Bio-inspired hydration lubrication enabled by crosslinked polyacrylamide particles in epoxy composite coatings

Developing epoxy coatings capable of stable lubrication in aqueous environments remains challenging due to the low viscosity and poor retention of water at sliding interfaces. In this study, a bio-inspired epoxy/polyacrylamide (EP/PAM) composite coating was constructed to achieve hydration-regulated lubrication and water-triggered functional response. Crosslinked polyacrylamide particles were embedded into the epoxy matrix as dispersed water-storage units, enabling constrained swelling and surface reconstruction upon water exposure, thereby regulating the interfacial hydration state and real contact behavior. By tailoring particle content and crosslink density, the lubrication performance could be rationally controlled. The optimized EP/PAM1–25 coating exhibited a minimum coefficient of friction of 0.10 and a specific wear rate of 0.91 *10⁻ 4 mm 3 ·N⁻ 1 ·m −1 , corresponding to reductions of approximately 60% and 80%, respectively, compared with pure epoxy. The tribological performance showed a non-monotonic dependence on crosslink density, reflecting the balance between swelling capacity and interfacial lubrication stability. The coating maintained low friction under varying loads and sliding speeds. Device-level demonstrations further confirmed pressure-driven drainage and leakage-triggered alarm activation enabled by water-induced friction transition. This work provides a controllable strategy for designing adaptive hydration-lubricated coatings and broadens their potential in water-responsive systems.