A nacre-inspired structural material with thermochromic properties and mechanical robustness by atomic-level design

Abstract Advanced structural materials are often required to exhibit a combination of lightweight, high strength, and superior toughness. Biomimetic strategies hold promise for achieving these seemingly conflicting mechanical properties simultaneously. However, current biomimetic structural materials lack active fire warning and passive flame retardant functionalities, which poses risks for their application in fire-prone scenarios. Herein, we present a nacre-mimetic alumina-cyanate resin composite (NAC) combining mechanical robustness with thermochromic and flame-retardant properties. Through controlled atomic doping, chromium atoms are incorporated into alumina micro-platelets, forming solid solution assembly units that exhibit reversible thermochromism and a solid solution strengthening effect. The bioinspired ‘brick-and-mortar’ structure endows the NAC with high strength (∼290.1 MPa) and fracture toughness (∼11.1 MPa m1/2). Coupled with a machine learning-based image recognition system, the NAC leverages its thermochromic properties to deliver a rapid fire warning within 9 seconds at 250°C, which is significantly faster than traditional electronic fire alarms. Its layered structure effectively impedes oxygen flow, achieving an oxygen limiting index of 50%, thus ensuring excellent flame-retardant performance. This design delays the combustion peak and reduces the heat release value, thereby enhancing the flame-retardant performance. This work demonstrates the effective integration of structural and functional design for active early fire warning and passive flame retardancy, paving the way for structural materials in advanced fire warning systems in challenging environments.