title: Temperature-dependent surface-enrichment effects of imidazolium-based ionic liquids.
abstract: We present the first systematic study of the influence of temperature on the degree of surface enrichment of 1-alkyl-3-methylimidazolium-based ionic liquids (ILs). Using angle-resolved X-ray photoelectron spectroscopy, we demonstrate that the degree of surface enrichment strongly decreases with increasing temperature for all the studied ILs. For ILs with the same cation, but different anions, [C8 C1 Im]Br, [C8 C1 Im][TfO] and [C8 C1 Im][Tf2 N], no significant differences of the temperature-induced partial loss of surface enrichment are found. Measurements for [C4 C1 Im][TfO], [C8 C1 Im][TfO] and [C18 C1 Im][TfO] indicate a small effect of the chain length. For [C18 C1 Im][TfO], a continuous decrease of alkyl surface enrichment is found with increasing temperature, with no abrupt changes at the phase-transition temperature from the smectic A to the isotropic phase, indicating that the surface enrichment is not affected by this phase transition.
authors.affiliation: Lehrstuhl für Physikalische Chemie, Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058 Erlangen (Germany), Fax: (+49) 9131-852886.
authors.forename: Claudia
authors.initials: C
authors.lastname: Kolbeck
authors.forename: Alexey
authors.initials: A
authors.lastname: Deyko
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuda
authors.forename: Florian T U
authors.initials: FT
authors.lastname: Kohler
authors.forename: Peter
authors.initials: P
authors.lastname: Wasserscheid
authors.forename: Florian
authors.initials: F
authors.lastname: Maier
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Steinrück
keywords: X-ray photoelectron spectroscopy (XPS); interfaces; ionic liquids; surface science; temperature dependence