Hierarchically Superhydrophobic Stereo‐Complex Poly (Lactic Acid) Aerogel for Daytime Radiative Cooling

Abstract Passive radiative cooling technology provides a sustainable way of cooling by the combination of emitting heat to the cold universe and reflecting solar light without any energy input. However, the massive consumption of non‐degradable radiative cooling materials causes resource waste and environmental pollution. Meanwhile, the cooling efficiency can be easily affected by dirt contamination in outdoor environments. Here, by the combination of biomimetic hierarchical structure design and stereo‐complex crystals, a degradable and superhydrophobic (152°) stereo‐complex poly (lactic acid) aerogel with low thermal conductivity (37 mW m–1 K–1), high compression strength (0.1 MPa) and self‐cleaning ability via a simple water‐assisted thermally induced phase separation method is developed. The optimal aerogel has a high sunlight reflection (89%) and strong infrared emissivity (93%) that gets a temperature drop of 3.5 °C during the daytime and 5.8 °C during the nighttime. This aerogel opens an environmentally sustainable pathway to radiative cooling applications.