Perfect Composition Depth Profiling of Ionic Liquid Surfaces Using High-resolution RBS/ERDA

Abstract

In order to reveal the surface structures of large molecular ionic liquids (ILs), the near-surface elemental depth distributions of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CnC1Im][Tf2N], n = 2, 6, 10) were studied using high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with high-resolution elastic recoil detection analysis (HR-ERDA). The elemental depth profiles of all constituent elements, including hydrogen, were derived from HR-ERDA/HRBS measurements, so that the profiles would reproduce both HR-ERDA and HRBS spectra simultaneously. The derived elemental depth profiles agree with state-of-the-art molecular dynamics simulations, indicating the feasibility of this method. A controversy concerning the preferential orientation of [C2C1Im] at the surface has been resolved by this new combination analysis; namely, the [C2C1Im] cation has a preferential orientation with the ethyl chain pointing towards the vacuum in the topmost molecular layer.

On the adsorption of n-butane on alkyl imidazolium ionic liquids with different anions using a new molecular beam setup

“…[47][48][49] Since 2005/2006, ILs are in the focus of surface science studies, and this new field of "ionic liquid surface science" 50 has developed a detailed understanding of the steady state or static properties of the vacuum/IL interface, such as surface composition, surface enrichment, and orientation effects. 30,31,[33][34][35][36]51,52 For specific systems, even chemical reactions in ionic liquids have been studied (see Ref. 53 and references therein).…”

Ionic Liquids as Liquid Materials for Analytical Chemistry

“…Ionic liquids (ILs) are attracting liquid media for analytical chemistry due to their several fascinating characteristics, such as negligible vapor pressure, chemical and electrochemical stability, and a unique ionic solvation environment. ILs have been studied in a vast area of analytical chemistry research fields 1,2 such as chromatography, 3-5 extraction, 5-11 optical 12,13 and electrochemical [14][15][16][17] sensing, and interfacial 18,19 and bulk liquid 20,21 analysis.…”