In-Situ Generation of Carbon Dots by Mechanochemical Action at the Tribological Interface Leads to Ultralow Friction

Nanomaterials prepared by physical exfoliation or chemical synthesis and used as lubricant additives can enhance the load-bearing capacity of lubricants and reduce the COF. However, the use of shear-induced mechanical strain to trigger molecular fragmentation and rearrangement reactions, thereby directly generating carbon dots (CDs) in situ within the lubricant system, has not yet been reported. A new lubricant, composed of aromatic polyacids, poly(ethylene glycol) (PEG), and water, has been prepared such that it can in situ generate carbon dots through shear friction, thereby achieving the lowest friction coefficient (COF = 0.012) to date in the four-ball model. Under the action of high shear forces at the interface, TA and PEG molecules undergo mechanochemical reactions at the friction interface, in situ generating CDs and consequently resulting in changes in the solution state. The tribofilm composed of CDs, together with the hydrogen-bonding network formed by TA, PEG, and water molecules, provides the lubricating system with the ability to withstand high loads. This finding provides important theoretical and practical guidance for the development of new, highly efficient carbon-dot-based lubricants via an in situ approach.