Synthesis of polyzwitterionic carbon dots with superior friction and fatigue control behaviors under water lubrication

Water lubrication is indispensable for industrial domains, meaning that the tribological behaviors of water are essential for practical applications and should be improved. Herein, a class of zwitterionic polyethyleneimine-grafted carbon dots (CDs-ZPEI0.6-10k) were rationally conceived and synthesized by the facile ring-opening reaction between 1,3-propanesultone (PS) and the PEI0.6-10k skeletons onto CDs-PEI0.6-10k. The intrinsic hydration effect of zwitterionic groups endowed the CDs-ZPEI0.6-10k with superior dispersibility and lubricity in water. The tribological results confirmed that the CDs-ZPEI10k with copious hydration and adsorption sites not only maximally reduced the wear rate and friction coefficient for water by 66.1 % and 72.5 % but also performed steadily under harsh conditions, which benefited from the strong hydration lubrication and ball-bearing function of CDs-ZPEI10k. The worn surface analyses evidenced that the CDs-ZPEI10k could be compacted into a uniform tribofilm with a thickness of about 320 nm to reduce friction while restraining the fatigue damage on the rubbing steel surfaces. Undoubtedly, the hydration, adsorption, and deposition synergistically induce the excellent tribological performances of CDs-ZPEI10k. This study proposed a feasible strategy for designing and synthesizing polyzwitterionic CDs, enabling a high-efficiency aqueous lubrication system with robust friction and fatigue control behaviors.