Cation exchange membranes by radiation-induced graft copolymerization of styrene onto PFA copolymer films. IV. Morphological investigations using X-ray photoelectron spectroscopy

Morphological investigations of poly(tetrafluoroethylene-co-perfluorovinyl ether) (PFA)-g-polystyrene sulfonic acid membranes prepared by radiation-in duced graft copolymerization of styrene onto PFA films followed by sulfonat ion were performed by X-ray photoelectron spectroscopy. The analyzed materi als included grafted film and sulfonated membrane samples having various de grees of grafting. Original PFA film was used as a reference material. The results of the X-ray photoelectron spectral analysis show that PFA film und ergoes changes in terms of chemical compositions and binding energies of it s basic elemental components under the influence of membrane preparation pr ocedure, i.e., grafting and sulfonation. The chemical compositions of the s urfaces of the membranes were found to be dependent on the degree of grafti ng unlike the binding energies of their elemental components (C, F, O, and S), which were found to be independent of the degree of grafting. The atomi c ratio of F/C was found to decrease drastically with the increase in the d egree of grafting and the membranes were found to have almost pure hydrocar bon structure at the layers close to their surfaces where degradation is su ggested to be concentrated. The results of these investigations suggest tha t the morphology of the membranes plays an important role in the chemical d egradation of the membranes. (C) 2000 John Wiley & Sons, Inc.