The pressure-viscosity coefficient of several ionic liquids

The choice of cation and anion in an ionic liquid (IL) as well as the design of ion side chains determine the fundamental properties of ILs, which permits creating tailor-made lubricants and lubricant additives. So, the study of the influence of molecular structure on thermophysical properties of ionic liquids is essential for their use in lubrication. Recent results from the literature, essentially based on ammonium, phosphonium, or imidazolium cations, are promising from the tribological point of view, but still new investigations should be performed, for example, in elastohydrodynamic lubrication (EHL), for which calculations of the universal pressure-viscosity coefficient, alpha (film) , and central thickness are needed. In this work viscosity and density data from the literature on broad pressure and temperature ranges for the ILs [C(4)C(1)im]PF6, [C(4)C(1)im]Tf-2 N, [C(4)C(1)im]BF4, [C(8)C(1)im]PF6, [C(8)C(1)im]BF4, [C(6)C(1)im]PF6, and [C(6)C(1)im]Tf-2 N are used to determine their alpha (film) values over a wide temperature range. The American Gear Manufacturers Association relation of the central thickness with the pressure viscosity coefficient is used to estimate the film-generating capability of these lubricants. Furthermore, an overview of the literature data on tribological and physical properties of the ionic liquids is presented.