Tribological behaviors of polyelectrolyte capped carbon nanoparticles in polyethylene glycol

Abstract

Polyethyleneimine (PEI) capped carbon nanoparticles (CNPs-PEI), gained by hydrothermal treatment of citric acid and PEI, were transformed into the polyelectrolyte capped CNPs (CNPs-PEI-NTf₂) by HCl protonation process and anion exchange process between Cl⁻ and bistrifluoromethanesulfonimide (NTf₂⁻). The CNPs-PEI-NTf₂ exhibited superb comparability with polyethylene glycol (PEG200). Their tribological behaviors as the lubricant additives of PEG200 were evaluated under the four-ball mode and steel/steel contact. Amazingly, adding particularly low amount (0.05 wt%) of CNPs-PEI-NTf₂ made the friction coefficient and wear volume of PEG200 reduce by 66.1% and 86.6%, respectively. The surface analysis results of wear scars demonstrated that the CNPs-PEI-NTf₂ as additives not only directly participated in the formation of mixed boundary lubrication films through the synergistic lubrication effect between the PEI-NTf₂ groups and CNPs of CNPs-PEI-NTf₂, but also should play the rolling, mending and polishing effects on the rubbing surfaces, and hence exhibited the outstanding friction-reducing and anti-wear functions.

Keywords:

• Carbon nanoparticle
• polyelectrolyte
• polyethylene glycol
• friction
• wear
• lubricant additive

Additional information

Funding

This work was supported by National Natural Science Foundation of China (No. 51975493) and the Postdoctoral Science Foundation Funded Project of China (2015M582567).