of the swelling and mixing enthalpies in DMF and NMP were studied in greater detail. The negative values of the swelling enthalpy across the entire concentration range of the solvents indicate good thermodynamic compatibility of the membrane with the solvent and highlight the advantage of using these solvents to produce Nafion dispersions due to their strong solvating properties.