Polyborosiloxane-based Photonic Elastomers with Self-healing Capability

Recently, photonic crystals with short-range ordered structures have aroused extensive interest in scientific research owing to their structural color independent of angle variation. This unique property sets mateirals free from the angle-dependent color variation and plays a critical role in the practical applications involving color observation. However, such fascinating applications may be undesirably compromised by the poor durability of photonic crystals due to their delicate structures. In this study, we developed a series of polyborosiloxane-based photonic elastomers that possessed angle-independent structural color and self-healing capability. Specifically, hydroxyl-terminated poly(dimethylsiloxane) (Hydroxyl-PDMS) was reacted with boric acid (BA) by forming reversible dynamic covalent bonds, dative bonds, and hydrogen bonds, and as-obtained polyborosiloxane (PBS) elastomers were further incorporated with isotropically arranged SiO2 nanoparticles (NPs) and carbon black NPs. Optical properties of the photonic elastomers were characterized by reflection spectroscopy at varied detection angles, and angle independence was found for structural colors. Futhermore, the structural color of these elastomers could be tuned by simply adjusting the size or loading fraction of the SiO2 NPs in elastomers. The mateirals obtained had a Young's modulus up to similar to 200 kPa and also exhibited mechanochromic behavior thanks to the good flexibility of polymeric matrix. Moreover, the intriguing combination of flexibility with reversible bonding endowed the photonic elastomers with a rapid self-healing ability towards superficial scratches or cuts at room temperature, which in turn afforded the necessary durabilities both optically and mechanically. In addition, since photonic elastomer films with a large area could be readily fabricated through a simple spray-coating process, the materials developed have shown great prospects for applications in color-coating, displaying, sensing, and printing.