Thermodynamics of pore wetting and swelling in Nafion

A model for the wetting and swelling of pores with water within a Nafion membrane, based on minimizing all contributions to the total free energy, is developed. We find that equilibrium state depends on entropic mixing forces and energetic surface forces. The wetting of the pore relies on the entropic forces exceeding the energetic forces. If the pore fills with liquid it will swell until balanced by the energy of the deforming membrane. Several factors including pressure relative to saturation and the phase which bounds the membrane are shown to dramatically affect the final equilibrium state of the system.