Synthesis of Polymer-Grafted Carbon Dots Serving as Multifunctional Lubricant Additives with Excellent Tribological Performance and Additional Rust Resistance Function for Steel/Steel Contact.

Poly(bis(2-ethylhexyl) phosphoric) methacrylic anhydride-grafted carbon dots (CD--PEPMA) have been controllably synthesized and used as multifunctional lubricant additives of poly(ethylene glycol) (PEG200). The polymers on the surfaces of CD--PEPMA not only endow them with particularly excellent dispersion stability but also enhance their adsorbability on the steel surface and embedded stability between the rubbing surfaces. Hence, CD--PEPMA as an additive showed outstanding rust resistance and tribological performance. Among CD--PEPMA-X (X represents the polymerization time), CD--PEPMA-2 (X = 2 h) exhibited the best tribological performance. At the optimum of 2.0 wt %, CD--PEPMA-2 reduced the coefficient of friction and wear volume of PEG200 by 60.1 and 74.0%, respectively. The striking friction-reducing and antiwear functions of CD--PEPMA as additives can be attributed to the synergistic lubrication effect of carbon cores and polymers. The rolling, polishing, and mending effects of carbon cores combined with the favorable adsorbability and reactivity of polymers on steel surfaces synergistically induced the formation of boundary lubrication films on wear track surfaces. The films are composed of tribochemical reaction products such as Fe(CO), FeC, and FePO embedded with carbon cores, tremendously reducing the friction and wear of the friction pair. The research results can provide substantial theoretical guidance and data support for designing and developing high-efficiency polymer-CD integrative multifunctional nanoadditives toward PEG.