Polyelectrolyte-grafted carbon nanotubes: Synthesis, reversible phase-transition behavior, and tribological properties as lubricant additives

A novel polyelectrolyte-grafted multiwalled carbon nanotubes (MWCNTs-g-PILs) which possesses a hard backbone of MWCNTs and a soft shell of brush-like poly (ionic liquids) (PILs) has been synthesized via the surface atom transfer radical polymerization (ATRP). Chemical structure and the grafted PILs quantities of MWCNTs-g-PILs were determined by FTIR, TGA, and XPS. TEM and FE-SEM observations indicate that the nanotubes were coated with a PILs layer, exhibiting core-shell nanostructures with the PILs chains as the brush-like or hairy shell and the MWCNTs as the hard backbone. Furthermore, the effect of counter-anions on the solubility of MWCNTs-g-PILs was investigated. The results indicate that relative solubility of MWCNTs-g-PILs in various solvents could be switched by anion exchange. This tunable solubility results in the formation of the cycle of reversible phase-transition. Tribological property of MWCNTs-g-PILs as additives in base lubricant 1-methyl-3-butylimidaaolium hexafluorophosphate (LP104) was evaluated using an Optimol SRV oscillating friction and wear tester, confirming that MWCNTs-g-PILs are the excellent antiwear and friction-reducing additives, which can amend the tribological properties of base lubricant significantly. This is attributed to the good dispersibility and core-shell structure of MWCNTs-g-PILs. These results reported in this work may open primarily toward constructing a bridge among carbon nanotues (CNTs), ILs, and lubricant additives and secondarily to prove that CNTs (modified CNTs) as lubricant additives are promising candidates.