| 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 dielectricpermittivity up to 20 GHz of ionic liquids. The salts are comprised of pyrrolidinium, pyridinium,tetraalkylammonium, and triethylsulfonium cations combined with the bis-((trifluoromethyl)sulfonyl)imideanion. 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 supercooledand glassy systems rather than that observed in fluid systems. There is evidence for a weak secondary processnear 10−20 ps. Perhaps the most interesting difference to imidazolium salts is founded in the missing portionsof the spectra due to processes beyond the upper cutoff frequency of 20 GHz. These are lower than thatobserved 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 εS ≅ 10−13, classifyingthese ILs as solvents of moderate polarity.
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