A Nuclear Magnetic Resonance Study of Water Behavior in PTFE Ionomer Membranes

High field 1H nuclear magnetic resonance has been conducted to investigate the ionic motion in perfluorinated ionomer membranes from Dow Chemical (XUS). Two distinctive proton resonance peaks were found in the vacuum‐dried samples. The designation of the upfield peak to the 1Hs associated with the sulfonate groups was proved by the fact that the intensity of the low‐field peak increases drastically in the less‐dried specimens. An asymmetrical V‐curve was observed for the spin‐lattice relaxation time (T1) plotted against the reciprocal temperature with samples saturated with H2O , showing a distribution of the relaxation times centered around 0.3 ns. At all H2O concentrations the major linewidths were essentially constants above certain transition temperatures (Tt) and were broadened by more than one order of magnitude at reduced temperatures, yielding a similar activation energy to that from dc conductivity measurement. Quadrupole splitting was observed in the 2H spectrum at 360 K, and it reduced to a single resonance line when the sample was cooled, showing that in XUS ionomer the averaging of the quadrupole interaction is stronger than that in NafionR.