N,S-Co-doping enhances tribological properties of solvent-free covalent carbon dot nanofluids

Solvent-free nanofluids have attracted increasing attention in tribological applications due to their distinctive load-bearing lubrication mechanisms, which arise from the synergistic interaction between its surrounding corona/canopy structures. In this study, a nanofluid was developed by incorporating N,S-co-doped carbon dots (N,S-CDs) and Jeffamine M2070 into polyimide (PI) matrix. This composite reduced the COF by 61 % (0.15 ± 0.01) and the wear rate by 95 % (3 ± 0.1643) × 10 −6 mm 3 /N·m compared to pure PI. N,S-CDs adsorbed onto friction surfaces via -NH 2 and -COOH groups, enhancing interfacial bonding and raising peak interface temperature by 126 K. This promoted PI fragment graphitization and robust tribofilms formation. M2070 further smoothed the interface by filling voids. The work proposes a “core-resin interface with casing” strategy for tribological materials in high-load, precision applications.