Real-time measurement of dimensional swelling in proton-conductive membranes for fuel cells

Real-time dimensional swelling measurements of proton-conductive membranes are reported. Nafion® (IEC = 0.91 meq g-1), a rubbery polymer, and sulfonated Radel® (IEC = 1.95 meq g-1), a stiffer polymer, were swelled by controlled transitions in relative humidity. The membranes' dynamic swelling behaviors were analyzed using two techniques. First, membranes were made optically reflective, and the macroscopic dimensional change was analyzed directly through time-resolved image analysis. Second, the volumetric swelling of membranes containing microspheres were cast and interrogated using Static Light Scattering (SLS), wherein changes in scattered light intensity correlated with the expected volumetric change during relative humidity steps. In macroscopic visualization, both maximum swelling and rate of swelling were found to be lower in sulfonated Radel, which may be attributed to this polymer's stiffer chain structure compared to Nafion®. In SLS, averaged scattered intensity curves for Nafion® showed similar shapes to those from the macroscopic visualization.