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

• Densities and viscosities of (PEG200 + ionic liquids) solutions are measured.
• Imidazolium ionic liquids having bistrifllamide and triflate anions are studied.
• Several excess properties of the solutions are calculated and interactions analyzed.
• Stronger attractive interactions are provoked by ionic liquids with triflate anion.
• Importance of the excess Gibbs energy of activation of viscous flow pointed-out.

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 0.1 MPa and in the temperature range of 288.15–318.15 K, 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.