Radiative Cooling Properties of Compressed SiO₂/PE Aerogel Composite Films

A passive daytime radiative cooling thin film material has been developed to provide the cooling source which requires no input, sustainable, and no pollutants or greenhouse gases emission. The thermally induced phase separation method and simple compression were used to prepare the compressed composite silica dioxide/polyethylene(SiO₂/PE) aerogel films. The impact of SiO₂ particle sizes and additions on the optical properties of composite films was investigated, and the internal microstructures and optical properties of the films were characterized. The optical properties of the films were enhanced by controlling the degree of compression. The results indicate that the addition of micro SiO₂ is more favorable for increasing reflectance and nano SiO₂ is more favorable for increasing emissivity, and the densification could result in emissivity enhancement and reflectance reduction. The optimal sample is achieved when the mass ratio of nano SiO₂ to micro SiO₂ to polyethylene is 0.5∶1∶1 and the compression ratio is one-ninth. This sample has a thickness of 0.5 mm, with 96.4% average reflectance of the solar spectrum and 95% average emissivity of the atmospheric window. The practical application performance of the sample was evaluated by testing its radiative cooling performance, antifouling and mechanical stability abilities. The experimental results show that the optimal sample achieves a significant temperature reduction of up to 6.5 ℃ compared to the sub-environment. This indicates that the SiO₂/PE aerogel film has the ability to passively cool the sub-environment during both day and night, and that it has a contact angle with water of 127°, providing water resistance and potential self-cleaning properties in practical applications.