Surface Characterization of Functionalized Imidazolium-Based Ionic Liquids

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• 作者：Claudia Kolbeck ; Manuela Killian ; Florian Maier ; Natalia Paape ; Peter Wasserscheid ; Hans-Peter Steinrü ; ck
• 刊名：Langmuir
• 出版年：2008
• 出版时间：September 2, 2008
• 年：2008
• 卷：24
• 期：17
• 页码：9500-9507
• 全文大小：320K
• 年卷期：v.24,no.17(September 2, 2008)
• ISSN：1520-5827

文摘

The surface composition of oligo(ethylene glycol) ether functionalized bis(trifluoromethylsulfonyl)imide ionic liquids has been studied by means of X-ray photoelectron spectroscopy (XPS). For [Me(EG)MIM][Tf<sub>2sub>N], [Et(EG)<sub>2sub>MIM][Tf<sub>2sub>N], and [Me(EG)<sub>3sub>MIM][Tf<sub>2sub>N], which vary by the number of ethylene glycol (EG) units (from 1 to 3), we have shown that the stoichiometry of the surface near region is in excellent agreement with the bulk stoichiometry, which confirms the high purity of the ionic liquid samples investigated and rules out pronounced surface orientation effects. This has been deduced from the experimental observation that the angle-resolved XP spectra of all elements present in the IL anions and cations (C, N, O, F, S) show identical signals in the bulk and surfaces sensitive geometry, i.e., at 0° and 70° emission angle, respectively. The relative intensity ratios of all elements were found to be in nearly perfect agreement with the nominal values for the individual ILs. In contrast to these findings, we identified surface-active impurities in [Me(EG)MIM]I, which is the starting material for the final anion exchange step to synthesize [Me(EG)MIM][Tf<sub>2sub>N]. Sputtering of the surface led to a depletion of this layer, which however recovered with time. The buildup of this contamination is attributed to a surface enrichment of a minor bulk contamination that shows surface activity in the iodide melt.