Preemptive Thermochromic Smart Coating for Visual Friction Damage Recognition and Corrosion Protection in Offshore Structures.

Steel cables serving in offshore energy systems are prone to rapid degradation under the coupled effects of friction-induced wear and marine corrosion, leading to severe safety and reliability concerns. Early recognition of micro-defect initiation and real-time damage monitoring remain formidable challenges due to the difficulty in detecting sub-surface micro-damage. Herein, we present a sandwich-structured thermochromic smart coating that enables preemptive, visual detection of frictional heating prior to irreversible damage. The coating integrates silica-encapsulated thermochromic microcapsules (TC@SiO₂) comprising crystal violet lactone (CVL), bisphenol A (BPA), and n-hexadecanol as a responsive sensing layer between polyurea (top) and epoxy (bottom) matrices. Upon frictional heating, electron transfer between CVL and BPA induces C─O─C bond cleavage and chromophore disruption, triggering a solid-liquid phase transition and color fading that visually warning micro-damage events. Meanwhile, hydrogen-bond interactions between the microcapsules and the polymer network further enhance mechanical robustness and coating integrity, yielding superior tribological performance (5.86 × 10⁻⁵ mm³ N⁻¹ m⁻¹) and long-term corrosion resistance (5.144 × 10⁹ Ω·cm² after 70 days immersion). This work establishes a cost-effective and intuitive strategy for early friction monitoring, offering a new paradigm for intelligent protection of marine structural materials.