Quasielastic Neutron Scattering Investigations of Ionic Liquids and Comparison to Complementary Methods

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Using our own cold neutron time-of-flight spectrometer FOCUS at the Swiss spallation source SINQ of the Paul-Scherrer-lnstitute in Villigen (Switzerland) we would like to perform systematically a series of quasielastic neutron scattering (QENS) experiments to elucidate the dynamics in ionic liquids on atomistic scales of space and time. As model system we suggest [N-alkyl-N-methyl-pyrrolidinium] bis-(trifluoromethylsulfonyl) imide with different alkyl chains. Since protons are the dominant scattering centers, QENS on these systems probes the cation dynamics. It is known from literature, and confirmed by a QENS test experiments, that the hydrogen atoms in the cation side chains perform localized rotational motions. In order to study the diffusional dynamics these side chains have to be deuterated, so the hydrogen atoms at the stiff cation backbone can be observed. From model-independent data evaluation the essential features of the dynamics will first be conceived. Afterwards the data evaluation will be done in terms of appropriate theoretical models, for instance the two-state-model, which could give insight into the kinetics of ion pair formation. At a later stage also QENS with polarized neutron and neutron polarization analysis is intended in order to distinguish between incoherent and coherent QENS and thus between single particle diffusion and collective diffusion.