Synthesis of polyaniline microcapsules for corrosion protection

Corrosion of metals is a serious problem that can be controlled by various methods. Polymer coatings can be used to protect metal surfaces against corrosion. During the time, these coatings are permeable to corrosive agents and also damaged by mechanical stresses, so recent studies are focused on self-healing coatings. The most common method is encapsulated self-healing agents in the polymeric layer as a shell. Controlling the release of active agents is carried out according to environmental conditions such as mechanical scratches, localized pH changes, and oxidation-reduction reactions. In most previous studies, the self-healing process occurs mainly after mechanical defects. However, the release of the self-healing agent with the reduction-oxidation response has used for specific applications such as corrosion protection. Among the numerous available polymers with redox properties, conductive polymers are significant because of their high electrical conductivity and excellent environmental and thermal stability. In this study, polyaniline (PANI) microcapsules were successfully synthesized by the oxidative polymerization of aniline in the direct miniemulsion method. The Field Emission Scanning Electron Microscopy (FE-SEM) was used to study the morphology of the surface of the microcapsules. Fig. 1 shows the FE-SEM images of the polyaniline microcapsules synthesized via miniemulsion polymerization. According to Fig. 1, the diameter of the spherical microcapsules was approximately 0.6- 1.2 μm. The chemical structure of the microcapsules was investigated using Fourier Transform Infrared (FTIR) spectroscopy. Absorption peaks appeared around 1130, 1286, 1494, and 1583 cm-1 in the FTIR spectrum of the microcapsules (Fig. 2) are associated with the C═N stretching, C─N stretching, and C═C stretching in the benzenoid and quinonoid rings, respectively. The results show that polyaniline microcapsules are in the form of emeraldine salt. The oxidation-reduction reaction between the benzenoid unit and oxygen in the polyaniline microcapsules, cause these particles to be an attractive choice to use in anti-corrosion and self-healing applications in metallic systems.