High-frequency dynamics and test of the shoving model for the glass-forming ionic liquid Pyr14-TFSI

Kira L. Eliasen, Henriette W. Hansen, Filippa Lundin, Daniel Rauber, Rolf Hempelmann, Tage Christensen, Tina Hecksher, Aleksandar Matic, Bernhard Frick, Kristine Niss*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

Abstract

In studies of glass-forming liquids, one of the important questions is to understand to which degree chemically different classes of liquids have the same type of dynamics. In this context, room-temperature ionic liquids are interesting because they exhibit both van der Waals and Coulomb interactions. In this work we study the α relaxation and faster relaxation dynamics in the room-temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14-TFSI). The paper presents quasielastic neutron and shear mechanical spectroscopy data measured over seven decades in frequency (10-3-104 Hz). The use of these two methods in combination reveal the α relaxation and four separate, faster modes. Two of these faster modes, based on the partial deuterations, can be assigned to the methyl group and the methyl end of the butyl chain of the cation. The neutron data are also used to determine the mean-square displacement (MSD) on the nanosecond timescale. It is shown that the temperature dependence of the MSD can account for the super-Arrhenius behavior of the α relaxation as predicted by the shoving model [Dyre, Rev. Mod. Phys. 78, 953 (2006)RMPHAT0034-686110.1103/RevModPhys.78.953], similarly to what is seen in simpler glass-forming liquids.

Original languageEnglish
Article number065606
JournalPhysical Review Materials
Volume5
Issue number6
ISSN2476-0455
DOIs
Publication statusPublished - Jun 2021

Bibliographical note

Funding Information:
This work is part of the project RiDILiq, which is funded by the Independent Research Fund, Denmark.

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