CHARACTERIZATION OF PERFLUOROSULFONIC ACID MEMBRANES BY CONDUCTIVITY MEASUREMENTS AND SMALL-ANGLE X-RAY-SCATTERING

Three perfluorosulfonic acid membranes, Nafion 120, Nafion 117 and Dow , pretreated in water at 100-degrees-C were characterized by conductiv ity measurements in the temperature range of 20-90-degrees-C and by Sm all-Angle X-Ray Scattering (SAXS) at room temperature. The results dem onstrate that conductivity is determined by the apparent proton equiva lent conductivity and not the proton volume concentration. The apparen t equivalent conductivities increase in the sequence Nafion 120 < Nafi on 117 < Dow. SAXS reveals the same average cluster size of 5.3 nm for all three membranes but different cluster densities increasing in the sequence: Nafion 120 < Nafion 117 < Dow. Therefore, the proton equiva lent conductivity is determined by the cluster density with the polyme r network.