Surface characterization of functionalized imidazolium-based ionic liquids.
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 2N], [Et(EG) 2MIM][Tf 2N], and [Me(EG) 3MIM][Tf 2N], 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 degrees and 70 degrees 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 2N]. 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.
Kolbeck
Claudia
C
Lehrstuhl fur Physikalische Chemie II, Department Chemie and Pharmazie, Friedrich-Alexander-Universitat Erlangen-Nurnberg, Egerlandstrasse 3, 91058 Erlangen, Germany.
Killian
Manuela
M
Maier
Florian
F
Paape
Natalia
N
Wasserscheid
Peter
P
Steinrück
Hans-Peter
HP
D000838:Anions; D002412:Cations; D002627:Chemistry, Physical / Q000379:methods; D019855:Ethylene Glycol / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry*; D007094:Imides / Q000737:chemistry; D007454:Iodides / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry*; D007477:Ions; D008956:Models, Chemical; D015394:Molecular Structure; D011092:Polyethylene Glycols / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D014466:Ultraviolet Rays
D000838:Anions; D002412:Cations; D007093:Imidazoles; D007094:Imides; D007454:Iodides; D052578:Ionic Liquids; D007477:Ions; D011092:Polyethylene Glycols; D019855:Ethylene Glycol