Novel self-healing material for potential application in space coatings

UV-responsive single-microcapsule self-healing systems exhibit considerable potential to effectively repair the microcracks and then extend the service life and reliability of polymeric composite coatings on spacecraft because of abundant UV irradiation in space environment and the stable healing process based on an accurate stoichiometric ratio.

Unfortunately, UV irradiation in space environment also could cause undesirable curing of healing agents in the microcapsules embedded into the coatings before the generation and UV-responsive self-healing of the microcracks in these coatings and therefore deactivation of healing agents.

Good self-healing capability

Scientists now propose a UV-responsive single-microcapsule self-healing system with epoxy resin core and enhanced UV-shielding SiO₂/ZnO hybrid shell for polymer coatings through a layer-by-layer deposition strategy. Homogenous embedment of ultrasmall ZnO nanocrystals into the mesoporous SiO₂ shell endows the microcapsules with excellent UV-shielding performance. Moreover, in contrast to conventional polymer shell, a stable inorganic SiO₂ counterpart could avoid the degradation fate catalysed by photo-responsive ZnO or TiO₂ nanoparticles, thereby enhancing the stability of the microcapsule.

When the SiO₂/ZnO microcapsules after aging up to 21 days under UV radiation were embedded in the epoxy coating, the epoxy coating containing these aged microcapsules still displays good self-healing capability upon scratching and UV-induced self-healing, and then scratches are still filled and repaired, attributing to the shielding ability of ultrasmall ZnO nanocrystals highly dispersed into the SiO₂ shell from undesirable UV-induced curing of epoxy resin core before self-healing behavior in the UV-sufficient space environment.