ORIENTATION EFFECTS IN THE DEUTERIUM NMR-SPECTROSCOPY OF PERFLUORINATED IONOMER MEMBRANES

The properties of water in Nafion(R) and Dow perfluorinated ionomer membranes in their protonated forms were investigated by proton and deuterium NMR spectroscopy. The H-2 quadrupolar splittings were shown to be dependent on the orientation of the membranes in the magnetic field as well as on their water content. The larger quadrupolar splittings found for Nafion are attributed to a greater degree of orientational order compared to the Dow samples. Hydrogen bonding, as evidenced by H-1 and H-2 chemical shifts, was very similar in the two types of membrane for a given relative humidity. The H-2 spin-lattice relaxation times (T1) were 93 and 109 ms for Nafion and Dow respectively at 300 K and 100% relative humidity, compared to 612 ms for D2O in 1:9 D2O:H2O. The temperature dependence of the T1 values was similar for the two membranes in the range 280-320 K and activation energies for molecular reorientation were estimated at 22 +/- 2 kJ mol-1, comparable to that for pure water in the same temperature range.