Polymer Relaxational Dynamics Associated With Ionic Conduction in Confined Geometry
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POLYMER RELAXATIONAL DYNAMICS ASSOCIATED WITH IONIC CONDUCTION IN CONFINED GEOMETRY J.-M. Zanotti1,2, L.J. Smith3, E. Giannelis4, P. Levitz5, D.L. Price1,6 and M.-L. Saboungi3,7 1 Intense Pulsed Neutron Source, Argonne Nat. Lab., Argonne, IL 60439, USA 2 Laboratoire Leon Brillouin (CEA-CNRS), CEA Saclay, 91191 Gif/Yvette cedex, France 3 Material Science Division, Argonne Nat. Lab., Argonne, IL 60439, USA 4 Department of Materials Science and Engineering, Cornell University, Ithaca, NY, USA 5 LPMC (CNRS), Ecole Polytechnique, Palaiseau, France 6 CRMHT (CNRS), Avenue de la Recherche Scientifique, 45071 Orléans, France 7 CRMD(CNRS), Avenue de la Recherche Scientifique, 45071 Orléans, France
ABSTRACT Results of a quasi-elastic incoherent neutron scattering study of the influence of confinement on polyethylene oxide (PEO) and (PEO)8Li+[(CF3SO2)2N]- (or (POE)8LiTFSI) dynamics are presented. The confining media is Vycor, a silica based hydrophilic porous glass. We observe a strong slowing down of the bulk polymer dynamics under presence of Li salt. The confinement also affects dramatically the apparent mean-square displacement of the polymer. As supported by DSC measurements, the PEO melting transition at 335 K is strongly attenuated under confinement, suggesting that confinement modifies the global structure of the system, increasing the fraction of amorphous PEO by respect to crystalline phase. Local relaxational PEO dynamics is successfully described by the DLM (DejeanLaupretre-Monnerie) model usually used to interpret NMR spin-lattice relaxation time data. The scattering vector dependence of the correlation times deduced from inelastic neutron scattering data is found to obey a power-law dependence. DSC and preliminary ionic conduction measurements are also presented.
INTRODUCTION Conception and industrial production of economically viable fuel cells [1] is a central issue for the developing of non-polluting vehicles. Up to date many studies have shown the interest and the feasibility of hybrid cells where organic and inorganic components are used. One of the most studied systems is PEO (polyethylene oxide) complexed by Li salts. Polymer segmental motions and ionic conductivity are closely related [2]. Bulk PEO is actually a biphasic system where an amorphous and a crystalline state (Tm ≈ 335 K) coexist. A key to improve ionic conduction in those systems is therefore a significant increase of the amorphous phase fraction where lithium conduction is known to mainly take place [3]. Upon this issue, operation above 80oC is satisfactory but such high temperatures requirements will drastically reduce any broad consumer use. Confinement is known to strongly affect properties of condensed mater and in particular the collective phenomena inducing crystallization [4]. A possible alternative solution to this high temperature mode seems therefore the confinement of the polymer matrice. Polymer-silicate nanocomposites have been proposed and are under extensive study [5,6].
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Structure of polymer chains confined
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