Synthesis of Poly(ionic liquid)s-Functionalized Carbon Dots with Superior Tribological Stability and Potential-Controlled Friction Effect under Oil Lubrication

Potential-controlled friction provides the possibility for the active and dynamic regulation of the tribological behaviors of nanoadditives. However, the major challenge in achieving this goal is how to ensure the outstanding dispersibility and conductivity of nanoadditives in lubricants. Herein, the poly(ionic liquid)-functionalized carbon dots (CDs-PILs) with good dispersion stability in PEG200 were designed and synthesized from the polyethylenimine-grafted CDs (CDs-PEI). Compared with PEG200, the CDs-PILs (5.0 wt %)/PEG200 dispersion not only realized 38.2% and 52.3% reductions in friction and wear, respectively, but also showed superior tribological stability in heavy load (∼2.93 GPa), high frequency (10 Hz), long duration (300 min), and various start-stop modes due to the robust adsorption and nanolubrication effects of CDs-PILs at friction surfaces. Noticeably, the lubricity of dispersion with higher ionic conductivity (158.2 μS/cm) than PEG200 (5.7 μS/cm) presented an obvious response to the voltage range of -10 to +18 V, supporting the eminent potential-controlled friction characteristics of CDs-PILs. In addition, the deposition of uniform tribofilm with about 76 nm thickness was observed on the rubbed surfaces, which contributed to the ideal tribological properties of the CDs-PILs. This study proposed a simple approach for the CDs-PILs synthesis, enabling the high-efficiency potential-controlled friction of nanoadditives under oil lubrication.