Double-layered composite coating with enhanced self-healing and anti-corrosion performance based on synergistic effect of l-methionine and vanillin

Nanocontainers loaded with corrosion inhibitors as fillers can endow the organic coating with self-healing abilities. However, the number of nanocontainers that can be added to the coating is limited, and the number of corrosion inhibitors that can be accommodated by the nanocontainers is also limited. These considerably mitigate the anti-corrosion properties of the self-healing coating. Herein, a self-healing double-layered composite coating (MK-VK/EP), l-methionine (L-met)-loaded dendritic silica (KCC-1) nanocontainers modified epoxy coating (EP) as the bottom layer (MK/EP) and vanillin (Van)-loaded KCC-1 modified EP as the top layer (VK/EP), was fabricated on the surface of carbon steel. The results of electrochemical impedance spectroscopy (EIS) show that the low frequency impedance modulus (|Z|0.01Hz) of MK-VK/EP is nearly two orders of magnitude higher than that of MK/EP or VK/EP in 3.5 wt% NaCl solution after 45 days. Furthermore, the self-healing rate (rself-healing) of the scratched MK-VK/EP coating (S-MK-VK/EP) is still much higher than that of the scratched MK/EP or VK/EP in the last two stages of immersion. Meanwhile, there exists no apparent corrosion after 12 h of immersion from the optical image of S-MK-VK/EP. The results show that MK-VK/EP can provide better self-healing corrosion protection performance than the single coating (MK/EP or VK/EP). Hence, the synergistic effect of different corrosion inhibitors can greatly improve anti-corrosion abilities of the coating, which will provide an effective approach for corrosion protection of metal in marine environment.