# Advanced Micro/Nanocapsules for Self-Healing Coatings
## 2 Self-Healing Coatings Based on Additives Including Corrosion Inhibitors
Studies based on the release kinetics of MBI from the CHSs proved that deposition of the released MBI molecules onto the metal substrate could be achieved. The mechanical and electrochemical evaluation of the produced coatings after their exposure to corrosive environments revealed enhanced active/self-healing/barrier properties as well as wet adhesion strength of the coating onto the metal substrate. [PERSON] and her team conducted experiments on the self-healing ability of epoxy coatings after incorporation of microcapsules loaded with highly reactive isocyanates [19] and polyethyleneimine [20]. Calcium carbonate microagglomerates, with an average diameter of 2.5 mm and consisting of several round-shaped nanoparticles, were synthesized and loaded with the corrosion inhibitor polyethyleneimine [20]. The pH-sensitive loaded microparticles were utilized as additives in epoxy coatings, which were applied to carbon steel via the dip-coating process. The obtained coatings were characterized with respect to their morphological, structural, and corrosion protective properties, and the results revealed that the modified coatings imparted enhanced corrosion protection as well as very stable barrier properties as the time elapsed. Moreover, the abovementioned coatings demonstrated improved self-healing properties. The corrosion inhibition effect was the result of the dissolution of calcium carbonate microparticles due to the pH variation, resulting in the subsequent release of the corrosion inhibitor. The outcome was the formation of a protective film on the steel's surface. Steel plate corrosion resistance after the application of epoxy-based coatings modified with microcapsules loaded with isophorone diisocyanate and with pH-sensitive cerium tri(bis(2-ethylhexyl))phosphate particles serving as inhibitors was also investigated by [PERSON] et al. [19]. The healing effects were assessed by a combination of several electrochemical techniques. The acquired results after the combination of both additives showed a multilevel protection effect that was characterized by more stable and enhanced coating barrier properties without any interfacial corrosion activity. The healing mechanism in the coating included hydroxyl ion accumulation, which significantly reinforced the corrosion protection conferred by the epoxy coating, providing stable corrosion protection over time. [PERSON] and his team reported the self-healing properties of epoxy-based polymeric nanocomposite coatings that were applied to steel substrates [21]. Both talc nanoparticles (TNPs) modified with sodium nitrate as well as microcapsules of urea-formaldehyde, including linseed oil, were embedded into these coatings. The efficient loading of NaNO\({}_{3}\) into TNPs, which can be attributed to the existence of a physiochemical adsorption mechanism, proceeded without affecting the TNPs' parent lamellae structure. The characterizations showed that the release of the NaNO\({}_{3}\) corrosion inhibitor from TNPs was influenced by the variations in the solution pH as well as the immersion time. Additionally, the release of the self-healing agent, i.e., the linseed oil microcapsules, in response to the external damage was estimated to be a time-dependent procedure. Promising corrosion inhibition efficiency and self-healing properties were achieved and were ascribed to the combination of inhibitors, nanocontainers, and self-healing agents. In a similar work by the same team, epoxy coatings were reinforced by the incorporation of cerium dioxide nanoparticles loaded with dodecylamine and n-methylthiourea as organic corrosion inhibitors [22]. The potential self-healing properties of the produced coatings as well as the increase in their lifetime were estimated. The CeO\({}_{2}\) nanoparticles displayed a pH-sensitive and self-releasing behavior of the corrosion inhibitors. The release of the inhibitors resulted in the formation of a protective layer on the defect sites of the steel surface and the corresponding healing effect.