Self-diffusion micromechanism in Nafion studied by 2H NMR relaxation dispersion.

Field Cycling (FC) 2H nuclear magnetic resonance (NMR) relaxometry was applied to study dynamics in Nafion NR 212 in the temperature range from 300 K to 190 K and water content of λ = 8.2. The sensitive time window of FC was extended up to eight decades using the temperature-frequency superposition principle and master curve. The rotational correlation times obtained from 2H FC NMR coincide with translational correlation times gained from static field 2H NMR diffusometry in the temperature range applied. This fact means that a long-range mass transport in Nafion is coupled to molecular rotations. It is assumed that confined water in Nafion has more ordered oxygen sublattices as compared with bulk water, on a short range is similar to ice. We discuss the possible role of D and L defects, typical for the ordered ice structure and using this concept to describe the processes of self-diffusion of confined water in Nafion, as well as the similarity of temperature and humidity dependence of self-diffusion and proton conductivity.

Citation

Elena A Galitskaya, Alexei F Privalov, Michael Vogel, Ivan A Ryzhkin, Vitaly V Sinitsyn. Self-diffusion micromechanism in Nafion studied by 2H NMR relaxation dispersion. The Journal of chemical physics. 2021 Jan 21;154(3):034904

PMID: 33499620

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