Thermoplastic‐Polyurethane‐Based Foams via Water‐Assisted Thermally Induced Phase Separation for Daytime Passive Radiation Cooling

In recent years, global warming has been increasing, while conventional cooling devices remain inefficient and can emit greenhouse gases. The research and development of passive daytime radiative cooling (PDRC) are of utmost importance. Herein, a novel technique called water‐assisted thermally induced phase separation (WA‐TIPS) is employed to prepare thermoplastic polyurethane (TPU) foams with a hierarchical micro/nanostructure. By adding 2 mL of deionized water, the TPU foam achieves a solar reflectance of up to 95.5% and can provide a cooling effect of up to 7 °C during daytime, showcasing its significant potential for PDRC applications. Furthermore, leveraging the WA‐TIPS technique, the cooling performance of a composite foam consisting of TPU and SiO ₂ nanoparticles is investigated. Remarkably, it is discovered that incorporating just 0.1 g of SiO ₂ nanoparticles allows the composite foam to achieve daytime cooling of up to 15 °C. In this work, not only a novel approach for constructing micro/nanostructures is introduced but also a theoretical and experimental framework for advancing the development of polymer or polymer composite PDRC devices is established.