Scalable and efficient radiative cooling coatings using uniform-hollow silica spheres

Radiative cooling technologies are being actively researched to achieve a more sustainable society by reducing greenhouse gas emissions due to the lack of energy input. A typical approach to improve radiative cooling performance is to deploy metamaterials as porous polymers with high reflectivity and high long-wave infrared emissivity. There is also a demand for research on coating materials for simple coating processes, but they have not been sufficiently studied as materials for radiative cooling. In this work, a hybrid radiative cooling material was fabricated using polydimethylsiloxane (PDMS) as a binder and mixed with hollow silica (SiO2) spheres. The fabricated hollow particles were compared to commercial hollow particles in film (radius 1.5 cm, thickness 2 mm) form for radiative cooling performance. The solar reflectance of the fabricated hollow particle film is 0.90, while the commercial hollow particle is 0.84, which realizes high-performance passive radiative cooling. In addition, the radiative cooling power of 122.66 and 98.89 W m−2 is achieved under direct sunlight, which is 7.6 ℃ and 3.3 ℃ lower than the ambient temperature. This study finds that the hollow silica film with uniform particles of 3um size outperforms the commercial hollow silica film in radiative cooling performance and offers the possibility of commercialization due to its light weight and easy fabrication process.