Insight into the structural construction of a perfluorosulfonic acid membrane derived from a polymeric dispersion

The effects of the nature of the solvent on the morphology of perfluorosulfonate ionomers in dispersions and the microstructures of the corresponding formed membranes are investigated. The subsequent electrochemical performances of the formed proton exchange membranes are also studied in detail. It is found that the diameters of the Nafion molecular aggregates in variable solutions decrease with an increase in the solvent dielectric constant (epsilon) and a decrease in the gap of the solubility parameters (delta) between the resin and the solvent. The micromorphology of Nafion is further examined by means of transmission electron microscopy, small-angle X-ray scattering, and X-ray diffraction. It is found that the membrane cast from a Nafion-2-propanol/water dispersion with E value of 4238 and a delta gap of 0.01 (cal cm(-3))(1/2) has a better ion cluster arrangement, smaller ion cluster size (approximately 13 angstrom), and higher crystallinity (16.7%) than the other samples. The electrochemical properties of the formed membranes are further investigated as a function of temperature, relative humidity, and the solubility parameter of the applied solvents. The results demonstrate that the electrochemical performance is strongly influenced by the solvent-induced microstructure of the backbone and the ionic clusters in the perfluorosulfonic acid membrane. (C) 2014 Elsevier B.V. All rights reserved.