Core–Shell Cu@PDA Nanoparticles: Synergistic Adhesion and Active Repair for High-Performance Water-Based Lubrication

Copper nanoparticles are widely used for surface repair due to their inherent softness. However, traditional Cu nanoparticles (NPs) rely on passive mechanical interlocking, which has low repair efficiency, poor stability, and reduces tribological efficiency. To address these issues, this study proposes a chemically active repair strategy based on polydopamine (PDA)-coated copper nanoparticles with a core-shell structure (Cu@PDA). The Cu@PDA nanoparticles significantly improved the hydrophilicity of the friction interface, reducing the water contact angle from 64° to 42°, thereby facilitating the stable formation of lubricating films. Under loads ranging from 49 to 147 N, the Cu@PDA suspensions exhibited excellent tribological performance in a copper-copper friction pair, achieving up to a 41.2% reduction in the friction coefficient and a 78.3% reduction in the wear rate. Microscopic morphology and wear scar analyses revealed that the enhanced lubrication performance resulted from two synergistic mechanisms: (1) under friction, Cu@PDA nanoparticles demonstrate strong underwater adhesion and spontaneously form a stable directional transfer film for active wear repair and (2) nanoparticles fill wear furrows, enhancing surface topography and lubricating film continuity. This study addresses unstable adhesion and delayed repair in water-based lubricating films, offering a novel strategy for durable aqueous lubrication systems with potential in high-load applications like marine propulsion and hydraulic systems.