Hierarchical structure and dynamics of an ionic liquid 1-octyl-3-methylimidazolium chloride

Abstract

We have performed the heat capacity, neutron diffraction, and neutron quasielastic scattering measurements of an ionic liquid 1-octyl-3-methylimidazolium chloride (C8mimCl). The heat capacity data revealed that C8mimCl exhibits a glass transition with a large heat capacity jump at T(g) = 214 K, which is lower than T(g) of C4mimCl with a shorter alkyl-chain. In the neutron diffraction measurement for a deuterated analogue, d-C8mimCl, the peaks associated with the inter-domain, inter-ionic, and inter-alkyl-chain correlations appeared at (3, 11, and 14) nm(-1), respectively. The temperature dependence of these peaks indicates that the packing of the alkyl-chains becomes more compact and the domains become more vivid and larger as decreasing temperature. The quasielastic neutron scattering measurements using neutron spin echo and time-of-flight type instruments demonstrated that C8mimCl has faster relaxations probably owing to the alkyl-group and a slower relaxation owing to the ions. The latter relaxation, which is related to the glass transition, is of non-exponential as in the α relaxation of glass-forming molecular liquids. The relaxation of domains could not be observed in the present experiment but should have relaxation times longer than 100 ns. This is the first report to clarify temperature dependence of the hierarchical structure and relaxations simultaneously for a typical ionic liquid.

Cation and anion dynamics in supercooled and glassy states of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate: Results from13C,31P, andEndo1, Widgeon2, Yu3 et al. 2012Phys. Rev. B220150View full textAdd to dashboardCite

“…It is to be noted that a number of previous studies attributed the microscopic origin of β relaxations in RTILs to hydrogen dynamics in the alkyl groups of cations. 16,18,30,75,76 The results presented in this study do not contradict that scenario but indicate that anionic motions in RTILs can also contribute to the β relaxation process. However, a mechanistic understanding of the temporal coupling between the cationic and anionic motions associated with the β relaxation remains lacking at this stage.…”

Inelastic neutron scattering study on boson peaks of imidazolium-based ionic liquids

“…[19,20]. The protonated CnminI (n = 3, 4, 6) were provided by Prof. M. Nakakoshi in Yokohama National University.…”

Neutron scattering studies on short- and long-range layer structures and related dynamics in imidazolium-based ionic liquids

“…c) Electronic mail: yamamuro@issp.u-tokyo.ac.jp During the past decade, great progress has also been made in fundamental scientific studies. [4][5][6] The structural investigations for CnmimX with n < 10 have been performed by using x-ray and neutron diffraction (ND) techniques [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and molecular dynamics (MD) simulations. 12,17,[22][23][24][25][26][27][28][29][30] In these studies, a characteristic peak indicative of Q low , which is called "low-Q peak" in this paper, appeared at Q low ≈ 0.3 Å −1 in addition to the peaks at Q ion ≈ 1 Å −1 corresponding to the correlation among ions and at Q alkyl ≈ 1.5 Å −1 corresponding mainly to the correlation among alkylchains (Fig.…”