Tribological behaviors of polyelectrolyte capped carbon nanoparticles in polyethylene glycol
Zhu Liang, Baogang Wang, Mina Luo
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.