Improving the self-healing performance of the water-borne epoxy anticorrosion coating in 3.5 wt% NaCl solution using acid and alkaline dual sensitive organic microspheres

Acid-alkaline double sensitive Eudragit microspheres embedded with corrosion inhibitor 8-hydroxyquinoline (8HQ@Eu) were prepared by a low-cost one-step method, and a novel coating was designed to improve the self-healing performance of the water-borne epoxy resin in 3.5 wt% NaCl solution by using the 8HQ@Eu as smart anti-corrosive carrier. The results of electrochemical impedance spectroscopy (EIS) showed the low-frequency impedance modulus (|Z|0.01Hz) of the scratched coating was about 10 times higher than that of the pure epoxy coating in the presence of 8HQ@Eu microspheres after 30 d of immersion, and the oxide film resistance and charge transfer resistance of the 8HQ@Eu sample increased about 10 times and 8 times respectively due to the covering of corrosion inhibitor protective film. While the results of scanning vibrating electrode technique (SVET) indicated the corrosion current of the 8HQ@Eu sample in the scratched area decreased to more than an order of magnitude lower than that of pure epoxy coating within 24 h. Salt spray test indicated that the substrate corrosion and coating delamination near the scratched area were significantly inhibited. XPS analysis directly confirmed that the corrosion inhibitor was delivered to the corroded sites.