The morphology of Nafion: are ion clusters bridged by channels or single ionic sites?

Nafion{sup Ri}s perfluorosulfonated ionomer membrane that is used as a solid polymer electrolyte in H{sub 2}/O{sub 2} fuel cells due to its excellent chemical stability and high ionic conductivity. This paper describes experiments designed to probe the morphology of water-swollen and air-dried Nafion{sup Rm}embranes using small angle X-ray scattering and fitting the resulting data to an interparticle model. For air-dried Nafion membranes the average diameter of ionic clusters was found to be 2.24 nm ; for wet Nafion membranes of the -SO{sub 3}H groups the average ionic cluster diameter was 4.10 nm. The minimum and maximum distances of separation between the surfaces of two adjacent hydrated clusters were 0.30 nm and 0.88 nm, respectively. These distances may be bridged by single hydrated ionic sites, but since there are several ionic sites per ionic core that reside outside the core, it is suggested that the connection between ionic cores most likely occurs via multiple single ion sites. 40 refs., 3 tabs., 4 figs.