Title: Effect of an external electric field on the dynamics and intramolecular structures of ions in an ionic liquid

Abstract

Simulations of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in an external electric field have been performed using a Drude particle polarizable force field. The structure of the ions has been analyzed, with close attention paid to the configurations of the ions. The “charge arm” concept is used to explain certain changes of these configurations that would be difficult to rationalize otherwise, e.g., trans → cis isomerization of the bis(trifluoromethylsulfonyl)imide anion and extension of the alkyl chain of the cation. It has also been shown that the ions orient themselves so that their charge arms align with and stretch out along the field, and these effects occur at lower external electric field strengths than cause a change in the inherent diffusion of the ions. Here, the dynamics of the system parallel and perpendicular to the field were analyzed, and it was found that the applied field affected the diffusion normal to the field. This is explained as a secondary effect of a change in the ion cage formed by the surrounding counterions of a given ion in the ionic liquid. The breakdown of the ion cages was rationalized by correlating changes to the inherent diffusion of the ions with other changes tomore » the diffusion and bulk structure of the liquid, as well as considering the average forces on the ions compared to the force the ions would be expected to experience in an electric field. Parallel to the field, a drift was observed at every electric field studied. In electric fields with no changes to the ion cage structure, the relationship between the drift and electric field was found to be linear, becoming nonlinear as the ion cage structure breaks down.« less

Authors:

Clark, Ryan  ^[1];

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von Domaros, Michael  ^[2];

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McIntosh, Alastair J. S.  ^[1];

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Luzar, Alenka  ^[3];

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Kirchner, Barbara  ^[2];

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Welton, Tom  ^[1]

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+ Show Author Affiliations

1. Imperial College, London (United Kingdom)
2. Univ. of Bonn (Germany)
3. Virginia Commonwealth Univ., Richmond, VA (United States)

Publication Date:

2019-10-25

Research Org.:

Virginia Commonwealth Univ., Richmond, VA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1638250

Alternate Identifier(s):

OSTI ID: 1571837

Grant/Contract Number:  

SC0004406

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Chemical Physics

Additional Journal Information:

Journal Volume: 151; Journal Issue: 16; Journal ID: ISSN 0021-9606

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; electrostatics; isomerization; ionic liquids; polarizable force fields; Brownian motion; physical quantities; Drude oscillator