Intelligent self-healing anti-corrosive coatings with crosslinked conducting polypyrrole hydrogel network

The cross-linked conducting polypyrrole hydrogel (CPH) network is designed for preparing the corrosion-resistant and self-healing epoxy coatings, which are used for the long-term active corrosion control of Mg alloys substrate in 3.5 wt% NaCl solution. The encapsulated phytic acid (PA) inhibitors are uniformly distributed in the crosslinked CPH network with an encapsulation amount of 16.77%. The inductively coupled plasma–optical emission spectrometry test indicates that the releasing rate of the PA inhibitors from the crosslinked CPH network rises with the increased pH values, reflecting their pH-responsive feature. Afterward, the epoxy coatings impregnated with various contents of the CPH network are coated on the Mg alloy surface, and their corrosion resistance and self-healing performances are evaluated using electrochemical and immersion tests. Results indicate that the epoxy coatings with 5 wt% CPH displays the most durable corrosion-resistant and self-healing performances with the highest coating resistance (4.39 × 10⁵ Ω cm²) and charge-transfer resistance (8.28 × 10⁵ Ω cm²) values even after 28 days of immersion. The encapsulated PA inhibitors continuously release to the cracked region in response to the local pH variations and react with Mg²⁺ ions generated from the active corrosion site. Consequently, an Mg-PA protective layer is formed to suppress further corrosion activities. Both the enhanced inherent barrier effect of epoxy coatings, the pH-responsive release behaviors of the PA inhibitors from crosslinked CPH network and the durable anodic protection effect of CPH are beneficial for improving the anti-corrosive performance of the epoxy coatings. It is believed that this kind of crosslinked CPH network will provide a new strategy for designing highly self-healing and anti-corrosive performance of epoxy coatings for the active corrosion control of other metals.