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

Abstract 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 oC. 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.