title: The dielectric response of room-temperature ionic liquids: effect of cation variation.
abstract: In continuation of recent work on the dielectric response of imidazolium-based ionic liquids (ILs) (J. Phys. Chem. B, 2006, 110, 12682), we report on the effect of cation variation on the frequency-dependent dielectric permittivity up to 20 GHz of ionic liquids. The salts are comprised of pyrrolidinium, pyridinium, tetraalkylammonium, and triethylsulfonium cations combined with the bis-((trifluoromethyl)sulfonyl)imide anion. The dielectric spectra resemble those observed for imidazolium salts with the same anion. In all cases, the major contribution results from a diffusive low-frequency response on the time scale of several 100 ps, which shows a broadly distributed kinetics similar to that of spatially heterogeneous states in supercooled and glassy systems rather than that observed in fluid systems. There is evidence for a weak secondary process near 10-20 ps. Perhaps the most interesting difference to imidazolium salts is founded in the missing portions of the spectra due to processes beyond the upper cutoff frequency of 20 GHz. These are lower than that observed for imidazolium-based salts and seem to vanish for tetraalkylammonium and triethylsulfonium salts. As for imidazolium salts, the extrapolated static dielectric constants are on the order of epsilon(S) congruent with 10-13, classifying these ILs as solvents of moderate polarity.
authors.affiliation: Physical Chemistry 2, Ruhr-University Bochum, D-44780 Bochum, Germany. hermann.weingaertner@rub.de
authors.forename: Hermann
authors.initials: H
authors.lastname: Weingärtner
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Sasisanker
authors.forename: Corinne
authors.initials: C
authors.lastname: Daguenet
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Dyson
authors.forename: Ingo
authors.initials: I
authors.lastname: Krossing
authors.forename: John M
authors.initials: JM
authors.lastname: Slattery
authors.forename: Thomas
authors.initials: T
authors.lastname: Schubert
mesh_terms: D002412:Cations / Q000737:chemistry; D004553:Electric Conductivity; D052578:Ionic Liquids / Q000737:chemistry*; D015394:Molecular Structure; D011725:Pyridines / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013449:Sulfonamides / Q000737:chemistry*; D013452:Sulfonium Compounds / Q000737:chemistry*; D013696:Temperature
chemical_list: D002412:Cations; D052578:Ionic Liquids; D011725:Pyridines; D011758:Pyrroles; D000644:Quaternary Ammonium Compounds; D013449:Sulfonamides; D013452:Sulfonium Compounds; C036565:triethylsulfonium