High correlate simple equations for temperature and pressure dependence of the viscosity of ionic liquids

In this work, a new simple linear equation was proposed to represent the pressure dependence of the viscosity of ionic liquids. Literature experimental viscosity data were utilized and correlated as a function of pressure. The viscosity data of various ionic liquids including imidazolium, pyridinium, pyrrolidinium, and ammonium with a variety of anions were considered to examine the generality of the proposed equation. We showed that this equation provides accurate descriptions of the viscosity of ionic liquids as a function of pressure. Therefore, the proposed linear equation combines simplicity and accuracy. In addition, a new equation was proposed to incorporate both the temperature and pressure dependence of the viscosity (eta-T-p). The results indicated that the eta-T-p model shows high accuracy with an overall average absolute relative deviation of 2.69% in the temperature range of 283.15-363.15 K and the pressure range of 0.06-300 MPa. Moreover, we analyzed the pressure-viscosity coefficient, which quantifies the effect of pressure on the fluid's viscosity. The calculated pressure-viscosity coefficient was found to increase with increasing alkyl chain length of the cation.