Polydopamine-stabilized ZIF-8: Improved water stability and lubrication performance

[Display omitted] •Improved water stability of ZIF-8 is attributed to hydration of the PDA surface.•The water stability of ZIF-8 is the guarantee for good lubrication performance.•ZIF-8@PDA additives have good dispersion stability and solvent resistance.•ZIF-8@PDA enters the friction gap and generates a double layer of protective film. ZIF-8, a novel lubricant additive, is considered to have great potential in reducing friction and wear due to large specific surface area, thermal stability and mechanical flexibility. However, ZIF-8 nanoparticles readily hydrolyze in aqueous solutions, transforming into large-sized lamellar and rod-like materials, which is a major bottleneck as a water-based lubricant additive. Herein, a strategy is proposed to functionalize ZIF-8 via mussel-inspired polydopamine (PDA) polymerization process to improve its lubrication stability in the water phase. The modified ZIF-8 (PDA@ZIF-8) can firmly “locked” water molecules on the surface of PDA to protect internal structure of ZIF-8, and improve its dispersion and stability of ZIF-8 in water. Moreover, ZIF-8@PDA tribofilm and iron oxide chemical protection film are formed during the friction process, and the low shear strength water layer between the contact surfaces contribute to achieving powerful synergistic lubricating effects, resulting in friction coefficient and wear track width reduce by 65% and 66%, respectively. Therefore, this work provides a promising alternative for expanding the practical application of ZIF-8 in aqueous environment and tribology.