Macroscopic tribological properties and molecular simulation study of carbon quantum dots modified by ionic liquids

Using amino acid ionic liquids (Ser–TEA) as surface modifiers and citric acid (CA) the carbon source, ionised carbon quantum dots (Ser–CA/CQDs) of uniform size were successfully prepared in this study. They exhibited excellent dispersion stability and tribological performance in an ethylene glycol aqueous solution (EGaq), as revealed using a one-step pyrolysis method. Macroscopic experimental results show that adding 2.0 wt % Ser–CA/CQDs reduces the friction coefficient of EGaq from 0.16 to 0.128, and the wear scar volume decreases by 51.97 %, which is attributed to the formation of a hydration layer and tribofilm. Furthermore, molecular dynamics simulations at the microscopic level revealed that the weak interaction energy between Ser–CA/CQDs and the friction pair surface, combined with the "ball-bearing effect", significantly reduced frictional resistance. Further, the lubrication performance of EGaq improved with the formation of a carbon film and an interface with low shear strength. This process offers a novel atomic-level perspective for understanding and optimising the applications of nanolubricant additives.