Dynamics of RTILs: A comparative dielectric and OKE study

Abstract

The dynamics of room-temperature ionic liquids (RTILs) were studied by investigating their dielectric relaxation (DR) and timeresolved optical Kerr-effect (OKE) spectra in the frequency range of ∼10 MHz to ∼20 THz. For the studied RTILs the OKE and DR spectra are dominated by a relaxation in the GHz region and extend to a relatively sharp band at around 10 THz. Whilst the first feature is mainly associated with the structural relaxation of the fluid through ion rotation (α relaxation), the second indicates the short-time limit of intermolecular dynamics. The rather featureless intermediate region is mainly associated with intermolecular vibrations that are strongly coupled to hindered rotations. In contrast to other RTILs, imidazolium salts show an additional sub-α relaxation which dominates the OKE signal and is indicative of the breathing motion of rather long-lived cages.Mixed with polar solvents RTILs were found to retain their ionic liquid-like character up to relatively high levels of dilution, but with the overall dynamics considerably speeded up. Below RTIL mole fractions of ∼0.2-0.4 these systems behave like conventional electrolyte solutions with more or less pronounced ion pairing.

Microglobule formation and a microscopic order parameter monitoring the phase transition of aqueous poly( N -isopropylacrylamide) solution

“…Spectra of the complex permittivity ε * (ν) of aqueous pNIPAm solutions at identical w were determined in the frequency range between 0.2 and 89 GHz using a vector network analyzer (VNA) (Agilent, E8364B) with open-ended coaxial-line probes (Agilent, 85070E-020/-050) and Aand E-band waveguide interferometers (Regensburg) [35]. The VNA instrument was calibrated with air, mercury, and water.…”

Hydration and self-aggregation of a neutral cosolute from dielectric relaxation spectroscopy and MD simulations: the case of 1,3-dimethylurea

“…At n r 50 GHz a frequency-domain reflectometer, based on Agilent 85070E-20 and 85070E-50 dielectric probes connected to an Agilent E8364B vector network analyzer (VNA) and an electronic calibration module (Agilent N4693B), was used. 33 A range of 60-89 GHz was covered using a waveguide interferometer. 34 For selected samples the reliability of the reflection measurements was additionally crosschecked with a 27-40 GHz variable-pathlength waveguide transmission cell hooked to the VNA.…”

Mesoscale Organization and Dynamics in Binary Ionic Liquid Mixtures

“…[11][12][13][14][15][16] Mesoscale organization has been used to qualitatively explain numerous experimental findings which imply spatially and temporally distinct regions within bulk ionic liquids. [11,[17][18][19][20][21][22][23][24][25][26] Recent studies suggest that the existence and dynamics of the aggregates in neat ionic liquids, associated with fluctuations of the polar and non-polar regions, correlate strongly with many of the physicochemical properties of ionic liquids including transport properties such as zero-shear viscosity, dc ionic conductivity, and static dielectric permittivity. [27][28][29][30][31][32] However, no efforts to exploit the mesoscale organization to design novel ionic liquids with unique physical and chemical properties have been reported.…”