Radiative cooling film with self-cleaning function

As a new type of refrigeration technique, radiative cooling can reduce the temperature of the object without consuming energy, thus, exhibiting a significant development prospect. However, due to the long-term exposure of the surface to the outdoor environment, the particles deposited on the surface affect the radiative cooling performance. In this study, a radiative cooling multilayer film with self-cleaning function has been proposed. The top surface has been designed and manufactured by employing a mixture of polydimethylsiloxane (PDMS) and SiO2 particles with different particle sizes and proportions to achieve the self-cleaning character. The bottom surface is composed of PDMS and Al films. Further, the transfer matrix method has been used in this study to optimize the combination and thickness of the bottom PDMS and Al films, and the FDTD method has been used to optimize the SiO2 particle size, volume fraction and coating thickness. Finally, the thickness of the bottom PDMS layer has been optimized to 40 μm, with the SiO2 particle sizes of 0.04 μm and 0.1 μm and the coating thickness of 40 μm, based on which the theoretical net cooling power calculations and experimental trials have been carried out. The calculation results show that the net cooling power can reach 59.04 W/m2 under the conditions of the American standard atmospheric model, and the difference in the net cooling power under the two different atmospheric model conditions is 24.36 W/m2. The experimental results also reveal that the maximum temperature of the object can be reduced by 2.1 °C during the day and 3.44 °C at night, with the maximum surface contact angle reaching up to 164.45°. In addition to the achievement of radiative cooling, the developed film possesses an optimal self-cleaning performance and can effectively reduce the maintenance cost during operation. In addition, the preparation process is simple and inexpensive, thus, exhibiting the high potential of real-life applications.