Interpretation of the Variation of the Walden Product of Ionic Liquids with Different Alkyl Chain Lengths in Terms of Relaxation Spectra

Abstract

The shear relaxation spectra and the alternating-current (AC) conductivity of 1-alkyl-3-methylimidazolium hexafluorophosphate were measured in the MHz region, with the chain lengths varied from butyl to octyl. The relaxation times of both the conductivity and shear viscosity increased with increasing chain length approximately in proportion to the variation of the reciprocal molar conductivity. On the other hand, the increase in the shear viscosity was smaller than that of the relaxation time, which indicates that the high-frequency shear modulus decreases with the chain length. The decrease in the the Walden product with the chain length is thus ascribed to that of the high-frequency shear modulus.

Shear Thinning and Nonlinear Structural Deformation of Ionic Liquids with Long Alkyl Chains Studied by Molecular Dynamics Simulation

“…The higher |η*(ω)| in the high-frequency region means the larger plateau modulus of [emim][TFSA], which is ascribed to larger ionic density. 16,17 The similar inversion is also observed in η(γ) at γ̇> 0.01 ps −1 , which suggests that the viscosity under high-shear rate reflects the strength of the instantaneous intermolecular interaction rather than the relaxation dynamics of microscopic structures.…”

“…Comparing frequency-dependent linear viscosities, |η*­(ω)|, of [emim]­[TFSA] and [omim]­[TFSA] at fixed angular frequency, although |η*­(ω)| of the former is smaller than that of the latter at ω < 0.1 ps –1 , the relation is inverted at higher ω. The higher |η*­(ω)| in the high-frequency region means the larger plateau modulus of [emim]­[TFSA], which is ascribed to larger ionic density. , The similar inversion is also observed in η­(γ̇) at γ̇ > 0.01 ps –1 , which suggests that the viscosity under high-shear rate reflects the strength of the instantaneous intermolecular interaction rather than the relaxation dynamics of microscopic structures.…”

Understanding the thermal and dielectric response of organosolv and modified kraft lignin as a carbon fibre precursor

“…For this reason, several correlations between measured conductivity and other processing parameters, such as viscosity have been established. [41][42][43][44][45] To facilitate the interpretation of results, in Figure 14 approx. However, for the ML sample, a nearly temperature independent conductivity in the initial mixture from 160ºC is a result of the commensurate effect of temperature on intrinsic conductivity (which probably decreases with increasing temperature as the hydrogenbonding intensity does) and extrinsic conductivity (which increases with increasing temperature).…”

Microstructural and Dynamical Heterogeneities in Ionic Liquids

“…In addition, [N 1, n,n,n ]­[NTF 2 ] ILs are not very viscous, but they exhibit a (low-frequency) macroscopic solidlike response to a low shear strain even at 100 °C above the glass transition temperature, indicating collective elastic intermolecular interactions and long relaxation time scales. Therefore, the role of shear elasticity has to be considered for a better understanding of their odd properties, such as a non-Arrhenius temperature dependence of viscosities and ion conductivities as well as deviations of these dynamical properties from the Nernst–Einstein equation and their variations in the Walden plot, which are intrinsically ascribed to changes in high-frequency shear modulus with lengthening alkyl chains in tetraalkylammonium cations …”