Preparation And Performance Of One-Capsule Self-Healing Materials With SiO₂-Based Microcapsules

Functional polymeric materials have been widely used as anticorrosive, antifouling,and antimicrobial coatings as well as convenient protective and decorative coatings over the past decades. Particularly, advanced functional polymer composite coatings onto spacecrafts as the protective barrier, vital for the reliable operation of spacecrafts in orbits,have been drawn great attention due to many advantages such as the light weight, the tunable flexibility, and the easy processability. Unfortunately, the harsh space environment factors such as atomic oxygen, charged ions, thermal cycling, space debris and ultraviolet radiation commonly induce unavoidable microcracks formation of the surface coatings onto spacecrafts during the long-term flight. What is more, these microcracks are difficult to be detected and repaired in time, and may further extend to macrocracks and even larger cracks, which lead to the failure of the protective coating and to the ultimate reduction in the operating life and safety of spacecrafts. Introducing self-healing strategies into coatings opens up a great opportunity to enhance significantly the lifetime of the functional coating onto spacecrafts in orbits and to largely prolong the maintenance intervals, thereby promoting spacecraft availability and reducing maintenance cost. And the synthsis of microcapsules for self-healing coating became the core of this technology.Firstly, SiO2-based stable microcapsules containing epoxy resin(E-51 and A1815)were first synthesized successfully by an improved in-situ method. The deposition thickness of microcapsules could be finely tuned by regulating the concentration of aqueous HCl solution and the mass radio of core oil mixture and TEOS through the alternating electrostatic layer-by-layer assembly between protons and negatively charged silica oligomers. In addition, the stirring speed affected the size of the microcapsules.When the stirring speed was increased from 600 rpm to 1500 rpm, the particle size increased from 10 μm to 52 μm, which is concerned to the shearing of stirring paddle.With the improved in-situ method, we also prepared microcapsules respectively containing dimethyl siloxane and acrylic resins, which proved the universal applicability of this method.Secondly, monodisperse SiO2-based hybrid microcapsules simultaneously containingepoxy resin(E-51 and A1815) and cationic photoinitiator(PI6992) were first synthesized successfully by an improved in-situ method. The microcapsulated one-component self-healing system displays chemical and thermal stability and high repair efficiency for potential aerospace application. Chemical and thermal stability could be ascribed to the selected UV-induced adhesive providing with the performance of high bond strength and excellent mechanical properties. Additionally, high repair efficiency could be attributed to the homogeneous distribution of healing agent and photoinitiator before releasing. When the coating is damaged, healing agent and photoinitiator releasing from the broken microcapusules could repair microcracks in the presence of UV light.