Investigation of the rheological properties of two imidazolium-based ionic liquids

Abstract

The shear- and temperature-dependency of the viscosity of two imidazolium-based ionic liquids namely, 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6] and 1-butyl-3-methylimidazolium nitrate, [bmim][NO3], has been studied in this work. The experimental results showed that the viscosity of these fluids decreases with increasing temperature. The results also showed that these ionic liquids are non-Newtonian over a wide range of shear rate ((14 to 56.0) s−1) in the temperature range of (283.15 to 343.15) K and their shear viscosity depends strongly on temperature. The activation parameters, namely, ΔH⁎ (enthalpy of activation), ΔG⁎ (free energy of activation), ΔS⁎ (entropy of activation), and ΔCp⁎ (change in heat capacity of activation) values for their viscous flow were evaluated. The magnitudes of the parameters were fairly large. The values of all these parameters decreased with temperature. The values of ΔH⁎ and ΔS⁎ nicely compensated each other. The temperature dependence of viscosities was fitted using the power law, Litovitz, Vogel–Fulcher–Tammann (VFT), and Ghatee et al. equations. Also, the law of corresponding states can be seen in the viscosity behavior of these ILs based on two different equations.