Nature-Inspired Bionic Leaves Showing Low Surface Temperatures upon Sunlight Irradiation

To overcome severe issues of photothermal effect from sunlight irradiation onto bionic leaves, natural-inspired bionic leaves with three layers, that is, high near-infrared reflection layer, absorption composite layer, and cilia layers are created. The front layer presents a high near-infrared light reflection and reduces photothermal effect from the sunlight. The mediate layer contributes to water transpiration and absorption, facilitating heat dissipation. The bottom layer has artificial cilia arrays that enhance air convection to reduce heat accumulation. More specifically, modified chromium trioxide (Cr₂O₃) is added into polyvinyl alcohol (PVA), and the optimal concentration is achieved based on investigations on photothermal effects. Carbon-fiber (CF) mat with calcium chloride (CaCl₂) is used as absorption composite layers. The water absorption and loss rates under different temperature and humidity are studied and fitted using different equations. Cilia arrays are created using a magnetic field induction method, and their heat convection effects are studied based on simulation. Finally, the three layers are assembled and their temperature reduction effects are studied. The results show that the average surface temperatures of tri-layered leaves are close to natural leaves andthe difference is 0.6 °C in a week.