A Mussel-Inspired Polymer-Network Tribofilms Deliver Oil-Based Macroscale Superlubricity on Engineering Steel

Superlubricity (friction coefficient (COF) ≤ 0.01) offers a promising solution to mitigate the global challenges of friction-induced energy consumption and material wear. Despite recent advances, developing oil-based (non-aqueous) superlubricity systems remain highly challenging, particularly on metallic surfaces. Herein, inspired by mussel adhesive chemistry, we report a novel strategy utilizing the molecular self-assembly concept to actively construct a tribofilm with ultralow shear resistance, enabling robust oil-based superlubricity. By incorporating dopamine (DA) as a functional block into an ethylene glycol (EG) lubricant, this system demonstrates an ultralow COF (< 0.01) and an extremely low wear rate (1.9 × 10^-17 m³N^-1m^-1) on the boronized steel throughout a 6-h (216 000 cycles) durability test. From an atomic perspective, DA molecules play a dual role at the sliding interface: i) undergoing self-polymerization and capturing EG molecules to form a network-like carbonaceous tribolayer, and ii) forming strong chemical bonds with the substrate to securely anchor the tribolayer. This tribolayer exhibits low interfacial adhesion, only 20% of that observed with pure EG lubrication, significantly reducing shear strength and energy dissipation, ultimately facilitating superlubricity. This study translates the molecular self-assembly concept into a broadly applicable tribological solution, opening new avenues for developing next-generation, high-performance superlubricity materials.