Synthesis of Eco-Friendly Carbon Dots as Self-Repairing Additives of Polyalphaolefin by Means of a Green Solvation Effect

Ionic Nitrogen-Doped Carbon Dots as Nonpolar Lubricant Additives at Low Effective Addition

The poor compatibility with nonpolar lubricant still hinders the application of carbon dots (CDs) in lubrication. In addition, research proves that the existence of ionic structure and active groups on CDs are conducive to their lubricity. In order to obtain the ionic structures and good oil compatibility synchronously, a kind of ionic nitrogen-doped CDs (NCDs) was synthesized via the alkylation of nitrogen in NCDs and anion exchange. The new material could exhibit good tribological performance as poly alpha olefins (PAO4) additives with low addition. Moreover, an ionic liquid, [N44HH][DEHP], with the same anion was chosen as a comparison to investigate the role of NCD cations. The surface analyses demonstrate that NCD cations and phosphate ester anions adsorb on the friction interface to play a synergistic lubrication role during the friction process, which could generate a superior carbon-based tribofilm.

Synthesizing Benzotriazole Group-Terminated Carbon Dots as Multifunctional Additives of Poly(ethylene glycol)

Long running-in period and corrosion problems have greatly hindered the practical applications of poly(ethylene glycol) (PEG) lubricants. In this work, benzotriazole group-terminated carbon dots (BT-CDs) were specifically synthesized through a facile solvothermal method. The benzotriazole groups on BT-CD surfaces not only imparted them excellent dispersibility in the PEG base oil but also brought in outstanding anticorrosion ability for BT-CDs. With the aid of the coordination effects between benzotriazole groups and metal atoms, the BT-CDs could quickly and solidly adsorb onto the steel surface to form a dense adsorption layer, which resulted in an amazing phenomenon, i.e., the disappearance of the running-in period for the friction test. Adding 5.0 wt % BT-CDs reduced the friction and wear of PEG200 by 49.16 and 49.52%, respectively. When the duration was prolonged from 20 to 120 min, these values were further enlarged to 53.77 and 60.71%. The worn surface characterization demonstrated that the BT-CDs induced the generation of robust lubricating films on the frictional interfaces, accounting for their distinguished tribological performance. Considering the superior anticorrosion ability and the potential possibility of avoiding the running-in period, the BT-CDs are expected to be developed as particularly promising additives toward PEG.

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-g-PEPMA) have been controllably synthesized and used as multifunctional lubricant additives of poly(ethylene glycol) (PEG200). The polymers on the surfaces of CD-g-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-g-PEPMA as an additive showed outstanding rust resistance and tribological performance. Among CD-g-PEPMA-X (X represents the polymerization time), CD-g-PEPMA-2 (X = 2 h) exhibited the best tribological performance. At the optimum c of 2.0 wt %, CD-g-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-g-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 Fe2(CO3)3, Fe3C, and FePO4 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.