Tribological Performance of Cyano-Based Ionic Liquids as Functional Fluid

Ionic liquids (ILs) are expected to function as novel lubricants because of their superior properties compared to conventional lubricants. Although halogen-based ILs exhibit excellent tribological performance, they also cause corrosion of worn surfaces; thus, alternative ILs are required. To this end, cyano-based ILs have been investigated as functional lubricants that can reduce the environmental burden which other lubricants may cause. However, compared to conventional ILs, the tribological performance of cyano-based ILs was poor. However, their performance improved considerably when the chemistry of the sliding surface was changed. In addition, ultralow friction was obtained when the cyano-based ILs were used in conjunction with diamond-like carbon (DLC) films as the sliding surface. Overall, the results indicate that both the IL structure and the nature of the sliding materials must be carefully considered when cyano-based ILs are used as lubricants.