Dynamics of Fe cations in Nafion membranes studied by nuclear resonant quasielastic scattering of synchrotron radiation

Citation
R. Haruki et al., Dynamics of Fe cations in Nafion membranes studied by nuclear resonant quasielastic scattering of synchrotron radiation, J PHYS JPN, 69(12), 2000, pp. 4049-4054
Citations number
12
Categorie Soggetti
Physics
Journal title
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN
ISSN journal
00319015 → ACNP
Volume
69
Issue
12
Year of publication
2000
Pages
4049 - 4054
Database
ISI
SICI code
0031-9015(200012)69:12<4049:DOFCIN>2.0.ZU;2-J
Abstract
Nuclear resonant quasielastic scattering from ferrous cations in ion-exchan ge Nafion membranes was measured at room temperature, and the intrinsic dyn amics of the cations inside the spherical regions surrounded by the sulfoni c groups of Nafion was studied. For the analysis, the formula of nuclear re sonant absorption for a particle diffusing in a sphere with an impermeable surface was derived. The formula indicates that the effect of the surface u pon the diffusive motion is small if the radius of the sphere is larger tha n a critical value; in the case of Fe-57 ions, the value is about 2 Angstro m. As the radius of the spherical regions in our Nafion samples is estimate d to be about 5 Angstrom, the existence of the surface can be ignored and t he intrinsic dynamics of Fe cations can be extracted. The diffusion coeffic ient estimated from the least squares fit was (1.12 +/- 0.13)x10(-5) cm(2)/ s for 15 wt% water content. This value is in good agreement with that of Fe cations in an HCL solution. As a result, Fe cations in Nafion diffuse as f reely as those in solutions.