Structural evolution of water swollen perfluorosulfonated ionomers from dry membrane to solution

The structural evolution of perfluorosulfonated ionomer (PFSI) membranes fr om dry materials to highly swollen membranes and solutions was investigated using mainly small-angle scattering techniques. The small-angle scattering maximum ("ionomer peak") is shown to be observable up to very large water content and shifts continuously toward small-angle as water content increas es. A modification of the swelling process is observed for a water content larger than 50% by volume. This behavior is attributed to an inversion of t he structure from a reverse micellar structure to a connected network of po lymer rod-like particles. The swelling behavior of the membranes was determ ined in different solvents and was analyzed in terms of interfacial energy effects. The conductivity measurements indicate that the structure of the h ighly swollen membrane is close to the one observed for solutions. (C) 2000 Elsevier Science Ltd. All rights reserved.