Tribological properties of imidazolium-based ionic liquids and the influence of polarization

Ionic liquids (Ils) are low-melting salts composed entirely of ions, and many of them are liquids at room temperature [1]. By varying the combination of cations and anions, the properties of ionic liquids can be altered [2]. In lubricated rolling or sliding contacts, these fluids stabilize friction on a low level due to adsorption and tribochemical reaction with surfaces, and therefore prevent direct metallic contacts. In comparison to standard lubricants there are several principal differences that make Ils interesting for some special applications. For instance their chemical stability up to very high temperatures (300 °C or even higher), at which even high-performance lubricants cannot be used. Also their negligibly low vapor pressure makes Ils attractive for use in vacuum or in environments that have to be kept very clean. The miscibility with organic solvents or water is a key requirement for developing technical lubricants.