Tribological Properties of Dicationic Imidazolium Ionic Liquids at High Temperature

Three kinds of dicationic imidazolium ionic liquids (ILs) linked with different carbon chains were synthesized. An SRV-IV type friction and wear tester was performed to evaluate the tribological properties of as-synthesized ILs at elevated temperatures from 50 ℃ to 350 ℃ and at a constant temperature of 250 ℃. The morphology and elemental composition of the wear scars were analyzed by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results indicate that, as compared with the friction and wear test at varied temperatures, the tests at a constant temperature of 250 ℃ are more effective in differentiating the tribological properties of dicationic imidazolium ILs at elevated temperatures. In the meantime, the dicationic imidazolium ILs linked with alkyl bridge possessed better friction-reducing and anti-wear abilities than those linked with polyethylene glycol, and decreasing length of the alkyl linking chain of the dicationic ILs can improve their tribological properties.