A Multifunctional Smart Coating with Damage Visual Warning, Self-Healing, Antibacterial, and Long-Term Anti-Corrosion Properties for Marine Applications

In harsh marine environments, polymer coatings are prone to undetectable microdamage, increasing maintenance costs and safety risks. To achieve visual monitoring and precise self-repair of microdefects, this study constructed a smart protective coating integrating damage warning, self-healing, antibacterial properties, and long-term corrosion protection. The coating was fabricated by embedding mesoporous polydopamine nanospheres loaded with Rhodamine B (RhB) into a thermally responsive epoxy resin matrix. The innovation lies in the synergy between the fluorescent nanofillers and the thermally responsive matrix. Based on this synergy, the coating exhibits multiple smart functions: (1) precise localization of microdefects via significant fluorescence enhancement at damaged sites; (2) a graded warning mechanism from coating damage to metal corrosion, triggered by specific binding of RhB with Fe3+ and subsequent fluorescence quenching. Under 808 nm near-infrared (NIR) light irradiation, the coating rapidly heats to 85.5 °C (approximately 4 times that of the neat epoxy coating), further triggering two additional key functions: (3) activation of the shape-memory effect to close microcracks, with impedance recovering by more than 2 orders of magnitude compared to the scratched state; (4) high antibacterial performance, with bactericidal rates of 99.8% against Staphylococcus aureus (S. aureus) and 96.69% against Escherichia coli (E. coli). Electrochemical impedance spectroscopy (EIS) confirmed superior barrier performance: after 90 d of immersion, the impedance modulus remained at 1.31 × 109 Ω·cm2, approximately 1 order of magnitude higher than that of the neat epoxy coating. In summary, this study provides an effective strategy for monitoring anticorrosion coating failure and triggering repair, offering a reliable design approach for next-generation intelligent protective materials for harsh environments such as marine engineering.