Passive radiative cooling (PRC), an energy-free cooling method, has been ingeniously exploited to enable certain natural organisms to withstand extreme hot climates and has inspired numerous bionic designs. However, improving the durability of designed materials in real-life scenarios while inheriting nature's biological principles is a major challenge. After discovering the superior thermoregulatory capabilities of the inner surface of the Hawaiian scallop shell, we demonstrate a bionic dual-scale structure (BDSS) film for efficient passive radiative cooling with robust durability. We found that the inner surface of the shell consists of large-scale triangular ridges interspersed with small-scale terrace steps. This dual-scale structure can enhance the reflectance of sunlight through efficient Mie scattering and increase photon propagation, thereby increasing the emissivity in the mid-infrared range and thus lowering the surface temperature. Based on this discovery, we developed a BDSS film featuring a strong solar spectral reflectance of 0.95 and a high mid-infrared emissivity of 0.98, achieving sub-ambient cooling of 10.8°C under direct sunlight. Additionally, the designed film possesses strong durability, including excellent self-cleaning, flexibility, mechanical strength, chemical stability, and UV protection, making it promising for thermal temperature regulation in various harsh scenarios.
Bionic dual-scale structured films for efficient passive radiative cooling accompanied by robust durability
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