THE LOCAL ENVIRONMENT FOR SODIUM-CATIONS IN POLY(PROPYLENE GLYCOL) FROM NMR AND POSITRON-ANNIHILATION STUDIES

Results of Na-23 NMR investigations of poly(propylene glycol) (PPG) complexed with sodium salts are compared with Na-22 positron annihilation studies on the same complex. From Na-23 NMR, the sodium cation motion in PPG is well described by a single exponential correlation function indicating a liquid-like environment down to the glass transition, T-g. The spin-spin and spin-lattice relaxation of the sodium nucleus is dominated by the nuclear quadrupolar interaction. The observed relaxation results are consistent with the theory for quadrupolar relaxation when the correlation time, tau(c), is greater than the reciprocal of the rigid lattice line width. The pick-off lifetimes and intensities (tau(3), I-3) of positrons emitted by Na-22 dissolved in PPG give information about microscopic density fluctuations as a function of salt concentration and temperature. Both Na-23 NMR and Na-22 positron annihilation probe the polyether-salt system on the nanosecond timescale. An inverse correlation between tau(c) and tau(3) is shown. Also, evidence for a critical temperature, T-c, above which the polyether-salt system behaves as a monatomic fluid independent of salt concentration and polymer molecular weight and below which as a polymer-salt glass-forming system, is shown.