Mechanical properties and influence of straining on ion conductivity of perfluorosulfonic acid Nafion®-type membranes depending on water uptake

Abstract

The results of an investigation of the mechanical properties of a perfluorosulfonic acid MF-4SC membrane (Russian analogue of Nafion®) in the H+ and Na+ ion forms at different relative humidity (RH) values ranging from 0% to 95% are presented in this article. The dependences of Young׳s modulus and the proportional limit stress on RH reach a maximum at RH=32–58%. The influence of the strain on the ionic conductivity measured in parallel and perpendicular directions to the strain is studied. The conductivity of membranes strained within the region of irreversible deformation is lower than the conductivity of the initial membrane but relaxes and increases up to the values of the initial membrane 2h after the straining. The conductivity of broken membranes maintained at RH=9% is higher than the conductivity of the initial membranes under similar conditions. Anisotropy is observed in the ion transport of broken membranes. At RH>32%, the conductivity measured parallel to the straining is higher than that measured perpendicular to the straining, while at RH≤32%, the conductivity is higher in the perpendicular direction. Explanations of the processes occurring during the straining and following relaxation of the membranes are proposed.