Abstract
We present large scale polarizable simulations of mixtures of the ionic liquids 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-ethyl-3-methylimidazolium dicyanamide with water, where the dielectric spectra, the ion hydration and the conductivity were evaluated. The dielectric decrement, the depression of the dielectric constant of water upon addition of ions, is found to follow a universal functional of Langevin type. Only three physical properties need to be known to describe the complete range of possible concentrations, namely the dielectric constant of pure water, of pure ionic liquid and the linear slope of the dielectric decrement at low ionic liquid concentrations. Both the generalized dielectric constant, as well as the water contribution to the dielectric permittivity follow the functional dependence. We furthermore find that a scaling of van der Waals parameters upon addition of polarizable forces to the force field is necessary to correctly describe the frequency dependent dielectric conductivity and its contribution to the dielectric spectrum, as well as the static electric conductivity, which is also treated in the framework of a pseudolattice theory.
Highlights
We present large scale polarizable simulations of mixtures of the ionic liquids 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-ethyl-3-methylimidazolium dicyanamide with water, where the dielectric spectra, the ion hydration and the conductivity were evaluated
We find that a universal Langevin functional, taking into account the static dielectric constant of pure water and ionic liquid, as well as the initial slope of the dielectric decrement at low concentrations is capable of describing the dielectric decrement
The static dielectric constant at the zero frequency limit diminished upon addition of ionic liquid to water, in agreement with the theory of the dielectric decrement
Summary
Dielectric relaxation spectroscopy (DRS) of ionic solutions opens up the possibility of quantifying ion–ion and ion–solvent interactions.[15]. Levy et al investigated interactions of water dipoles in the vicinity of ions by a static dipolar Poisson–Boltzmann approach.[34] They were able to reproduce the dielectric decrement up to ion concentrations of 5 M. Their model was successful for our non-polarizable aqueous 1-butyl-3-methylimidazolium tetrafluoroborate mixtures.[28]. This study contributes to the understanding of the dielectric decrement in ionic liquid/water mixtures, and the extent to which atomic ion model theories apply to molecular ions. We calculate the corrected universal conductivity parabola of the electric conductivity, interrogating the pseudolattice model for the conductivity of ionic liquids.[2,4]
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