Self-diffusion micromechanism in Nafion studied by 2H NMR relaxation dispersion
The Field Cycling (FC) 2H NMR relaxometry was applied to study dynamics in Nafion NR 212 in the temperature range from 300K to 190K and water content l=8.2. The sensitive time window of FC was extended up to 8 decades using 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 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 sublattice as compared with bulk water, on a short range is similar to ice. We discuss the possible role of D and the L defects, typical for ordered ice structure and using this concept to describe the processes of self-diffusion of confined water in Nafion, as well as similarity of temperature and humidity dependence of self-diffusion and proton conductivity.