We have studied the structure and dynamics of alkylmethylimidazolium salts CnmimX (n: alkyl-carbon number, X: anion), which is the most popular ionic liquid, by means of neutron scattering techniques. The most characteristic feature of CnmimX is the nano-structure consisting of the polar-domains with the imidazolium rings and anions and the non-polar domains with alkyl-chains of the cations. Our neutron diffraction works on C8mimX (X = Cl, PF6, TFSI) [1,2] have demonstrated that a diffraction peak associated with the nano-structure appeared at Q = ca. 3 nm-1, while a peak due to the ionic correlation appeared at ca. 10 nm-1. The intensity of the lower-Q peak drastically increases with decreasing temperature. There is another broad peak mainly related to the alkyl-chain correlation at ca. 15 nm-1. We have also investigated the dynamics of CnmimX (n = 4-8, X = Cl, PF6, NO3, TF, FSI, TFSI) by using several time-of-flight and neutron spin echo spectrometers in JRR-3 (Japan), ISIS (UK), and NIST (USA). Figure 1 shows the temperature dependence of the relaxation times in C8mimTFSI. There are 3 relaxations corresponding to the correlations mentioned above. This is the first relaxation map showing the overall dynamic feature of the ionic liquid.[1] O. Yamamuro et al., J. Chem. Phys. 135, 054508 (2011). [2] M. Kofu et al., J. Phys. Chem. B 117, 2773 (2013).

Neutron scattering studies on structures and dynamics of imidazolium-based ionic liquids

248th National Meeting (2014)

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