Simultaneous\nEnhancement of Cooling Performance and\nDurability of the Polymer Radiative Cooler by a High UV-Reflective\nPolymer Multilayer Film

The\ndevelopment of polymer radiative coolers with easy processing,\nlow cost, and high inherent emissivity has significantly promoted\nthe industrialization process of passive daytime radiative cooling.\nFor excellent outdoor durability, however, the traditional strategy\nof using UV absorbers inevitably weakens the cooling performance of\npolymer-based coolers. The introduction of a high UV-reflective layer\nhas been proven to be the most effective strategy to eliminate the\nnegative effects of UV absorption and improve the durability of polymer\ncoolers. Here, a polymer multilayer film (PMF) based on an optical\ninterference mechanism is designed, which exhibits an average reflectance\nof up to 92.3% in the 300–400 nm UV wavebands. Using a TiO<sub>2</sub>-doped epoxy resin (TiO<sub>2</sub>-EP) cooler as an example,\nthe solar reflectance of TiO<sub>2</sub>-EP increases by 5.43% after\nintroducing PMF as a UV reflective layer. Outdoor tests without shading\nor convection coverage demonstrate that the average cooling temperature\nof TiO<sub>2</sub>-EP with PMF is further elevated by approximately\n1.1 °C. Additionally, its aging rate decreases significantly,\nand the solar reflectance is 5.08% higher than that of TiO<sub>2</sub>-EP without PMF after 120 h of UV aging experiments. Furthermore,\nPMF obtains a periodic multilayer structure by multilayer coextrusion,\nwhich has the advantages of low cost and the ability to be prepared\nover a large area. PMF is suitable for any type of polymer cooler,\nproviding an efficient method to further promote large-scale application\nof polymer coolers.