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.

The achievement of a superlubric state with vanishing friction and negligible wear has important applications in minimizing energy dissipation and prolonging the service life of moving mechanical systems. However, the search for a superlubricious oil system applicable to industrial fields remains a major challenge. In this work, we demonstrate for the first time that precisely employing polyether modification for silicone oil molecules could induce direct superlubricity and superlow wear for engineering steel tribopairs. Superlubricity originates from the fact that polyether-modified silicone oil (PESO) can effectively employ polyether functional groups to interact with friction surfaces, during which a complex tribochemical reaction process can be induced under the catalytic role of friction, where an organic lubricious film composed mainly of carbon, silicon and oxygen can be induced in situ, which can not only effectively passivate friction surfaces but also enable superlubric sliding by virtue of its easy-to-shear nature. Furthermore, iron oxides and chromium oxides could also be confirmed to be distributed within the tribofilm, which is desirable for increasing the load-bearing capability of the tribofilm and toughness. Thus, a remarkable superlubricity of 0.01 without running-in combined with superlow wear was realized at the same time. The results of this work show high promise in promoting the industrial use of oil superlubricity and revolutionizing the development of mechanical systems.

Friction remains as the primary mode of energy dissipation and components wear, and achieving superlubricity shows high promise in energy conservation and lifetime wear protection. The results in this work demonstrate that direct superlubricity combined with superlow wear can be realized for steel/Si₃N₄ contacts on engineering scale when polyhydroxy alcohol solution was selectively modified by amino group. Macroscopic direct superlubricity occurs because 3-amino-1,2-propanediol molecules at the friction interface could be induced to rotate and adsorb vertically on the friction surface, forming in-situ thick and dense molecular films to passivate the asperity contacts. Furthermore, amino modification is also conducive to improving the lubrication state from boundary to mixed lubrication regime by strengthening the intermolecular hydrogen bonding interaction, presenting enhanced load-bearing capability and reduced direct solid asperity contacts. Thus, direct superlow average friction of 0.01 combined with superlow wear are achieved simultaneously. The design principle of direct superlubricity and superlow wear in this work indeed offers an effective strategy to fundamentally improve energy efficiency and provide lifetime wear protection for moving mechanical assemblies.