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

Abstract

The tribological performance of poly(ionic liquid)s brushes capped carbon dots (CDs-PILs-X) as the additives of polyethylene glycol (PEG200) were well tailored by transforming the anion species (X-), where the X- were hexafluorophosphate (PF6-), bis(trifluorosulfonyl) imide (NTf2-), bis(salicylato) borate (BScB-) and oleate (OL-), respectively. Despite all of the CDs-PILs-X as additives of PEG200 exhibited excellent friction reduction and wear resistance properties, their tribological performance followed the order of CDs-PILs-OL > CDs-PILs-BScB > CDs-PILs-NTf2 > CDs-PILs-PF6. Typically, at a concentration of 2 wt%, the CDs-PILs-OL, CDs-PILs-BScB, CDs-PILs-NTf2 and CDs-PILs-PF6 made the average friction coefficient and wear volume of PEG200 reduce by 58.6 and 85.4%, 45.5 and 76.3%, 33.3 and 75.7%, and 28.6 and 72.6%, respectively, confirming the distinct influences of anion species on the tribological performance of CDs-PILs-X. The CDs-PILs-OL exhibited the best friction reduction and wear resistance performance because the anions of OL- with the lowest steric hindrance could form the densest absorbing layers and hence the most compact boundary lubrication films on the rubbing surfaces. The anions of PF6- and NTf2- might decompose to release corrosive substances (such as HF) during the friction process, largely weakening the lubrication functions of CDs-PILs-NTf2 and CDs-PILs-PF6. The CDs-PILs-OL can be a kind of promising lubricant additives for PEG200 because of their impressive performance, long service life, low cost and environmental friendliness.