Fabrication of superhydrophobic P(VDF-HFP)/SiO2 composite film for stable radiative cooling

Abstract

Daytime radiative cooling that cools down an object by reflecting solar light and radiating heat simultaneously is expected to be a promising technology for dissipating heat without any energy consumption. However, radiative cooling materials’ solar reflection and infrared emissivity will be affected by the rain or dust pollution, therefore reducing the cooling performance under outdoor environments. A superhydrophobic radiative cooling composite film with hydrophobic SiO2 embedded in poly(vinylidene fluoride-co-hexafluoropropene) was proposed via phase separation technology. The SiO2 particles not only imparted to the film porous micro-nano tier rough structure to enhance the surface hydrophobicity, but also improved the mid-infrared emissivity of the film. As a consequence, the as-prepared film achieved 10.3 °C cooling under direct sunlight with convective heat reduced by transparent polyethylene film, and excellent superhydrophobicity with water contact angle greater than 160° and sliding angle close to 0°. Moreover, the cooling performance and superhydrophobicity of the film changed little after immersion in different pH solution and long-time exposure to UV irradiation. Importantly, the obtained film demonstrated great self-cleaning property making it hardly to be contaminated in outdoor environments, which is significant for sustainable applications.