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    Two new siloxanic proton conducting membranes: Part II. Proton conductivity mechanism and NMR study
    (Electrochimica Acta, 2005) di Noto, V.; Vittadello, M.; Kalfan, A.N.; Greenbaum, S.G.
    The synthesis and structural characterization of two types of membranes with formulas {Si(CH3)3O[Si(CH3)HO]21.26-[Si(CH3)((CH2)3SO3H)O]1.8-[Si(CH3)((CH2)3Si(CH3)2O-)-O]14-Si(CH3)3}n (A) and {Si(CH3)3O[Si(CH3)HO]21.26-[Si(CH3)((CH2)3SO3H)O]1.8-[Si(CH3)((CH2)3(Si(CH3)2O-w))-Ov][Si(CH3)((CH2)3Si(CH3)2O-)-O]14?vSi(CH3)3}n (B), (w=20.31), were previously proposed. The ac electrical response of A and B was fully characterized in the 40 Hz?2 MHz frequency region by studying the impedance spectra in the medium and low frequency regions by equivalent circuits and complex dielectric spectra at high frequency in terms of dielectric relaxation modes. Results demonstrated that A and B conduct ionically by means of a proton exchange event which occurs via a vehicular mechanism between neighboring water clusters formed by water molecules aggregated around each sulfonic acid group of the siloxane side chains. The proton conductivities at 115�C of ca. 1.9 ? 10?3 and 1.8 ? 10?4 S cm?1 of fully hydrated membranes A and B, respectively, classify these silicone networks as good proton conductors. Membrane B was chosen for a closer investigation using NMR spectroscopy. Solid state 29Si MAS NMR experiments gave further insight about the three-dimensional structure. Proton diffusion measurements provided some encouraging results about proton dynamics of this membrane signaling the great potential of siloxanic based proton conductors.
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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.