Superhydrophobic and Flame-Retardant Poly(vinylidene Fluoride-co-hexafluoropropylene)/SiO2/Aluminum Phosphate Composite Film for Daytime Radiative Cooling

Radiative cooling technology has major benefits for energy-free thermoregulation since it can chill items without using any energy. However, the cooling efficacy of radiative cooling materials is hampered by outdoor pollution as well as a number of safety issues involved in practical applications, in particular, the fire hazard of polymer-based materials. Here, a porous composite film was created and manufactured that is flame-retardant, radiative cooling, and superhydrophobic. The average infrared emissivity of the film reached 97.2% with an average solar reflectance up to 98.4%. It produced subambient cooling in an outdoor environment, with an average temperature decrease of 11.5 °C. With a sliding angle of 3.6° and a water contact angle of 158.7°, the surface of the film exhibits conventional self-cleaning properties and is superhydrophobic. Notably, the film is flame-retardant with a limiting oxygen index of 38.3%, which is suitable for cooling materials with fire safety requirements.