Ultrathin and High‐Efficiency Passive Daytime Radiative Cooling Coating via Polymer‐Particle Co‐Design

Polymer-based passive daytime radiative cooling (PDRC) coatings can mitigate global warming by reflecting solar radiation and emitting atmospheric transparency window (ATW) band mid-infrared (MIR) radiation into outer space (∼3 K). However, achieving high solar reflectance (R_sol) and MIR emissivity (ε_MIR) typically requires considerable thickness, which inevitably increases cost and self-weight. To fabricate ultrathin coatings with superior optical performance, we propose a polymer-particle co-design strategy that fully leverages their synergistic contributions. Specifically, polymers and particles containing functional groups with resonance frequencies matching those in the ATW are selected, while Lorenz-Mie scattering theory is employed to optimize particle sizes, thereby maximizing cooperative absorption in the ATW and complementary scattering in the solar spectrum. The resulting coating exhibits a high R_sol of 93.8% and a ε_MIR of 97.1%, while maintaining a thickness only 40% that of commercial coatings. Compared with commercial coatings, the proposed coating reduces unmanned aerial vehicles (UAVs) surface and simulated indoor temperatures by up to 8.1°C and 5.7°C, and achieves annual energy savings of 27.6, 24.8, and 22.6 MJ/m² in Haikou, Hong Kong, and Macau. These findings highlight the potential of this designed coating for UAVs thermal management and building energy conservation in low- and mid-latitude regions.