Simple preparation of PVDF composite flexible film with transparent, self-cleaning and radiative cooling properties†

Abstract

Daytime radiative cooling is a technique that relies on reflecting sunlight and radiating heat through mid-infrared wavelengths to cool objects. However, most daytime radiative cooling materials are not transparent, cannot be used for vehicle windows or other objects that need to retain their original color, and are susceptible to rain, dust, and other contamination, resulting in reduced cooling performance. Here, we developed a transparent, self-cleaning, radiative cooling, highly flexible PVDF composite film (PPF film), which was prepared by solvent evaporation phase conversion method and scraping coating method. The preparation method is simple and the material is easy to obtain. The obtained PPF film can be crimped to different degrees, has high flexibility, a transmittance of 94% in the visible light range (380–760 nm), and a water contact angle of 105° and above, and has self-cleaning performance. In the range of 8–13 μm, the average emissivity of the film reached 94.42%. Outdoor experiments show that, on sunny days, the cavity temperature of the device coated with PPF film glass decreases by 5–6 °C compared with that of bare glass, indicating that the PPF film has excellent radiative cooling performance. In addition, it has relatively strong mechanical properties, ultraviolet aging resistance and acid and alkali resistance. The design of the PPF film enables the radiative cooling material to be transparent, self-cleaning and flexible, with broad application prospects in the outer surface of objects requiring light transmission and cooling, such as special-shaped curved surfaces, solar panels, and architectural glass.