Ultralow Friction and High Robustness of Monolayer Ionic Liquids

Ultralow friction between interacting surfaces in relative motion is of vital importance in many pure and applied sciences. We found that surfaces bearing ordered monolayer ionic liquids (ILs) can have friction coefficient mu values as low as 0.001 at pressures up to 78 MPa and exhibit good structure recoverability. This extreme lubrication is attributed primarily to the ordered striped structure driven by the atomic-locking effect between carbon atoms on the alkyl chain of ILs and graphite. The longer alkyl chain has lower mu values, and the stripe periodicity is decisive in reducing energy dissipation during the sliding process. In combination with simulation, the alternate atomic-scale ordered and disordered ionic regions were recognized, whose ratio fundamentally determines the mu values and lubrication mechanism. This finding is an important step toward the practical utilization of ILs with negligible vapor pressure as superlubricating materials in future technological applications operating under extreme conditions.

Automated summary

Ordered monolayer ionic liquid coatings can achieve ultralow friction and exhibit good structure recoverability under high pressure. This extreme lubrication is primarily due to the ordered striped structure driven by the atomic-locking effect between the carbon atoms on the alkyl chain of the ionic liquid and graphite. Controlling the alkyl chain length and stripe periodicity is crucial in reducing energy dissipation.