Relationship between structure and tribological properties of ionic liquids composed of imidazolium cations

Tribological properties of ionic liquids were evaluated by pendulum and ball on disk tribotesters. Imidazolium cations with different alkyl chain length were used as a lubricant. It was found that friction coefficient decreased with increasing alkyl chain length. Among the ionic liquids examined in the present work, dodecylmethylimidazorium bis(trifluoromethanesulfonyl)imide reduced friction and wear remarkably. Surface analyses of wear track by X-ray Photoelectron Spectroscopy and Time of Flight Secondary Ion Mass Spectroscopy revealed that anions reacted with steel surface and that metal fluoride and sulfate were formed in the wear track. From the results, it can be concluded that the reaction products and chemisorbed cations affected the tribological behavior of the ionic liquids.