Browsing by Author "Suarez, S.N."

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    A Fundamental Study of the Transport Properties of Aqueous Superacid Solutions
    (Journal of Physical Chemistry B, 2010) Suarez, S.N.; Jayakody, J.R.P.; Greenbaum, S.G.; Zawodzinski, T.; Fontanella, J.J.
    An extensive investigation of the transport properties of aqueous acid solutions was undertaken. The acids studied were trifluoromethanesulfonic (CF3SO3H), bis(trifluoromethanesulfonyl)imide [(CF3SO2)2NH], and para-toluenesulfonic (CH3C6H4SO3H), of which the first two are considered superacids. NMR measurements of self-diffusion coefficients (D), spin?lattice relaxation times (T1), and chemical shifts, in addition to ionic conductivity (?), viscosity (?), and density measurements, were performed at 30 �C over the concentration range of 2?112 water to acid molecules. Results showed broad maxima in ? for all three acids in the concentration range of 12?20 water to acid molecules. This coincided with minima in anion Ds and is attributed to a local molecular ordering, reduced solution dielectric permittivity, and increased ionic interactions. The location of the maxima in ? correlates with what is observed for hydrated sulfonated perfluoropolymers such as Nafion, which gives a maximum in ionic transport when the ratio of water to acid molecules is about 15?20. Of the three acids, bis(trifluoromethanesulfonyl)imide was found to be the least dependent on hydration level. The occurrence of the anticorrelation between the ionic conductivity maximum and the anion self-diffusion minimum supports excess proton mobility in this region and may offer additional information on the strength of hydrogen bonding in aqueous media as well as on the role of high acid concentration in the Grotthuss proton transport mechanism.
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    A multinuclear NMR study of ion transport in P(EO)nLiBETI complexes
    (Solid State Ionics, 2005) Suarez, S.N.; Abbrent, S.; Jayakody, J.R.P.; Greenbaum, S.G.; Shin, J.H.; Passerini, S.
    A study of ion transport in P(EO)nLiBETI complexes was undertaken, using both AC impedance and nuclear magnetic resonance (NMR) spectroscopy. 1H, 7Li and 19F NMR techniques were used to investigate structure and dynamics as a function of temperature for n=3, 6, 8, 12 and 20. Spin?lattice relaxation times (T1) and spectral information were obtained from ?50 to 100 �C. Variable temperature self-diffusion coefficients (D) and ionic conductivity (?) measurements were also performed. Anion diffusion (DF) results displayed a dependence on available free volume, increasing with decreasing salt concentration. On the other hand, cation diffusion (DLi) results did not follow this trend. DLi for n=3 and 6 suggest the presence of ionic mobility in the crystalline phase, with a significant rise above the melting point. A transition from a crystalline to amorphous phase dominated ion transport occurs at n=8. This is supported by ? results, which exhibited a VTF type of behavior for n?8 that is associated with ion transport in the amorphous phase.