Browsing by Author "Chen, R.S."

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Deuteron and Oxygen-17 NMR Studies of Molecular Motion in Methanol-Saturated Nafion Membranes
(MRS Proceedings, 1993) Chen, R.S.; Jayakody, J.R.P.; Greenbaum, S.G.
Deuteron and oxygen-17 NMR linewidth and spin-lattice relaxation measurements in Nafion-117 films containing methanol at ?75% and ?100% saturation are reported. Molecular motion probed by room temperature measurements in stretched films and low T measurements in unstretched films is found to be quite rapid compared to previous results obtained for Nafion-117 containing water.
High pressure studies of hydrated NAFION membranes: Dielectric relaxation and deuteron NMR
(Solid State Ionics, 1993) McLin, M.G.; Wintersgill, M.C.; Fontanella, J.J.; Chen, R.S.; Jayakody, J.R.P.; Greenbaum, S.G.
Audio frequency electrical conductivity/dielectric relaxation and nuclear magnetic resonance studies of NAFION-117 have been carried out at pressures up to 0.3 GPa (3 kbar). For some samples, the electrical conductivity exhibits dispersion typical of hopping conductivity in an amorphous material, ?=?0?m. The values of m are sample dependent and vary from about 0.55 to 0.75. In addition, the values of m are not strongly pressure sensitive. At a given frequency, the electrical conductivity tends to decrease as pressure increases and yield activation volumes on the order of 5 to 10 cm3/mol. The activation volume determined from the NMR spin-lattice relaxation time measurements are also sample dependent. The data shown correspond to an activation volume of about 8.6 cm3/mol. The results of the high pressure electrical conductivity studies also yield activation volumes on the order of that determined via NMR.
Studies of Water in Nafion Membranes: Using Deuteron and Oxygen?17 Nuclear Magnetic Resonance, and Dielectric Relaxation Techniques
(Journal of Electrochemical Society, 1993) Chen, R.S.; Jayakody, J.R.P.; Greenbaum, S.G.; Pak, Y.S.; Xu, G.; McLin, M.G.; Fontanella, J.J.
Deuteron and oxygen-17 nuclear magnetic resonance measurements and dielectric relaxation studies of Nafion-117 membranes with variable water content (approximately 5-18% by weight) have been carried out. Glassy behavior of the water domains at low temperature, below ca. 200 K, is evidenced by the specific nature of the 2H NMR line shapes. Activation energies extracted from H spin-lattice relaxation data on the high temperature side of the T1 minimum exhibit a steady increase with increasing water content. In spite of a high degree of molecular mobility, angular-dependent spectra in both as-received and stretched samples reflect considerable anisotropy of the host polymer. A dielectric loss peak is observed which previously has been attributed to the glass transition of the aqueous domains.