Hierarchical Structure and Dynamics of an Ionic Liquid 1-Octyl-3-methylimidazolium Chloride

Published

August 3, 2011

Author(s)

Osamu Yamamuro, Takeshi Yamada, Maiko Kofu, Masamichi Nakakoshi, Michihiro Nagao

Abstract

We have performed the heat capacity, neutron diffraction, and neutron quasielas- tic scattering measurements of an ionic liquid 1-octyl-3-methylimidazolium chloride (C8mimCl). The heat capacity data revealed that C8mimCl exhibits a glass tran- sition 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, respec- tively. 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 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 re- laxation 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.

Citation

Journal of Chemical Physics

Volume

135

Issue

5

Pub Type

Journals

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Keywords

ionic liquid, dynamics, neutron spin echo, domain

Citation

Yamamuro, O. , Yamada, T. , Kofu, M. , Nakakoshi, M. and Nagao, M. (2011), Hierarchical Structure and Dynamics of an Ionic Liquid 1-Octyl-3-methylimidazolium Chloride, Journal of Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=908316 (Accessed April 29, 2024)