Flexible PPSU/Al 2 O 3 composite membranes with tailored microstructure: A new film for high-performance passive radiative cooling

Abstract The passive radiative cooling technology reduces ambient temperature without energy consumption. Nevertheless, existing material systems still suffer from complex fabrication processes and insufficient reflectivity. Herein, PPSU/α-Al 2 O 3 composite radiative cooling membranes were fabricated via evaporation-induced phase separation (EIPS). The incorporation of Al 2 O 3 nanoparticles modulated the pore structure and surface roughness of the membranes, thereby enhancing their optical properties. The measured membrane had an ultrahigh reflectance of 98.8 percent and an average emissivity above 0.97. Outdoor field tests demonstrated that the membrane achieves passive radiative cooling throughout the day, with a maximum decrease in temperature of more than 15°C relative to the substrate. Importantly, the PPSU/Al 2 O 3 composite membrane combines a straightforward, low-cost fabrication process with excellent flexibility, enabling direct application to curved surfaces.