MBT + CVL@Fe3O4 enhanced epoxy coating for self-healing and self-warning performance

Corrosion of carbon steel can result in serious damage, limiting its application in various fields. Considerable protective coatings have been proposed, but they are limited by difficulties in repairing and early warning of coating damage and local metal corrosion. Herein, a dual-functional smart anti-corrosion coating with integrated self-healing and self-warning capabilities was designed and fabricated. Firstly, the MBT + CVL@Fe 3 O 4 composite was prepared by loading corrosion inhibitor 2-mercaptobenzothiazole (MBT) and fluorescent probe crystal violet lactone (CVL) into mesoporous Fe 3 O 4 microspheres. The system demonstrated a stimulus-responsive release of MBT, providing effective corrosion inhibition for Q235 steel. Subsequently, the MBT + CVL@Fe 3 O 4 composite was incorporated as a functional filler into a shape memory epoxy (EP) coating. The results showed that the optimum addition amount of filler was 2 wt% because the MBT + CVL@Fe 3 O 4( 2% ) /EP coating presented the smoother surface, maximum water contact angle, and impedance value under damaged conditions. Based on the photothermal effect of Fe 3 O 4 -based filler combined with the shape memory effect of epoxy resin, when irradiated for 60 s, the surface temperature of the scratched MBT + CVL@Fe 3 O 4( 2% ) /EP was about 55 °C, exceeding its glass transition temperature ( T g  ≈ 49.5 °C). Consequently, the scratch width was markedly reduced, demonstrating effective self-healing of the external coating damage. Moreover, when the coating damage even caused local corrosion of the metal substrate and changes in the pH of the corroded area, the corrosion inhibitor MBT was responsively released, forming a protective film layer to protect the metal substrate from further degradation. The low-frequency impedance |Z| 0.01 Hz values of scratched pure epoxy coating (EP), scratched MBT + CVL@Fe 3 O 4( 2% ) /EP and photothermal healed scratched MBT + CVL@Fe 3 O 4( 2% ) /EP immersed in 3.5 % NaCl solution for 120 h were 4.98 × 10 4  Ω·cm 2 , 4.78 × 10 5  Ω·cm 2 and 1.31 × 10 6  Ω·cm 2 , respectively, which fully illustrated the dual repair function of the coating. Additionally, the CVL loaded in the filler provided the fluorescence color rendering performance of the coating. Under the irradiation of an ultraviolet lamp, the bright blue fluorescence signal can be displayed at the coating damage site, effectively predicting the coating damage. Moreover, CVL can produce fluorescence quenching when localized corrosion occurs on the metal substrate, warning of early corrosion. These results prove the self-warning performance of the anti-corrosive coating.