Waterborne epoxy coating with excellent barrier and self-healing properties for long-term corrosion protection

Herein, an intelligent anticorrosive coating with superior barrier and self-healing properties was prepared. Molybdate (MoO42-) intercalated layered double hydroxide (MIH) was synthesised and polydopamine (PDA) shell was grown on MIH surface to prepare MIH@PDA (PMIH) material. PMIH was assembled on graphene (Gr) sheet through pi-pi interaction to obtain the Gr@PMIH composite. The anticorrosive coating was prepared by incorporating Gr@PMIH into the epoxy resin. The PMIH material demonstrated a stimulus-response capacity due to the solubility of polydopamine in acidic conditions. In addition, the ion-exchange properties of the layered double hydroxide (LDH) facilitated the release of the encapsulated molybdate corrosion inhibitor between LDH layers and the adsorption of chloride ions. This mechanism was corroborated by ultraviolet-visible (UV-vis) spectroscopy results. Electrochemical impedance spectroscopy (EIS) results revealed that the incorporation of MIH and Gr@PMIH materials considerably enhanced the low-frequency (0.01 Hz) impedance modulus. Among the tested ratios, Gr@PMIH/waterborne epoxy coatings (WECs) (3:7) exhibited the most effectively long-term corrosion protection. EIS measurements of the scratched coatings confirm the superior corrosion resistance and inhibition properties of Gr@PMIH/WECs (3:7). Furthermore, after 400 h of salt spray testing, substrates coated with Gr@PMIH/WECs (3:7) showed the least amount of corrosion products and blisters around surface scratches, affirming its exceptional long-term corrosion protection performance. Thus, the excellent barrier and stimuli-responsive characteristics of the Gr@PMIH material endowed the coating with enhanced long-term corrosion resistance and intelligent protection capabilities.