Molecular Dynamics in 1-Alkyl-3-Methylimidazolium Bromide Ionic Liquids: A Reanalysis of Quasielastic Neutron Scattering Results.

摘要

We have reanalyzed quasielastic neutron scattering data measured for three prototypical ionic liquids characterized by increasingly longer alkyl chains using two standard models of different complexity. The first one contains only two main components representing a long-range translational diffusion process plus a faster localized-like motion. The second model includes an additional component in order to account for the possibility of having more than one type of localized motion with different characteristic time scales. Our results show the complexity of the relaxation landscape of ionic liquids, indicating that even the more complex model provides only a qualitative average picture of such complex dynamics. The comparison of both models allows to asses also the robustness of the parameters obtained from the fits. Finally the results for the three different ionic liquids are compared in order to determine the effect of the length of the alkyl chain in the translational dynamics of ionic liquids, showing a clear decrease in diffusivity when passing from the ethyl (n=2) to the butyl (n=4) alkyl chain, but a much smaller effect when adding two extra C atoms to the chain.