Browsing by Author "Pak, Y.S."

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    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.