Tailoring the tribological performance of poly(ionic liquid)s brushes capped carbon dots by transforming the anion species

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.

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

The eco-friendly menthol-modified carbon dots (CDs-Menth) were synthesized for the first time and exhibited the particularly promising application potential as additives of polyalphaolefin (PAO4). On the one hand, the CDs-Menth could be well dispersed into PAO4 with excellent and long-term dispersion stability via a convenient and green mean, that is, the solvation effect of petroleum ether. This mean was far more advanced to current strategies such as chemical modifications and adding dispersants. On the other hand, the CDs-Menth as additives possessed not only the duty-bound merits such as the distinguished friction-reducing, anti-wear, and load-carrying functions, but also an amazing ability of self-repairing effect. The repairing rate of lower disc in the ball-on-disc friction pair lubricated with CDs-Menth/PAO4 lubricant (2.5 wt %) was about 19.3% if the friction duration was prolonged from 20 to 120 min. Meanwhile, the wear volume reduction for PAO4 caused by CDs-Menth remarkably increased from 43.5 to 74.6%. By virtue of the self-repairing effect, the CDs-Menth could form the tough and tensile boundary lubrication films on the rubbing surfaces, not only tremendously reducing the friction and wear of friction pair, but also hopefully protecting the friction interfaces from the potential oxidation and corrosion.

Influence of Structural Disorders on the Tribological Behavior of Phosphate-Intercalated Layered Double Hydroxide Additives in Polyalphaolefin

In this work, several phosphate-intercalated Mg-Al layered double hydroxides (LDHs) were synthesized and evaluated as solid lubricant additives in polyalphaolefin (PAO-4) by means of tribotesting on coupled GCr15/cast iron contacts. The effects of test parameters such as normal loads, additive concentrations, and substrate surface roughness were investigated, while the LDH crystal structure received considerable attention. Several types of structural disorder after anion exchange were identified based on X-ray diffraction (XRD) analysis. The unstable structures promote feasible shearing during sliding to improve friction and wear. In addition, antiwear properties correlate well with the anion charge number or the quantity of anion in the interlayer region. Overall, the tribological performance increased in the order HPO₄^2--LDH < PO₄^3--LDH < P₂O₇^4--LDH < (PO₃)₆^6--LDH. (PO₃)₆^6--LDH demonstrated the best antiwear performance with a reduction of 69% of the ball volume loss compared to PAO-4 oil due to the synergy of the disordered stacking LDH sheets and flexible ring structure of the (PO₃)₆^6- anion. Furthermore, on polished surfaces, the coefficient of friction (COF) of the (PO₃)₆^6--LDH sample dropped significantly by 26%, while the wear loss reduction of more than 80% was also substantial compared to the base oil sample. A performance comparison between the best-performing LDH additive was also conducted against popular nanomaterials, such as hexagonal boron nitride (BN), graphene nanoplatelets (GNPs), and titanium oxide (TiO₂). The performance of (PO₃)₆^6--LDH was close to that of GNPs.