A self-cleaning nanoparticle polymer hybrid cooling film in humid environment

Passive daytime radiative cooling (PDRC) technologies that both reflect sunlight and pump heat out of objects on Earth into cold outer space, have attracted considerable attention in recent years. However, conventional PDRC materials face numerous limitations, including costly and complex fabrication methods, as well as performance losses due to surface contamination and humid climates. Here, we present a new radiative cooling structure consisting of a hydrophobic SiO2 nanosphere top layer, a polymethyl methacrylate (PMMA) middle layer, and a metallic Ag bottom layer. The hydrophobic SiO2 nanospheres layer provides a low surface energy nanoscale textured surface for self-cleaning, with a maximum surface contact angle of 151 degrees. The as-prepared film has a high solar reflectivity (similar to 96.6 %) and a strong broadband infrared emittance (similar to 88 %). The calculated net cooling power at 27 degrees C can reach 106.9 W.m(-2) and the predicted subambient cooling is 15 degrees C at night and 10 degrees C during the day in the dry environment. The outdoor experiments are carried out in a hot and humid city (Xiamen, China) and realize a promisingly subambient cooling of similar to 6 degrees C at night and even similar to 3.5 degrees C during a sunny summer day. These findings could have a substantial impact on energy consumption habits in hot and humid regions around the world. (C) 2022 Elsevier B.V. All rights reserved.