Outstanding lubrication properties of carbon dot-based ionic liquids

Although carbon dots (CDs) have attracted much attention due to their excellent lubricity and high load-carrying capacity as lubricant additives, the deficiency of easy agglomeration and the feature of solid state still restrict the application of CDs in the field of lubrication engineering. In order to break through the above limitations, novel liquid CD materials, carbon dot-based ionic liquids (CDILs), were synthesized via ionic modification of CDs with organic ammonium cations endowing new functions as novel liquid lubricants, which demonstrates that CDILs provide better lubrication performance than classical ILs ([BMIM][BF4]) and at room and high temperature (30 °C and 100 °C). More importantly, the newly synthesized [N888H][CDs] containing tertiary ammonium cations with long alkyl chains exhibits the best lubrication performance. The resultant analyses give direct evidence that CD anions play a surprising role in improving the lubricity and protecting the steel/steel friction pairs, growing robust tribofilm with abundant CDs on the worn surfaces. Hence, it can not only offer fundamental insights into the formation of the tribofilm, but also provide a method for modifying CDs to promote their lubricity as liquid lubricants.