Fabrication of Passive‐Cooling Janus Film Based on P( VDF ‐ HFP )/F‐ SiO 2 and PAA Hydrogel With Combined Effects of Evaporative–Radiative Cooling

ABSTRACT Radiative cooling achieves cooling by radiating heat into space, but the single radiative cooling effect is limited in practical applications due to atmospheric absorption and scattering. Hydrogel materials show potential in evaporative cooling due to their hygroscopic properties and flexibility, but they also face limitations such as water evaporation rate and ambient humidity. To address these issues, this study is dedicated to exploring novel radiative‐cooling materials. A radiative cooling layer composed of PFDTMS‐modified superhydrophobic SiO 2 and P(VDF‐HFP) is combined with a hydrogel formed by the mixture of choline chloride and acrylic acid, forming an enhanced interlocking structure and hydrogen bonds to enhance the interaction force. The hydrogel enables evaporative cooling during the day and moisture absorption for regeneration at night. The highest 和 of the bilayer film are 93.2% and 94.9%, and the cooling power reaches 110 W/m 2 . In a direct‐sunlight environment with an average solar power of 799.4 W/m 2 , the PAA‐P(VDF‐HFP)/F‐SiO 2 bilayer film can achieve a temperature reduction of 16.0°C relative to the ambient temperature. Moreover, the contact angle of the bilayer film is as high as 161.6°, endowing it with excellent self‐cleaning ability and enabling excellent and durable radiative cooling.