Superhydrophobic porous film for daytime radiative cooling

Passive daytime radiative cooling (PDRC) offers a sustainable way without additional energy input to cool objects by simultaneously reflecting sunlight and radiating heat through mid-infrared wavelengths. However, PDRC materials are easily contaminated by rain water, settled dust, microorganisms etc., which cause degradation in the cooling performance. Herein, we developed a porous composite film of ethylene-propylene-diene copolymer (EPDM) and hydrophobic SiO2 particles integrating superhydrophobic self-cleaning and radiative cooling. The film consists of EPDM micropores filled with numerous SiO2 agglomerations, resulting in solar reflectance of 96% with an average emissivity of 95% and superhydrophobicity with water contact angle of 162° and sliding angle of 1.2°. The film achieved a sub-ambient temperature drop of 12°C in sealed air and 7°C in open air under direct sunlight. Importantly, the superhydrophobic self-cleaning effect of the film prevents its surface from outdoor contamination or wetting, favoring long lasting cooling efficiency, which is promising in applications for cooling electronic devices, vehicles, building materials, etc.