Architecting cobblestone-like microstructures in PAI coatings: A dual-functional filler and lubricant polarity strategy for extreme wear resistance

The intrinsic compromise between high load-bearing capacity and low friction in polyamide-imide (PAI) coatings severely limits their performance in extreme hydraulic environments. Here, we demonstrate a materials design paradigm that overcomes this trade-off by synergizing interface-engineered ZnO nanoparticles with lubricant polarity control. Dioctyl phosphate (P204) functionalization creates dual-action ZnO@P204 nanoparticles, which enhance interfacial bonding by 38% and provide exceptional dispersion stability. At an optimal 1.0 wt.% loading, these particles template a cohesive, cobblestone-like microstructure that endows the coating with a load-bearing capacity >100 MPa. When coupled with the polar lubricant PEG400, a triple-action tribological mechanism is unlocked, integrating microstructural reinforcement, shear-induced boundary film alignment, and chemically tailored interfacial slip, thereby achieving ultralow friction (μ=0.011) and wear (2.6×10⁻⁷ mm³/(N·m))—a fivefold enhancement over state-of-the-art PAI composites. The fundamental principle of nanoparticle-lubricant cooperativity established herein offers a universal design framework for next-generation intelligent wear-resistant coatings.