Simple fabrication of a scalable, self-cleaning metakaolin-PDMS film for daytime radiative cooling

Passive daytime radiative cooling (PDRC) is a green, highly efficient, and energy-free technology, yet several challenges exist in its practical commercial implementation. In this work, a facile preparation method was employed to modify metakaolin (MK) into hydrophobic metakaolin (MMK). Using MMK as filler and polydimethylsiloxane (PDMS) as binder, a radiative cooling film (PDMS@MMK) with superhydrophobic properties was fabricated. Via this simple blending approach, a high solar reflectance of 90.2% and outstanding broadband long-wave infrared emissivity of 95.5% were achieved. Compared to an aluminum plate, this film produced an average temperature difference of 14.2°C on the surface of objects. When applied to model houses, model cars, or mobile phone cases, the film effectively lowered the temperature of these objects by 9–12°C under solar irradiation. Additionally, the film exhibited a surface contact angle of 151.5°, demonstrating excellent self-cleaning performance, along with feasibility for large-scale production. This study offers new insights into advancing PDRC technology toward multifunctional applications. • Uses low-cost clay for scalable, high-performance daytime cooling. • Combines superior daytime cooling with self-cleaning in a durable film. • Enables major energy savings in buildings and versatile applications.