Molecular dynamics simulations of ionic liquids: Cation and anion dependence of self-diffusion coefficients of ions

Seiji Tsuzuki, Wataru Shinoda, Hiroaki Saito, Masuhiro Mikami, Hiroyuki Tokuda, Masayoshi Watanabe

Research output: Contribution to journalArticlepeer-review

202 Citations (Scopus)

Abstract

Molecular dynamics simulations of a series of ionic liquids [1-alkyl-3-methylimidazolium (alkyl) methyl, ethyl, butyl, hexyl, and octyl), 1-butylpyridinium, N-butyl-N, N, N-trimethylammonium and N-butyl-N- methylpyrrolidinium cations combined with a (CF3SO2) 2N- anion ([mmim][TFSA], [emim][TFSA], [bmim][TFSA], [C6mim][TFSA], [C8mim][TFSA], [bpy][TFSA], [(n-C 4H9)(CH3)3N][TFSA], and [bmpro][TFSA]) and a 1-butyl-3-methylimidazolium combined with BF 4-, PF6-, CF3CO 2-, CF3SO3-, and (C 2F5SO2)2N- anions ([bmim][BF4], [bmim][PF6], [bmim][CF3CO 2], [bmim][CF3SO3], and [bmim][BETA])] were carried out using the OPLS force field for ionic liquids. The force field was refined on the basis of ab initio molecular orbital calculations of isolated ions and experimental densities for four ionic liquids. The densities calculated for the 13 ionic liquids agreed with the experimental values within a 2% error. The self-diffusion coefficients calculated for the ions in the 13 ionic liquids were compared with the experimental values obtained by the NMR measurements. Although the calculated self-diffusion coefficients were about 1 order smaller than the experimental ones, the cation and anion dependence (the effects of alkyl chain length in imidazolium, cation structures, and anion species) of the experimental self-diffusion coefficients was reproduced by the simulations quite well in most cases. The translational motion of the terminal carbon atoms in the alkyl chains of the imidazolium cations on the time scale of a few nanoseconds is significantly faster than that of the atoms in the imidazolium rings and anions, which suggests that the dynamics of atoms in the polar domains of the ionic liquids is significantly different from that in the nonpolar domains. The factors determining the self-diffusion coefficients of the ions are also discussed.

Original languageEnglish
Pages (from-to)10641-10649
Number of pages9
JournalJournal of Physical Chemistry B
Volume113
Issue number31
DOIs
Publication statusPublished - Aug 6 2009
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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