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Surface Enrichment in Equimolar Mixtures of Non-Functionalized and Functionalized Imidazolium-Based Ionic Liquids

Surface Enrichment in Equimolar Mixtures of Non-Functionalized and Functionalized Imidazolium-Based Ionic Liquids

Bettina S J Heller, Claudia Kolbeck, Inga Niedermaier, Sabine Dommer, Jürgen Schatz, Patricia Hunt, Florian Maier, Hans-Peter Steinrück

Chemphyschem. 2018 Jul 17;19(14):1733-1745.

PMID: 29645340

Abstract:

For equimolar mixtures of ionic liquids with imidazolium-based cations of very different electronic structure, we observe very pronounced surface enrichment effects by angle-resolved X-ray photoelectron spectroscopy (XPS). For a mixture with the same anion, that is, 1-methyl-3-octylimidazolium hexafluorophosphate+1,3-di(methoxy)imidazolium hexafluorophosphate ([C8 C1 Im][PF6 ]+[(MeO)2 Im][PF6 ]), we find a strong enrichment of the octyl chain-containing [C8 C1 Im]+ cation and a corresponding depletion of the [(MeO)2 Im]+ cation in the topmost layer. For a mixture with different cations and anions, that is, [C8 C1 Im][Tf2 N]+[(MeO)2 Im][PF6 ], we find both surface enrichment of the [C8 C1 Im]+ cation and the [Tf2 N]- (bis[(trifluoromethyl)sulfonyl]imide) anion, while [(MeO)2 Im]+ and [PF6 ]- are depleted from the surface. We propose that the observed behavior in these mixtures is due to a lowering of the surface tension by the enriched components. Interestingly, we observe pronounced differences in the chemical shifts of the imidazolium ring signals of the [(MeO)2 Im]+ cations as compared to the non-functionalized cations. Calculations of the electronic structure and the intramolecular partial charge distribution of the cations contribute to interpreting these shifts for the two different cations.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP304680362	1-Methyl-3-octylimidazolium hexafluorophosphate		304680-36-2	Price

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