Cross-Linked Porous Polymeric Coating without a Metal-Reflective Layer for Sub-Ambient Radiative Cooling

Passive daytime radiative cooling provides cooling without energy input. This method is eco-friendly, which is beneficial, considering the increasing problems of global warming and urban heat islands. A poly(vinylidene fluoride) (PVDF) and polyurethane acrylate (PUA) matte white coating was prepared via photo-initiated free-radical polymerization. The porous polymeric coating without a metal-reflective layer exhibited an average emissivity of 0.9333 in the atmospheric window and an average solar reflectance of 0.9336 in the direct AM1.5 solar spectrum (888 W m^-2 in the 0.3-2.5 μm region). The radiative cooling power of the fabricated radiative cooler with a thickness of 518 μm was 94.2 W m^-2. Furthermore, the radiative cooler demonstrated radiative cooling performance during both daytime and nighttime in Seoul, Korea, and Chiang Mai, Thailand. The PVDF/PUA matte white coating without a silver reflector can prevent solar absorption caused by the oxidation of silver and reduce the light pollution caused by the metallic film because of the antiglare surface of the matte coating.