Redox-triggered controlled release systems-based bi-layered nanocomposite coating with synergistic self-healing property

Redox-triggered smart nanocontainers, RTSNs 1, assembled by installing supramolecular switches onto the exterior surface of mesoporous silica nanoparticles, were successfully synthesized. The reversible transition upon redox stimuli from self-complexation to self-dissociation of supramolecular switches, which are in the form of beta-cyclodextrin monofunctionalized with a ferrocene moiety, realizes switch behavior and regulates the release of p-coumaric acid (CA) encapsulated in mesoporous silica nanoparticles. Based on these facts, a bi-layered nanocomposite coating was designed and coated on the surface of AA2024 by successive deposition of a Ce(IV)-doped ZrO2-SiO2 sol-gel coating and an RTSNs 1 incorporated ZrO2-SiO2 coating. The bi-layered nanocomposite coating shows high barrier performance, effectively delaying the corrosion process occurring on the metallic surface in 0.5 M NaCl solution for 20 days. Once the bi-layered nanocomposite coating suffers local damage, Ce(IV) salt meets with RTSNs 1 in the scratched area and thus open the supramolecular switches, resulting in the release of the organic corrosion inhibitors, CA molecules. In the meantime, Ce(IV) salt is reduced to the inorganic corrosion inhibitor, Ce(III) salt. The combination of CA and Ce(III) produces a synergistic inhibition effect, which rapidly repairs the damaged surface and provides durable self-healing functionality.