Study On Ion-responsive Self-healing Epoxy Composite Coating Based On Layered Double Hydroxide

In recent years,with the massive development of marine resources,the issue of marine corrosion has been highly concerned by people.Organic coating is an effective method to deal with metal corrosion,but conventional anti-corrosion coatings are difficult to meet the harsher marine corrosion environment.Functionalized self-healing anti-corrosion coating is an important solution to the marine corrosion environment.At present,it is a hotspot in the research of self-healing coatings to add micro-nano containers loaded with corrosion inhibitors to the coating system,and the stimulus-responsive release of corrosion inhibitors occurs after the coating is damaged,to realize the protection of metal substrates.According to the characteristic of high salt content in the marine environment,layered double hydroxide(LDH)with anion exchange capacity were used as containers loading with organic inhibitors 2-mercaptobenzimidazole(MBI)and 2-mercaptobenzothiazole(MBT),and added into epoxy resin as fillers to prepare ion-responsive self-healing coatings.At the same time,montmorillonite(MMT)with cation exchange capacity was used to load cerium ions and samarium ions as fillers to explore the synergistic effect of corrosion inhibitors on the corrosion resistance of self-healing coatings.First,this paper prepared MBI or MBT intercalated LDH(LDH-MBI and LDH-MBT)by calcination-rehydration method.XRD results showed that the interlayer spacing of the hydrotalcite was significantly increased due to the intercalation of MBI and MBT.FTIR and XPS results also showed that the successful intercalation of MBI and MBT to LDHs.According to the TGA and UV-vis results,it was determined that the loading rate of MBI in LDH-MBI was 29.2%,and that of MBT in LDH-MBT was 29.0%.At the same time,using UV-vis test,it was found that the release of corrosion inhibitors in LDH-MBI and LDH-MBT increased with the increase of Na Cl concentration,and the release of corrosion inhibitors was faster in solutions containing Cl~-,showing a clear ion-responsive ability.In addition,this paper also investigated the corrosion inhibition effect of LDHs on mild steel in different concentrations of Na Cl solution and found that LDHs showed the highest corrosion inhibition efficiency in 7.5 wt.%Na Cl solution.Secondly,LDH-MBI and LDH-MBT were added to epoxy resin in the form of fillers to prepare LDHs/EP coatings.It was found that when the content of LDHs was 3 wt.%,the LDHs/EP coatings had less pores and the best barrier effect on corrosive solution,thus the optimal formulation of LDHs/EP coating was obtained.When the artificially scratched LDHs/EP coating contained 3 wt.%LDHs,this paper used EIS technology to investigate the law of the impedance changing with immersion time in different Na Cl concentration solutions.The above studies showed that the LDHs/EP coating had the highest corrosion resistance when the Na Cl concentration is 7.5 wt.%,and the LDHs/EP coating exhibited a clear ion-responsive ability.Afterwards,the self-healing mechanism of the LDHs/EP coating was proved by LEIS and XPS which the LDHs in the coating could effectively release corrosion inhibitors through ion exchange.Finally,montmorillonites intercalated with cerium ions and samarium ions(MMT-Ce and MMT-Sm)were prepared by cation exchange method.Under the condition of controlling the total content of LDHs and MMTs to 3 wt.%,the effect of the combination of corrosion inhibitors(MBT/Ce and MBI/Sm)on the corrosion resistance of LDHs/MMTs/EP coatings was investigated by changing the ratio of LDHs and MMTs.The EIS results found that when the ratio of LDH-MBT and MMT-Ce is 1:2,the corrosion resistance of LDH-MBT/MMT-Ce/EP coating was significantly better than that of EP coating with LDHs or MMTs alone.At the same time,when the ratio of LDH-MBI and MMT-Sm is 1:1,the corrosion resistance of LDH-MBI/MMT-Sm/EP coating was also significantly better than that of EP coating with LDHs or MMTs alone.The above research on the synergistic effect of corrosion inhibitors in the loaded system provides a new direction for the development of self-healing coatings.