Several rheological studies of ionic liquids and ionic liquid crystals were performed to describe the measured low coefficients of friction (mu approximate to 0.02) in reciprocating sliding tests (cylinder-on-disc and ring-on-disc). The main mechanisms which are assumed to lead to low friction values are the chemical composition of the anion and the orientation of the molecules under shear. The ionic liquid crystals show strong non-Newtonian viscosity behavior and viscoelastic properties in the liquid crystalline phase. In addition, the viscosity depends on the molecule orientation, which can be influenced by shear. At the transition from the liquid crystalline to the isotropic phase a strong decrease of viscosity is observed

Tribological investigations on the macroscopic scale revealed that friction can be influenced in situ by applying electric potentials, if electrically conductive fluid such as an ionic liquid is used as a lubricant. Enrichment of charged ions at a steel interface occurs by applying electric surface potentials in a three-electrode setup. As a consequence, the lubrication conditions change. It is supposed that electrically influenced surface adsorption and electrokinetic effects are the main mechanisms by which friction is varied.

In this work, a fundamental study of ionic liquids (ILs) is shown. The main goal was to establish relationships between rheological and tribological properties of ILs and to understand how these properties are linked to the molecular structure of ILs. Of particular interest were the effects occurring to a frictional system due to variations of the anions and the alkyl chain length of the imidazolium-based cations. Tribological experiments were performed using a reciprocating ball-on-disc test machine. To understand the effects resulting from a variation of the structural characteristics of the used ILs on the rheological properties, studies were performed using a rheometer. The results obtained are very promising in terms of improving friction and wear behaviour by using ILs as lubricants

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