Effect and mixing of counter anions at the surface of aqueous solution of imidazolium-based ionic liquids

Huihui Li, Yosuke Imai, Takanori Takiue, Hiroki Matsubara, Makoto Aratono

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


The purpose of this study was to find the primary factor determining the mixing of the counter anions of 1-alkyl-3-methylimidazolium-based ionic liquid (IL, CnmimX) at the air/water interface. First, the properties of the adsorbed films of the C10mimBr-C10mimBF4 mixtures were estimated by using the thermodynamic analysis of their surface tension data. The mole fraction of BF4- was lower in the adsorbed films than in the ideal state and the excess Gibbs energy of adsorption was negative, which was in marked contrast to those of the C6mimBr-C6mimBF4 mixtures. Meanwhile, the possibility of forming side-by-side ion pair of BF4- and imidazolium ring at the adsorbed films, as we found in the C6mimBr-C6mimBF4 system, was greatly reduced in the present case. These changes were mainly attributed to the reduction in the hydrogen-bonding interaction between BF4- and C10mim+, as the carbon number in the hydrophobic part of Cnmim+ was increased from 6 to 10. In addition, it was found that the values of excess Gibbs energy of adsorption were less negative in the C10mimBr-C10mimBF4 system than in the dodecyltrimethylammonium (C12TA)Br-C12TABF4 system, where the long-range Columbic interaction solely exists between the counter anions and surfactant cations. Thus, we concluded that the short-range hydrogen-bonding interaction played an essential role in the interfacial activity of ILs.

Original languageEnglish
Pages (from-to)26-32
Number of pages7
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Publication statusPublished - Jun 2013

All Science Journal Classification (ASJC) codes

  • Surfaces and Interfaces
  • Physical and Theoretical Chemistry
  • Colloid and Surface Chemistry


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