Self-healing Coatings Loaded by Nano/microcapsules: A Review

Coatings are applied on metallic surfaces to provide a dense barrier against the corrosive environment. However, coatings in most cases are vulnerable to damage in the form of internal cracks, which are difficult to detect and repair. One of the most promising types of smart multifunctional coatings is a self-healing coating, which has attracted interest in materials research due to its capability to prevent crack propagation by releasing healing agents at the site of cracks. These self-healing coatings demonstrate autonomic repair for internal cracks as they comprise a coating matrix and nano/microcapsules. Incorporating nano/microcapsules into the coating matrix ensures that the healing agent releases in reaction to propagation of cracks in the coating and then releases the self-healing characteristic to them. This paper aims to provide a perspective of this class of self-healing coatings that incorporate micro/nanocapsules and their synthesis methods. The emulsion method for the synthesis of capsules by organic and inorganic shells is covered as well as the most effective parameters which influence the size of nano/microcapsules. Finally, the incorporation of nano/microcapsules in the metallic and polymeric coating and the possible mechanisms of co-deposition have been presented.