MOSSBAUER-SPECTROSCOPY OF NAFION POLYMER MEMBRANES EXCHANGED WITH FE-2+, FE-3+, AND EU-3+

In the reported experiments, Moessbauer spectra of ″Nafion″ perfluoronated acid membranes exchanged with iron or europium have been studied as a function of ion concentration, water content, temperature, and applied magnetic field in order to characterize the ionic phase in these materials. In Fe**2** plus Nafion, the spectrum is independent of water content above 6 wt %, and is typical of fully hydrated, isolated Fe**2** plus (H//2O)//6 species. The isomer shift, quadrupole splitting, and linewidth all change continuously below 6 wt% water, indicating a range of environments for the iron. For Fe**3** plus Nafion, ions in several distinct environments can be identified on the basis of their magnetic properties. It is associated with paramagnetic iron having other iron ions in the neighborhood, and also with iron ions located in the interior of small groups or chains formed from dimers. There is no iron belonging to magnetically ordered clusters involving hundreds of ferric ions of the type found in some other ionomers. All the exchanged ions belong to the ionic phase, and none are associated with the polymer backbone.