A double-layered self-healing coating system based on the synergistic strategy of cysteine and iron polyacrylate for corrosion protection

Nanocontainers loaded with corrosion inhibitors are usually added to organic coatings to achieve self-healing of the coating. However, the amount of nanocontainers that the coating can accommodate is limited. Excessive addition of nanocontainers will damage the integrity of the coating, while too little addition will lead to its insufficient self-healing ability. Here, we prepared a double-layered self-healing coating system (C-DMS-EP/P-DMS-EP) consisting of a bottom epoxy coating containing cysteine (CysH) loaded dendritic mesoporous silica (DMS) (C-DMS-EP) and an upper epoxy coating containing iron polyacrylate (PAAFe) loaded DMS (P-DMS-EP) based on the synergistic effect of CysH and PAAFe. It can achieve more efficient self-healing ability for Q235 steel. The experimental results exhibit that PAAFe can not only accelerate the oxidation of CysH but also capture the hydrogen ions generated during the oxidation process, thereby exhibiting excellent corrosion resistance. Electrochemical impedance spectroscopy (EIS) results show that the low frequency impedance modulus (|Z|0.01 Hz) of C-DMS-EP/P-DMS-EP is nearly-two orders of magnitude higher than that of pure epoxy coating (EP) after 40 days of immersion in 3.5 wt% NaCl solution. Moreover, the self-healing efficiency (eta(s)) of C-DMS-EP/P-DMS-EP with an artificial scratch (C-DMS-EP/P-DMS-EP@AS) gradually changes from negative to positive as the immersion time increases. The preparation method for this double-layered self-healing coating system proposed in this work will provide a new idea for constructing high-performance self-healing coatings.