Bioinspired materials for radiative cooling by biomimetic mineralization

Abstract Radiative cooling transfers thermal energy to outer space through the mid-infrared spectrum. Silica glass microspheres can create high-emissivity metamaterials. This study prepared mesoporous and silica-based bioglass particles due to strong phonon-polariton resonances of silica and used a biomimetic mineralization process to form calcium carbonate and hydroxyapatite nanoscale structures. These structures scatter and reflect sunlight effectively. Polyvinyl alcohol substrate, with infrared molecular vibration characteristics, formed an interpenetrating polymer network with micro/nano hierarchical structure powders for daytime passive radiation cooling. Characterization of biomimetic mineral coatings included: microstructures observation by field-emission scanning electron microscopy; phase identification by X-ray diffraction; Brunauer–Emmett–Teller surface area and pore size distribution measurement; solar reflectivity and infrared absorption measurement. Taguchi method is an experimental planning method that can handle multiple variables and levels at the same time. The optimized condition level based on Taguchi method can be evaluated as: particle size of 2 μm, mineral period of 3 days, mineral concentration of 50%, and powder concentration of 30%. The radiative cooling performance test outdoors results show that the biomimetic mineralized bioglass coating can reach a maximum temperature reduction of 27.4 °C compared to 304 stainless steel plate at noon by radiation cooling. Adaptive neuro-fuzzy inference system was also used to construct an artificial intelligence model to predict the biomimetic mineralized material optimize radiation cooling and applicability. If the local weather conditions are provided, the radiation cooling performance of the product can be predicted. This study showed bio-inspired materials for radiative cooling by biomimetic mineralization.