Two birds with one stone: insights into the micro-morphologies of SiO₂ spheres for simultaneously enhancing the fire safety and radiative cooling performance

Even though radiative cooling materials have demonstrated significant potential in decreasing energy consumption, pursuing higher efficiency and multi-functionality still remains a huge challenge. Herein, we first design four kinds of silicon dioxides (SiO₂) spheres that are widely explored and employed due to high infrared emissivity, to analyze the intrinsic mechanism between micro-morphologies and reflectivity properties. Besides, applicable to real application, we further add dendritic SiO₂ spheres with highest reflectivity into polyurethane (PU) resin, thus achieving an advanced PU-based film. Based on reflectivity of 95.5% and IR emissivity of 94.5%, the PU/dendritic SiO₂ composite film achieves sub-ambient temperatures of ∼7.9 °C and ∼7.3 °C, in nighttime and daytime, respectively. Attributed to its large specific surface and dendritic structure, SiO₂ spheres effectively suppress the escape of pyrolysis products that are further captured and converted into protective layer, by increasing melting viscosity. Consequently, the time and value of peak heat release rate in composite films are postponed by 13 s and decreased by 48.4%, respectively. In conclusion, based on “Two birds with one stone” strategy, this work provides a design thought for realizing the higher cooling efficiency and multi-functionality, thus significantly decreasing energy consumption and guaranteeing high fire safety in emerging buildings.