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

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][Tf2N] (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 [C2C1IM][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][Tf2N] and [Me(EG)(3)MIm][Tf2N].