Study on Preparation and Performance of Acid pH-Responsive Intelligent Self-Healing Coating

In this paper, microcapsules with acidic pH stimulus responsiveness were prepared through a one-step in situ polymerization method and a layer-by-layer assembly method. The effects of factors such as chitosan (CS) concentration, polymerization time, polymerization process temperature, and the number of polymerization layers on the performance of microcapsules were explored, and microcapsules with optimal performance were prepared and added to the epoxy coating. The morphology and structure of the microcapsules were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and zeta potential testing. The thermal stability and sustained release properties of the microcapsules were studied through thermogravimetric analysis and sustained release curve testing. Through scratch experiments, immersion experiments, salt spray experiments, and electrochemical impedance spectroscopy tests, the impact of the added amount of microcapsules on the self-healing performance and anti-corrosion performance of the coating in complex environments was explored. The results show that the optimal preparation process of acidic pH-responsive microcapsules requires that the concentration of chitosan is 2 mg/mL, the polymerization time of the polyelectrolyte layer is 8 h, the heating temperature during the polymerization process is 75 °C, and the number of polyelectrolyte layers is three. The prepared acidic pH-responsive microcapsules have good morphology, pH sensitivity, and thermal stability. The average particle size is approximately 203 μm, the drug loading rate reaches 59.74%, and the encapsulation rate reaches 63.99%. The optimal added amount of the acidic pH-responsive microcapsule coating is 15 wt%. The coating has a dual-trigger mechanism underlying it stimulus response capability and has an obvious stimulus response to acidic pH. It can inhibit corrosion in non-scratch areas, and its anti-corrosion ability is significantly stronger than that of epoxy coatings and ordinary self-healing coatings. The coating has a stronger repair effect and anti-corrosion ability when the environmental pH becomes acidic.