Surface segregation in binary mixtures of imidazolium-based ionic liquids |
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Authors: | Ryutaro Souda |
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Affiliation: | International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan |
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Abstract: | Surface composition of binary mixtures of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry at room temperature over a wide composition range. The imidazolium cations with longer aliphatic groups tend to segregate to the surface, and a bis(trifluoromethanesulfonyl)imide anion (Tf2N?) is enriched at the surface relative to hexafluorophosphate (PF6?). The surface of an equimolar mixture of Li[Tf2N] and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) has a nominal composition of [bmim][Tf2N] because of surface segregation and ligand exchange. The surface segregation of cations and anions is likely to result from alignment of specific ligand-exchanged molecules at the topmost surface layer to exclude more hydrophobic part of the molecules. |
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