Tuning structures and properties of self-healing silsesquioxane films using block copolymers

Designing siloxane-based materials with self-healing properties is crucial for various applications. In this study, we report the preparation of organosiloxane-based thin films with a crack-healing capability, using 1,2-bis(triethoxysilyl)ethane ((EtO)₃Si-C₂H₄-Si(OEt)₃) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-type amphiphilic block copolymers. A lamellar mesostructure with alternating polymer and silsesquioxane layers (O_1.5Si-C₂H₄-SiO_1.5), featuring a periodicity of 9.56 nm, was formed through evaporation-induced self-assembly. The film exhibited reversible swelling behavior in response to changes in humidity. The cracks on the film disappeared immediately under humid conditions (90% relative humidity at room temperature). The nanoindentation hardness and elastic modulus of the film were higher than those of conventional lamellar silsesquioxane thin films prepared using a quaternary ammonium-type surfactant, which was attributable to the formation of thicker siloxane layers. Improved solvent resistance of the film was also confirmed by the fact that the mesostructure and crack-healing abilities were maintained even after immersion in ethanol. Thus the use of polymeric surfactants enhanced the mechanical properties and chemical stability of the mesostructured composites. These findings will lead to the development of self-healing siloxane-based coatings for various applications.