title: Surface layering in ionic liquids: an X-ray reflectivity study.
abstract: The surface structure and thermodynamics of two ionic liquids, based on the 1-alkyl-3-methylimidazolium cations, were studied by X-ray reflectivity and surface tensiometry. A molecular layer of a density approximately 18% higher than that of the bulk is found to form at the free surface of these liquids. In common with surface layering in liquid metals and surface freezing in melts of organic chain molecules, this effect is induced by the lower dimensionality of the surface. The concentrations of the oppositely charged ions within the surface layer are determined by chemical substitution of the anion. The temperature-dependent surface tension measurements reveal a normal, negative-slope temperature dependence. The different possible molecular arrangements within the enhanced-density surface layer are discussed.
authors.affiliation: Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors.forename: Eli
authors.initials: E
authors.lastname: Sloutskin
authors.forename: Eli
authors.initials: E
authors.lastname: Solutskin
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Ocko
authors.forename: Lilach
authors.initials: L
authors.lastname: Tamam
authors.forename: Lilach
authors.initials: L
authors.lastname: Taman
authors.forename: Ivan
authors.initials: I
authors.lastname: Kuzmenko
authors.forename: Thomas
authors.initials: T
authors.lastname: Gog
authors.forename: Moshe
authors.initials: M
authors.lastname: Deutsch