Biomimetic Alumina\nFilm for Passive Daytime Radiative\nCooling

Abstract

Passive daytime radiative cooling is receiving more and\nmore attention\nas a cooling method that does not consume energy to cool objects.\nHowever, most radiative cooling materials require the mixing of multiple\nparticles, which increases the manufacturing process requirements.\nMost radiative cooling materials are susceptible to outdoor abrasion,\npollution, and UV exposure, which leads to decreased performance.\nIn this paper, the biomimetic film with both radiative cooling and\nself-cleaning functions was prepared by a simple evaporation-induced\nself-assembly process and spraying process using Al₂O₃ as the main radiatively cooling raw material, poly(vinylidene\nfluoride-<i>co</i>-hexafluoropropylene) [P(VDF-HFP)] as\nthe additive, and polydimethylsiloxane as the binder. Therefore, we\ncan get a biomimetic-Al₂O₃–P(VDF-HFP)-PDMS\nfilm (BAPPF). The BAPPF was spectrally selective. Specifically, the\nreflectance of BAPPF in the solar spectrum (0.45–0.89 μm)\nexceeded 100%, and the average reflectance in the main thermal effect\nof the solar spectrum (0.78–1.10 μm) was 99.92%. In addition,\nthe BAPPF had 96.97% reflectance in the solar spectrum (0.3–2.5\nμm) and 90.55% mid-infrared emissivity in the atmospheric window\n(8–13 μm). The combined performance enabled BAPPF to\nreduce temperature by up to 8.4 °C over air temperature in outdoor\ntests. What’s more, BAPPF had excellent superhydrophobic properties,\nwith a water contact angle of up to 159°. The self-cleaning of\nthe BAPPF prevented contamination and maintained cooling even when\nworking outdoors for long periods of time. Furthermore, the BAPPF\nmaintained high performance after mechanical friction, chemical corrosion,\nUV aging, and water impact, which has broad reference value and application\nprospects.