Achieving one-step macroscale superlubricity through robust PVDF/PMMA composite coatings

Macro-superlubricity is crucial for reducing energy dissipation during friction processes and extending the service life of high-end engineering equipment. Fluoropolymers, with their extremely low surface energy, are ideal anti-friction materials. However, they still exhibit certain limitations in achieving stable superlubricity and superior mechanical properties. Here, we report a high-performance PVDF/PMMA composite coating constructed via a polymer blending strategy. Under glycerol lubrication conditions, the composite coatings (PVDF/PMMA ratios of 8:2 and 6:4) demonstrated outstanding tribological properties, with friction coefficients as low as 0.008 and 0.006, respectively. Notably, this composite coating can achieve “one-step superlubrication” at the moment of startup. This behavior is mainly attributed to the synergistic effect between the coating’s surface microtopography and mechanical strength. At the 8:2 ratio, the coating not only exhibits a relatively smooth and flat surface but also achieves a balance between stiffness and toughness (tensile strength: 13.91 MPa; elongation at break: 13.3%). As a result, it effectively preventing brittle fracture during sliding. Furthermore, molecular dynamics simulations revealed the atomic-scale lubrication mechanism, showing that glycerol preferentially adsorbs on the Si₃N₄ ball rather than the coating surface during friction, thereby inducing boundary slip behavior. This work provides novel insights for designing polymer-based superlubricant systems with superior tribological and mechanical properties, expanding their applications in advanced engineering fields.