Scalable\nand Flexible Electrospun Film for Daytime\nSubambient Radiative Cooling

Abstract

Daytime\nradiative cooling materials reflect solar light and dissipate\nheat directly to outer space without any energy consumption, and thus,\nhave attracted much attention due to the potential applications in\nmany fields. Recently, elaborately designed photonic crystal and metamaterials\nhave been reported for daytime subambient radiative cooling. However,\nsuch materials and structures have the drawbacks of complex shapes,\ninflexibility, high cost, and limitation in scaling up. It is also\nextremely difficult to apply such materials to buildings, vehicles,\nand other objects having complex surfaces. Here, a scalable and flexible\nhybrid film for daytime subambient radiative cooling was fabricated\nby a facile electrospinning method. The hybrid film consists of poly­(vinylidene\nfluoride)/alumina (PVDF/Al₂O₃) fibers with diameters\nof 0.5–2.5 μm. Owing to the efficient scattering by fibers\nand Al₂O₃ nanoparticles, the hybrid film exhibits\nan extremely high average solar reflectance of 0.97. A high average\natmospheric window emittance of 0.95 is simultaneously achieved due\nto the molecular vibrations of PVDF and the phonon polariton resonance\nof Al₂O₃ nanoparticles. The composite film delivers\nan average net radiative cooling power of 82.7 W/m², and\na temperature drop of up to 4.0 °C under direct sunlight. The\nhybrid film exhibits remarkable radiative cooling performance under\ndifferent weather conditions including sunny, cloudy, overcast, and\nrainy. It can be used not only for cooling buildings and vehicles\nbut also for delaying the melting of glaciers. This work demonstrates\na promising method for scale-up production of the radiative cooling\nfilm with high performance.