Diffusion of imidazolium based ionic liquids in different polar solvents
Eliane Schmidt
The solvation behaviour of ionic liquids in different solvents is very important for industrial applications. Solvent-solute-properties can be observed by their binary diffusion coefficients which can be measured by the fast and accurate Taylor dispersion technique.
Here, using the Taylor dispersion technique, we present diffusion coefficients of the ionic liquids [C2MIM][EtSO4], [C4MIM][OcSO4], [C2MIM][NTf2] and [C4MIM][NTf2] in water [1], methanol and acetonitrile in a temperature range between 288 K and 313 K. Furthermore we calculated the activation energies and the prefactors of the Arrhenius plots and show that the temperature dependence of the diffusion is characteristic for the solvents.
In order to support our experimental results we also present MD simulations of [C2MIM][NTf2] and [C4MIM][NTf2] in water, methanol and acetonitrile using the force field parameters of the imidazolium-based ionic liquids from T. Köddermann [2]. With the help of this method we are able to calculate binary diffusion coefficients via self diffusion coefficients and the comparison between the simulated and the measured values is very good. The advantage of MD is the molecular view into the solutions. We show that depending on the solvent the solution contains neutral aggregates of ion pairs and solvated ions as diffusive species.
References
- Heintz A., Lehmann J. K., Schmidt E., Wandschneider A. J. Solution Chem. 38, 1079 – 1083 (2009).
- Köddermann T., Paschek D., Ludwig R. ChemPhysChem 8, 2464 - 2470 (2007).