Robust pH-responsive double-layered self-healing coating with synergistic effects of tannic acid and Ce ions applied on Mg alloy via the phytic acid pretreatment

Synergistic effect of various inhibitors can impart excellent self-healing properties to organic coatings. Here, we designed a pH-responsive double-layered self-healing system (PCe/DMS-TA@CS-EP) comprising the underlying phytic acid conversion film containing Ce ions and the upper epoxy coating (EP) involving tannic acid (TA)-loaded dendritic mesoporous silica (DMS) encapsulated with chitosan (DMS-TA@CS). The phytic acid conversion film, as a pretreatment layer, can make the adhesion force of PCe/DMS-TA@CS-EP/substrate (8.32 MPa) increase by approximately twofold compared with EP/substrate (4.02 MPa). Meanwhile, its micro-cracks are also employed to load Ce ions. DMS-TA can be wrapped by CS through electrostatic interactions. TA is released from DMS-TA@CS in response to pH stimulation. The superior self-healing abilities of PCe/DMS-TA@CS-EP mainly originate from the synergistic effect of TA and Ce ions. The low frequency impedance modulus of PCe/DMS-TA@CS-EP (9.94 × 10¹⁰ Ω·cm²) is two orders of magnitude higher than that of EP (8.45 × 10⁸ Ω·cm²) after 60 days of immersion, indicating that PCe/DMS-TA@CS-EP possesses durable anti-corrosion performance. This synergistic strategy will offer a highly effective approach for preventing/mitigating the corrosion of metal.