Superior lubrication effect enabled by soluble carboxylated graphene quantum dots in polyether-modified silicone oil

Achieving robust and reliable ultra- to super-low friction combined with extremely low wear, which is applicable to industrial applications, has always been the pursuit of researchers. In this work, carboxylated graphene quantum dots (CGQDs) were synthesized for dissolution into polyether-modified silicone oil (PESO). The results indicate that CGQDs demonstrate exceptional solubility in PESO, which can be attributed to the favorable charge–transfer interaction between CGQDs and PESO molecules. Tribological tests indicate that the addition of CGQDs to PESO could result in a robust and reliable superior lubrication effect for steel tribopairs under a wide range of testing conditions, with the lowest friction coefficient being approximately 0.02. The investigation of the wear scars indicates that CGQDs can effectively embed into friction contacts due to their ultrasmall size, allowing them to interact effectively with the steel surface through their carboxy groups and therefore forming an in-situ robust CGQDs-based lubricant film. The generated CGQDs-based lubricant film could not only effectively passivate the direct asperity contacts of tribopairs but also provide a shearable path due to its desirable lamellar characteristics. The findings of this work are expected to provide a novel reliable strategy to achieve ultra- to super-lubrication for industrial applications.