LI-7 NUCLEAR MAGNETIC SPIN-LATTICE RELAXATION INVESTIGATION OF LITHIUM TRIFLUOROMETHANESULFONATE AND ITS COMPLEX WITH POLY(ETHYLENE OXIDE)

A Li-7 NMR spin-lattice relaxation investigation over the temperature range 200-340 K is reported for a polycrystalline sample of LiCF3SO3 a nd a sample of poly(ethylene oxide) (PEO)-LiCF3SO3 with an O:Li molar ratio of 3.5:1. In both cases the Li-7 magnetization recoveries were f ound to be single exponential and so the spin-lattice relaxation could be characterized by a single time constant, T-1(Li-7). The Li-7 spin- lattice relaxation in polycrystalline LiCF3SO3 is shown to be dominate d by a mechanism that involves the modulation of Li-7,F-19 magnetic di polar interactions due to the reorientational motions of the CF3 group s about their threefold symmetry axes. The Arrhenius parameters derive d for this motion are shown to be in good agreement with those determi ned in an earlier F-19 spin-lattice relaxation study. The Li-7 spin-la ttice relaxation time measurements in the 3.5:1 PEO-LiCF3SO3 sample ar e taken to reflect the properties of the single crystalline complex, w hich is known to be present in PEO-LiCF3SO3 mixtures. The extent to wh ich magnetic dipolar relaxation processes contribute to Li-7 spin-latt ice relaxation in this complex is discussed in some detail. It is demo nstrated that modulation of Li-7, H-1 magnetic dipolar interactions, d ue to backbone motions of the PEO chains, probably makes a significant contribution. There also appear to be strong links between the motion al processes responsible for both H-1 and Li-7 spin-lattice relaxation .