Octagonal-siloxane based transparent and robust crack-healing surface for optical-scar recovery

Siloxane derivatives are a class of emerging hybrid materials that provide optical transparency and mechanically flexible characteristics owing to the low rotational barrier of the framework. To devise a robust and flexible self-healing platform, we designed an octagonal-siloxane derivative with four furan units and applied bifunctional maleimides as dienophiles to implement the reversible Diels–Alder (DA) reaction for crack healing. The feasibility of the DA reaction was confirmed by both the appearance of a cyclohexyl moiety in 1H-nuclear magnetic resonance spectra and heat transition behaviors during heating-cooling cycles in differential scanning calorimetry. The crack-healing efficiency of the designed octagonal-siloxane was sensitively affected by the heat-treatment temperature, and the crack recovery rate reached over 95% within 60 s upon heating at 100 °C. In addition, the crack recovery tendency was almost intact during repetitive heating-cooling cycles. The devised crack-healing film exhibited greater than 95% transparency in the entire visible region, and the effective modulus reached 7.8 GPa. In particular, when CdSe/ZnS quantum dots (QDs) were embedded into the octagonal-siloxane based film, it was confirmed that optical scars exhibiting luminescence defects were effectively recovered, and the emission characteristics of the QDs were not critically compromised even under solvent-exposed circumstances.