Rheological properties of {[bmim]PF6 + methanol} mixtures at different temperatures, shear rates and compositions

Abstract

In this work, the shear-, temperature- and composition-dependencies of the viscosity of binary mixtures of 1-butyl-3-methylimidazolium hexafluorophosphate with methanol {[bmim]PF6+methanol} have been studied. The results showed that adding alcohol causes a gradual change in the behavior of the mixtures from moderate non-Newtonian (in pure ionic liquid) to Newtonian (in pure alcohol) over a wide range of shear rate ((14 to 56.0)s−1) in the temperature range of (283.15 to 333.15)K. 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) for their viscous flow were evaluated. The values of ΔH⁎ and ΔS⁎ nicely compensated each other. The temperature and composition dependencies of viscosities have been fitted using proper equations. Also, the law of corresponding states can be seen in the viscosity behavior of these mixtures based on two different equations. The excess molar properties were calculated from the experimental data and the Redlich–Kister polynomial equation was used to fit these data. An artificial neural network (ANN) method has been developed to model simultaneously the shear-, temperature- and composition- dependencies of the viscosities of these mixtures.