ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Mössbauer 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 every sample, the recoil-free fraction falls to zero at a temperature which decreases from 280 to 220 K with increasing water content. The sudden fall in recoil-free fraction corresponds to a glass transition in the ionic phase rather than its melting point. In Fe2+ Nafion, the spectrum is independent of water content above 6 wt%, and is typical of fully hydrated, isolated Fe2+(H2O)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 Fe3+ Nafion, ions in several distinct environments can be identified on the basis of their magnetic properties. Isolated Fe3+ species (Fe-Fe distances greater than 12 Å) showing paramagnetic hyperfine structure in their 4.2-K spectra predominate in slightly neutralized samples, and in those with high water content. The proportion of dimers, whose quadrupole splitting is about 1.7 mm/s, increases with increasing iron content or decreasing water content. A third component of the spectra has a quadrupole splitting of 0.4 mm/s. 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.
Additional Material:
14 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1982.180200404
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