Issue 26, 2010

A comparison of fluoroalkyl-derivatized imidazolium:TFSI and alkyl-derivatized imidazolium:TFSI ionic liquids: a molecular dynamics simulation study

Abstract

Molecular dynamics simulations of fluoroalkyl-derivatized imidazolium:bis(trifluoromethylsulfonyl)imide (TFSI) room temperature ionic liquids (FADI-RTILs) with cations of the structure 1-F(CF2)n(CH2)2-3-methyl imidazolium have been performed and compared with simulations of alkyl-derivatized 1-H(CH2)n+2-3-methyl imidazolium analogs (ADI-RTILs). Simulations yield RTIL densities, viscosities and ionic conductivities for the FADI-RTILs and ADI-RTILs in reasonably good agreement with experimental data. Partial fluorination results in a larger increase in density than would be anticipated based upon the density difference between perfluoralkane and alkane melts. Similarly, the slowing down in dynamics upon partial fluorination is greater than would be expected based upon the increase in cation volume. Examination of cation–cation, anion–anion and cation–anion centers-of-mass radial distribution functions reveal remarkably little influence of partial fluorination on the spherically averaged intermolecular structure of the RTILs. Similarly, simulations reveal little change in tail conformations and the extent of tail–tail aggregation upon partial fluorination. The interaction of the TFSI anion with the positively charged imidazolium ring hydrogen and nitrogen atoms is also little influenced by partial fluorination. However, the partially fluorinated alkyl tail exhibits increased interaction with the TFSI anion due to the electron withdrawing character of the fluorinated groups. We believe this strong tail–anion electrostatic interaction largely accounts for the higher than expected density and slower than expected dynamics in the FADI-RTILs.

Graphical abstract: A comparison of fluoroalkyl-derivatized imidazolium:TFSI and alkyl-derivatized imidazolium:TFSI ionic liquids: a molecular dynamics simulation study

Article information

Article type
Paper
Submitted
21 Jan 2010
Accepted
12 Apr 2010
First published
19 May 2010

Phys. Chem. Chem. Phys., 2010,12, 7064-7076

A comparison of fluoroalkyl-derivatized imidazolium:TFSI and alkyl-derivatized imidazolium:TFSI ionic liquids: a molecular dynamics simulation study

G. D. Smith, O. Borodin, J. J. Magda, R. H. Boyd, Y. Wang, J. E. Bara, S. Miller, D. L. Gin and R. D. Noble, Phys. Chem. Chem. Phys., 2010, 12, 7064 DOI: 10.1039/C001387K

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