Ionic conductivity of deep eutectic solvents: the role of orientational dynamics and glassy freezing

Abstract

We have performed a thorough examination of the reorientational relaxation dynamics and the ionic charge transport of three typical deep eutectic solvents, ethaline, glyceline and reline by broadband dielectric spectroscopy. Our experiments cover a broad temperature range from the low-viscosity liquid down to the deeply supercooled state, allowing to investigate the significant influence of glassy freezing on the ionic charge transport in these systems. In addition, we provide evidence for a close coupling of the ionic conductivity in these materials to reorientational dipolar motions which should be considered when searching for deep eutectic solvents optimized for electrochemical applications. __________________________________________________________________ DSC resultsFig. S1 DSC results on the three DESs treated in the present work as obtained under heating with 10 K/min.

Electron Transfer Kinetics in a Deep Eutectic Solvent

“…7 The relaxation times  L are derived from dielectric loss measured by dielectric spectroscopy techniques. 38,39 Several studies were dedicated to ionic liquids (see for example 40 for investigation of imidazolium-based ionic salts and reference used for Table S1 in SI) but Ethaline was only recently investigated by dielectric spectroscopy in a wide range of frequencies and temperatures. 38 Authors have observed that a single relaxation time describes the reorientational dipolar motions for Ethaline with times close to those of the molecular component.…”

“…38,39 Several studies were dedicated to ionic liquids (see for example 40 for investigation of imidazolium-based ionic salts and reference used for Table S1 in SI) but Ethaline was only recently investigated by dielectric spectroscopy in a wide range of frequencies and temperatures. 38 Authors have observed that a single relaxation time describes the reorientational dipolar motions for Ethaline with times close to those of the molecular component. 38,39 Relaxation times were fitted using a VFT law (Vogel-Fulcher-Tammann) in the whole range of investigated temperatures.…”

Deep Eutectic Solvents for Pretreatment, Extraction, and Catalysis of Biomass and Food Waste

“…Dielectric relaxation spectroscopy (DRS) is known to be a useful technique to investigate the structural dynamics of liquids [151]. Moreover, for materials of an ionic nature, dielectric spectroscopy is an effective method by which to understand the mechanisms related to charge transport [152]. Despite many studies on ILs, only a few studies on the dielectric properties of DESs have been performed [152,153,154,155,156,157,158,159].…”

“…Moreover, for materials of an ionic nature, dielectric spectroscopy is an effective method by which to understand the mechanisms related to charge transport [152]. Despite many studies on ILs, only a few studies on the dielectric properties of DESs have been performed [152,153,154,155,156,157,158,159]. For example, Griffin et al [159] utilized broadband dielectric spectroscopy in combination with depolarized dynamic light scattering to explore the charge transport and structural dynamics of a deep eutectic mixture, {Lidocaine:2Decanoic acid}.…”

“…Moreover, as for the ionic acetamide DESs, the non-ionic polyethylene-glycol-based DES has a nanosecond relaxation component. Very recently, Reuter et al [152] employed dielectric spectroscopy to study the reorientational relaxation dynamics and the charge transfer of three DESs, {ChCl:Ethylene glycol}, {ChCl:Urea} and {ChCl:Glycerol}, all at a 1:2 molar ratio. They found that the ionic translational motions and the reorientational motions were closely coupled.…”