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Localized relaxational dynamics of succinonitrile

journal contribution
posted on 20.08.2009, 00:00 authored by L van Eijck, A Best, S Long, F Fernandez-Alonso, D MacFarlane, Maria ForsythMaria Forsyth, G Kearley
Succinonitrile (N≡C—CH2—CH2—C≡N) is a good ionic conductor, when doped with an ionic compound, at room temperature, where it is in its plastic crystalline phase (Long et al. Solid State Ionics 2003, 161, 105; Alarco et al. Nat. Mater. 2004, 3, 476). We report on the relaxational dynamics of the plastic phase near the two first-order phase transitions and on the effect of dissolving a salt in the plastic matrix by quasi-elastic neutron scattering. At 240 K, the three observed relaxations are localized and we can describe their dynamics (τ ≈ 1.7, 17, and 140 ps) to a certain extent from a model using a single molecule that was proposed by Bée et al. allowing for all conformations in its unit cell (space group IM3M). The extent of the localized motion as observed is however larger than that predicted by the model and suggests that the isomerization of succinonitrile is correlated with a jump to the nearest neighbor site in the unit cell. The salt containing system is known to be a good ionic conductor, and our results show that the effect of the ions on the succinonitrile matrix is homogeneous. Because the isomerizations and rotations are governed by intermolecular interactions, the dissolved ions have an effect over an extended range. Due to the addition of the salt, the dynamics of one of the components (τ ≈ 17 ps) shows more diffusive character at 300 K. The calculated upper limit of the corresponding diffusion constant of succinonitrile in the electrolyte is a factor 30 higher than what is reported for the ions. Our results suggest that the succinonitrile diffusion is caused by nearest neighbor jumps that are localized on the observed length and time scales.

History

Journal

Journal of physical chemistry Part C : nanomaterials and interfaces

Volume

113

Issue

33

Pagination

15007 - 15013

Publisher

American Chemical Society

Location

Washington, D.C.

ISSN

1932-7447

eISSN

1932-7455

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2009, American Chemical Society