In Silico Predictions of the Temperature-Dependent Viscosities and Electrical Conductivities of Functionalized and Nonfunctionalized Ionic Liquids

Abstract

The viscosity (η) and electrical conductivity (κ) of ionic liquids are, next to the melting point, the two key properties of general interest. The knowledge of temperature-dependent η and κ data before their first synthesis would permit a much more target-oriented development of ionic liquids. We present in this work a novel approach to predict the viscosity and electrical conductivity of an ionic liquid without further input of experimental data. For the viscosity, only some basic physical observables like the Gibbs solvation energy (ΔG(solv)(*,∞)), which was calculated at the affordable DFT-level (RI-)BP86/TZVP/COSMO, the molecular radius, calculated from the molecular volume V(m) of the ion volumes, and the symmetry number (σ), according to group theory, are necessary as input. The temperature dependency (253-373 K) of the viscosity (4-19000 mPa s) was modeled by an Arrhenius approach. An alternative way, which avoids the deficits of the Arrhenius relation by a series expansion in the exponential term, is also presented. On the basis of their close connection, the same set of parameters is suitable to describe the electrical conductivity as well (238-468 K, 0.003-193 mS/cm). Nevertheless, more elegant alternatives like the usage of the Stokes-Einstein/Nernst-Einstein relation or the Walden rule are highlighted in this work. During this investigation, we additionally found an approach to predict the dielectric constant ε* of an ionic liquid at 298 K by using V(m) and ΔG(solv)(*,∞) between ε* = 9 and 43.

[HMIM][Br9]: a Room-temperature Ionic Liquid Based on a Polybromide Anion

“…Normally, ionic liquids based on imidazolium cations show conductivities in the range of 1 to 10 mS cm −1 at 25 • C [18,19]. In line with this observation the compound under investigation also exhibits an exceptionally high conductivity of, e. g., 52.1 mS cm −1 at 25.6 • C. Like for other ILs the temperature dependence of the conductivity is well described by a VogelFulcher-Tammann behavior [18].…”

Establishing Consistent van der Waals Volumes of Polyatomic Ions from Crystal Structures

“…4 ]-based ILs with V m,scaled . [58] As seen in Figure 1 a, Equation (2) As a further test T dependent values of h were fitted according to Equation (3): [59] …”

“…These are unity for almost all ions with the exception of those with tetrahedral (s À = 12) and octahedral (s À = 24) symmetry. Compared to the originally used formula, [59] the molecular radius r m in the second term is replaced by the volume V i . It is calculated as the sum of the constituting ion volumes.…”

Temperature Dependence of the Viscosity and Conductivity of Mildly Functionalized and Non‐Functionalized [Tf2N]− Ionic Liquids

“…Several recent studies showed that this is possible, for example, for conductivity, viscosity, density, surface tension and refractive index. [22][23][24][25] In continuation of our earlier work on IL properties, [23,[26][27][28][29][30][31][32][33] this manuscript is devoted to promote a further understanding and prediction of the detailed temperature-dependent viscosities and conductivities of ILs. Therefore, we first review in some detail the fundamentals of viscosity and conductivity, since they are important for the discussions below.…”