Robust polyurea/poly(urea–formaldehyde) hybrid microcapsules decorated with Al₂O₃ nano-shell for improved self-healing performance

Polyurea/poly(urea–formaldehyde)/Al₂O₃ hybrid microcapsules with a dense Al₂O₃ nano-layer containing 4,4′-methylenebis cyclohexyl isocyanate (HMDI) have been successfully fabricated via combaning Atomic layer deposition (ALD) process and interfacial/in-situ polymerization process. This dense Al₂O₃ nano-layer can be controllable deposited in the form of a single atom film through continuous self-limiting reactions of Al(CH₃)₃ and H₂O on the surface of the PU/PUF microcapsules at a temperature range of 120–180 °C. The formed hybrid microcapsules showed a monodispersed diameter of ~60 µm with a controlled and nano-sized Al₂O₃ shell. Moreover, the deposited Al₂O₃ nano-shell significantly increased the thermal stability and mechanical property of hybrid microcapsules, which could maintain their integrity under harsh conditions. In addition, by embedding hybrid microcapsules into an epoxy matrix, an excellent anticorrosion performance in scratched coatings via self-healing functionality was obtained. Therefore, the formed hybrid microcapsules with enhanced thermal stability and mechanical property via ALD process could promote their practical application in self-healing composites.