(190n) Viscosity Modeling of Ionic Liquids Using the Friction Theory

In this work, the f-theory model [1] based on friction concepts of classical mechanics and the van de Waals theory of fluids has been extended to the accurate correlation and/or prediction of the dynamic viscosity of pure ionic liquids. Within the f-theory framework the dilute gas limit for viscosity was neglected since it is not relevant for ionic liquids exhibiting immeasurably low vapor pressures; the friction term thus prevailed for viscosity calculations. The latter was expressed in terms of three temperature-dependent friction coefficients along with repulsive and attractive pressure terms of the van der Waals type which in turn were computed from two simple cubic equations of state: Soave or Peng-Robinson. The resulting model was successfully validated during the representation of experimental dynamic viscosities of various imidazolium- and pyridinium-based ionic liquids within a wide temperature range and at moderate pressures. Model viscosity predictions at much higher pressures were also verified.

[1] Quiñones-Cisneros, S.E., Zéberg-Mikkelsen, C.K., Stenby, E.H., Fluid Phase Equilibria, 169, 249-276 (2000).