关键词: 辐射制冷, 复合膜, 被动冷却, 反射, 红外辐射

Abstract: " Radiative cooling is a green, passive cooling technology that achieves temperature reduction through high solar reflectance and high mid-infrared emissivity in the atmospheric transparency window, characterized by “zero energy consumption and zero pollution”. Flexible composite films for radiative cooling have gradually become a hot research topic in this field due to their advantages such as lightweight, excellent flexibility and low cost. This paper summarizes the latest research progress on radiative cooling flexible composite films, describes the preparation methods and classifications of these films, points out their limitations, and provides an outlook on their future development. Firstly, the preparation methods of flexible composite films such as phase separation, electrospinning, freeze-drying, and spray coating are introduced. Among them, phase separation and electrospinning are commonly used methods for preparing polymer-based radiative cooling materials with excellent mechanical properties. The phase separation method has the advantages of simple operation, short processing time, and low cost. Electrospinning allows precise control over the diameter and distribution of nanofibers by adjusting parameters during the spinning process, thereby enabling the production of films with high solar reflectance. Freeze-drying can produce aerogel materials with a porous structure, which helps to improve solar reflectance. Secondly, flexible composite films can be classified into inorganic composite films, polymer composite films and multilayer composite films based on their material composition. Inorganic composite films are primarily obtained by incorporating inorganic particles with with high mid-infrared emissivity, such as SiO2, ZnO and TiO2. At the same time, by selecting the particle size of the inorganic materials, hierarchical structures with micro- or nano-scale features comparable to solar wavelengths can be constructed, inducing strong Mie scattering to achieve high reflectance and ultimately improve the cooling performance of the material. Polymer composite films mainly achieve infrared absorption and emission through the vibration of functional groups in the material, with functional groups such as C-O, C-Cl, C-F and C-N being suitable for solar radiative cooling. Multilayer composite films consist of a a macroscopic planar structure composed of multiple layers of different materials, typically including a solar reflection layer and an infrared emission layer. Additionally, the applications of these three materials in personal thermal management, energy-efficient buildings, food preservation, water harvesting, power generation, ice protection and agriculture are briefly discussed. Finally, the performance stability, durability and color diversity of composite films are analyzed, along with future development directions. Prospects for the further advancement of radiative cooling flexible composite films are also discussed."

Key words: radiative cooling, composite films, passive cooling, reflection, infrared radiation