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.

Mass and charge transport in 1-alkyl-3-methylimidazolium triflate ionic liquids

“…[13][14][15] However, Hunger et al have demonstrated that an Onsager-type equation adequately characterizes the temperature dependence of the static dielectric constant for a variety of ionic liquids. 10 Additionally, it is well-known that Onsager's equation is only applicable to aprotic liquids 16 and controversy exists about whether the imidazolium cation undergoes hydrogen bonding interactions.…”

Analysis of the Influence of Dielectric Polarization on the Study of Electronic Orientation of Electromagnetic Field Propagating Through Oxide Based Thin Film

“…The problem involved in ordering effect of the field energy and the disordering influence of thermal energy is such that each molecule with a permanent dipole moment µ makes a contribution to the polarization proportional to the field. [4]. However, Langevin idea that said that the dipole must be aligned completely in order to achieve saturation value failed to consider dipole-dipole interaction [5] (i.e., he neglected Eµ) and hence the expression he obtained for polarization cannot be used without modification when such an interaction in magnetic field is significant especially as it is caused by induced dipoles, which gives rise to dispersions.…”

Terahertz dynamics of ionic liquids from a combined dielectric relaxation, terahertz, and optical Kerr effect study: evidence for mesoscopic aggregation

“…Raman and optical Kerr-effect (OKE) spectroscopy have been able to access the relatively high frequency region from ~0.1 to 10 THz. [26][27][28] The sub-THz region, corresponding to intermolecular modes, has been investigated by terahertz time-domain spectroscopy [29,30], dielectric relaxation spectroscopy (DRS) [31][32][33][34][35][36][37], and OKE spectroscopy [3,5,26,[38][39][40][41][42][43][44][45]. In general, DRS is limited to a maximum frequency of about 100 GHz whereas the spectra of most RTILs are continuous up to several THz.…”