Molecular Dynamics Simulations and Vibrational Spectroscopic Studies of Local Structure in Tetraglyme:Sodium Triflate (CH3O(CH2CH2O)4CH3:NaCF3SO3) Solutions

An oligomeric model for poly(ethylene oxide), tetraglyme, with NaCF3SO3 at an ether oxygen:Na+ ratio of 10:1 was used to represent the amorphous phase of PEO:salt systems in molecular dynamics simulations at 300 K and 400 K. Na+−tetraglyme interactions were examined by calculating chain dimensions,...

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Published in:The journal of physical chemistry. B 2002-05, Vol.106 (18), p.4878-4885
Main Authors: Dong, Haitao, Hyun, Jin-Kee, Rhodes, Christopher P, Frech, Roger, Wheeler, Ralph A
Format: Article
Language:English
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Summary:An oligomeric model for poly(ethylene oxide), tetraglyme, with NaCF3SO3 at an ether oxygen:Na+ ratio of 10:1 was used to represent the amorphous phase of PEO:salt systems in molecular dynamics simulations at 300 K and 400 K. Na+−tetraglyme interactions were examined by calculating chain dimensions, dihedral angle population distribution, and conformational triad populations of coordinating tetraglyme chains. All results consistently show that the Na+−ether oxygen coordination induces more compact chains by enforcing a gauche conformation for C−C bonds and introducing a strong preference for tgt conformations in the C−O−C−C−O−C bond sequence. Na+−O(tetraglyme) and Na+−O(triflate) radial distribution functions reveal that triflate ions contribute more oxygens (4.9 at 300 K and 5.3 at 400 K) than tetraglyme (2.2 at 300 K and 2.0 at 400 K) to the first coordination shell of Na+. Populations of aggregates consisting of a triflate ion coordinated to 0−3 Na+ were available from vibrational spectra and were also calculated from equilibrated trajectories. Both results agree well, and the computational results indicate that Na+−CF3SO3 - association increases with increasing temperature. The results are compared with results from a previously studied tetraglyme:LiCF3SO3 system. Unlike Li+ in the tetraglyme:LiCF3SO3 system, bidentate coordination of Na+ by CF3SO3 - becomes more favorable at the higher temperature, at the expense of monodentate and tridentate coordination.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp013914w