Ionic liquid capped carbon dots as a high-performance friction-reducing and antiwear additive for poly(ethylene glycol)†
Abstract
Ionic liquid (1-aminopropyl-3-methyl-imidazolium bromide) capped carbon dots (CDs-Br), with a mean particle size of 1.73 nm and poor crystallinity, have been successfully synthesized by a one-pot pyrolysis method. The CDs-NTf2 were obtained from the CDs-Br by an anion exchange reaction between Br− and N(CF3SO2)2− (NTf2−). The NTf2− endowed the CDs-NTf2 with wonderful dispersion stability in poly(ethylene glycol) (PEG). The tribological performances of CDs-NTf2 as the lubricant additive for PEG were investigated in detail using a four-ball model by altering the concentration of CDs-NTf2, the test load and the duration. The results demonstrated that these CD-NTf2-based additives exhibited excellent friction-reducing and antiwear properties. In particular, the friction coefficient and wear scar diameter (WSD) of lower balls lubricated by PEG under 392 N correspondingly reduced by 70% and 33% when 0.3 wt% of CDs-NTf2 was introduced. The WSD reduction further increased by 45% when the test load was increased to 600 N. Moreover, the CD-NTf2-based additives could work for a long time without weakening the lubrication capabilities. The lubricating mechanism of CD-NTf2-based additives has also been proposed and illustrated that the synergistic lubricating effect of CDs-NTf2, including film lubrication of IL groups and nano-lubrication of carbon cores such as rolling, mending and polishing effects, might account for their outstanding tribological behaviors. The above results indicate that CDs are expected to be utilized as a kind of designable and high-performance lubricant additive and find wide applications in machinery and equipment.
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