title: Ionic liquids: not only structurally but also dynamically heterogeneous.
abstract: In recent years, the complex and heterogeneous structure of ionic liquids has been demonstrated; however, the consequences on the dynamics have remained elusive. Here, we use femtosecond IR spectroscopy to elucidate the local structural dynamics in protic alkylammonium-based ionic liquids. The structural relaxation after an ultrafast temperature increase, following vibrational excitation and subsequent relaxation of the N-D (or N-H) stretching vibration, is found to vary substantially between the ionic and hydrophobic subdomains. The dynamics in the ionic domains are virtually unaffected by the alkyl chain length and is, therefore, decoupled from viscosity. Equilibration within the hydrophobic subdomains, as evident from the dynamics of the C-H stretching vibration, is faster than that in the ionic domains and shows a remarkably low thermal activation.
authors.affiliation: Department for Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany); State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an, Shaanxi, 710119 (China).
authors.forename: Zhuan-Ping
authors.initials: ZP
authors.lastname: Zheng
authors.forename: Wen-Hui
authors.initials: WH
authors.lastname: Fan
authors.forename: Soham
authors.initials: S
authors.lastname: Roy
authors.forename: Kamila
authors.initials: K
authors.lastname: Mazur
authors.forename: Andreas
authors.initials: A
authors.lastname: Nazet
authors.forename: Richard
authors.initials: R
authors.lastname: Buchner
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn
authors.forename: Johannes
authors.initials: J
authors.lastname: Hunger
keywords: IR spectroscopy; ionic liquids; thermal equilibration