Influence of Different Substituents on the Surface Composition of Ionic Liquids Studied Using ARXPS

Abstract

Angle resolved X-ray photoelectron spectroscopy has been used to study the surface composition of various nonfunctionalized and functionalized 1,3-dialkylimidazolium ionic liquids. For [C n C 1 Im][Tf 2 N] (where n = 2−16), an enrichment of the aliphatic carbon was observed for longer chains ( n ≥ 4). Enrichment of the aliphatic carbon also occurs for alkyl chains attached to the anion, as observed for [C 2 C 1 Im][OcOSO 3 ]. Oligo(ethyleneglycol)ether (PEG) functionalities in the cation lead to a surface composition close to bulk stoichiometry and thus a loss in enrichment of the chains. This effect is attributed to attractive interactions between the oxygen atoms on the cation to the hydrogen atoms on the imidazolium ring for [Et(EG) 2 MIm][Tf 2 N] and [Me(EG) 3 MIm][Tf 2 N].