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On the interfacial behavior of ionic liquids: Surface tensions and contact angles

Journal of Colloid and Interface Science
Publication Date
DOI: 10.1016/j.jcis.2009.08.013
  • Ionic Liquids
  • Surface Tension
  • Contact Angles
  • Polarity


Abstract In this work the liquid/vapour and the solid/liquid interfaces of a series of ionic liquids: 1-ethyl-3-methylpyridinium ethyl sulfate, [EMPy][EtSO 4], 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM][EtSO 4] , 1-ethanol-3-methylimidazolium tetrafluoroborate, [C 2OHMIM][BF 4], 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF 4], and 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIM][BF 4], were investigated. The surface tension was measured in a wide temperature range, (298–453) K. The contact angles were determined on substrates of different polarities. Both on the polar (glass) and the non-polar substrates ((poly-(tetrafluoroethylene) and poly-(ethylene)), the liquids with maximum and minimum surface tensions lead, respectively, to the highest and the lowest contact angles. The dispersive, γ L d , and non-dispersive, γ L nd , components of the liquid surface tension, γ L , were calculated from the contact angles on the non-polar substrates using the Fowkes approach. The polarity fraction, γ L nd / γ L , was compared with the polarity parameter, k, obtained from the fitting of the surface tension vs. temperature data to the Eötvös equation. Good agreement was found for the extreme cases: [OMIM][BF 4] exhibits the lowest polarity and [BMIM][BF 4], the highest. When compared with the polarity fractions of standard liquids considered as “polar” liquids, the ionic liquids studied may be considered as moderately polar.

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