Environmentally friendly solutions of liquid poly(ethylene glycol) and imidazolium based ionic liquids with bistriflamide and triflate anions: Volumetric and viscosity studies

In this paper, densities and viscosities of the solutions of PEG200 with two imidazolium ionic liquids, 1-ethyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ([C₂mim][NTf₂]) and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([C₂mim][OTf]), at pressure 0.1MPa and in the temperature range of 288.15-318.15K, were measured. The experimental data were used to calculate excess molar volumes, deviations in viscosity and excess molar Gibbs free energies of activation of viscous flow for the studied solutions. Excess molar volumes indicate strong attractive interactions provoked by the studied ionic liquids which are even enhanced in the case of the [C₂mim][OTf] as a solution component. The analysis of the viscosity data showed that these cannot be solely explained on the basis of the interactions between the present molecules/ions and that the factors also related to entropy - size and packing of molecules - must be considered as well. Thus, excess molar Gibbs free energy of activation of viscous flow appeared as very important for a complete description of the current viscosity behavior.