Rheological characterization of ionic liquids and ionic liquid crystals with promising tribological performance†
Several rheological studies of ionic liquids and ionic liquid crystals were performed to describe the measured low coefficients of friction (μ ≈ 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.