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Title: Do TFSA anions slither? Pressure exposes the role of TFSA conformational exchange in self-diffusion

Multi-nuclear (1H, 2H, and 19F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent 2H T1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, as shown by their respective activation volumes (28.8 ± 2.5 cm³/mol for TFSA vs. 14.6 ± 1.3 cm³/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis.
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [3] ;  [4] ;  [2]
  1. Brooklyn College, Brooklyn, NY (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Hunter College, New York, NY (United States)
  4. City Univ. Graduate School (CUNY), NY, New York (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
OSTI Identifier:
1222605
Report Number(s):
BNL--108392-2015-JA
Journal ID: ISSN 1520-6106; R&D Project: CO-031; KC0301010
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
Additional Journal Information:
Journal Name: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry; Journal ID: ISSN 1520-6106
Publisher:
American Chemical Society
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY ionic liquids; diffusion