SMALL-ANGLE SCATTERING STUDY OF WATER-SWOLLEN PERFLUORINATED IONOMER MEMBRANES

A structural study using both small-angle X-ray and neutron scattering (respectively SAXS and SANS) of water-swollen perfluorosulfonated ion omer (PFSI) membranes is presented. The comparison between the SAXS an d SANS spectra combined with the analysis of both the scattering invar iant and the Pored behavior of the scattering curves confirms the phas e separation between the water peels and the perfluorinated matrix. Th e experimental data obtained in absolute units were analyzed in terms of the different models proposed for ionomers, and the local order mod el appears as the best model for describing the structure of swollen P FSI membranes. The size of the water pools and the number of ionic gro ups per ionic aggregate deduced from the analysis of the asymptotic be havior of the scattering curve at large angles compare well with the v alues deduced from the local order model. The SAXS spectra of swollen PFSI membranes are presented for the first time over an extended angul ar range covering 3 decades of angles using an ultra-small-angle scatt ering camera. The study of the small-angle upturn in intensity at very low angles revealed the existence of large-scale fluctuations.