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

Journal Article · · Journal of Physical Chemistry. B
 [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)

Multinuclear (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. In addition, 2H T1 data suggest increased ordering with increasing pressure, with two T1 regimes observed for the MD3 and D2 isotopologues between 0.1–100 and 100–250 MPa, respectively. As a result, the activation volumes for T1 were 21 and 25 cm3/mol (0–100 MPa) and 11 and 12 cm3/mol (100–250 MPa) for the MD3 and D2 isotopologues, respectively.

Research Organization:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC00112704
OSTI ID:
1222605
Alternate ID(s):
OSTI ID: 1226072
Report Number(s):
BNL-108392-2015-JA; BNL-108556-2015-JA; R&D Project: CO-031; KC0301010
Journal Information:
Journal of Physical Chemistry. B, Journal Name: Journal of Physical Chemistry. B; ISSN 1520-6106
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 31 works
Citation information provided by
Web of Science

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Cited By (3)

Microscopic Structural and Dynamic Features in Triphilic Room Temperature Ionic Liquids journal May 2019
Communication: Investigation of ion aggregation in ionic liquids and their solutions with lithium salt under high pressure journal January 2018
Structural analysis of ionic liquids with symmetric and asymmetric fluorinated anions journal August 2019

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