All-day radiative cooling with superhydrophobic, fluorine-free polydimethylsiloxane-embedded porous polyethylene coating

In this article, we introduce PolyCool, an all-organic, per- and polyfluoroalkyl substances (PFAS)-free coating designed for passive, all-day cooling applications. The coating utilizes porous polyethylene (PE), produced via a straightforward dip-coating and phase-inversion process, achieving a polydisperse pore size distribution that facilitates exceptional solar reflectance of 97.4%. To enhance its emissivity, polydimethylsiloxane (PDMS) particles synthesized through a green emulsification method, enabling scalable and size-controlled production, were incorporated. During a 36-hour continuous test in London, the developed coating achieved subambient temperature reductions of 2 °C under direct sunlight and 5.5 °C at night. These results were obtained without the use of convective shields, despite partial cloud coverage and humidity levels exceeding 40%. The radiative cooling potential of this coating has been estimated for 10 major European cities based on its spectral data and meteorological conditions. Additionally, the surface texturing of the coating enabled superhydrophobic properties, with a contact angle exceeding 160°. The coating also exhibited excellent ultraviolet (UV) resistance and can be applied to a range of substrates, including polymer films, aluminum foil, and wood, with minimal equipment and material costs.