Durable Self-Cleaning Radiative Cooling Coatings for Building Energy Efficiency

Passive daytime radiative cooling (PDRC) is an energy-saving technology without an additional energy supply or environmental pollution. At present, most PDRC coatings for buildings are only aiming at high solar reflectivity (R_S) and high mid-infrared emissivity (E_MIR) while ignoring practicalities such as adhesion strength, scalability, and durability. In this work, modified calcined kaolin/(ethylene trifluorochloroethylene copolymer-polydimethylsiloxane) (MK/(FEVE-PDMS)) coating with super practicability is prepared by using MK as a filler, FEVE as an adhesive, and PDMS as a hydrophobic modifier. The R_S and E_MIR of the coating are 92.5 and 94.6%, respectively. The MK/(FEVE-PDMS) coating exhibits superhydrophobicity, with an advancing contact angle (ACA) of 160.2° and a hysteresis contact angle of 7.3°. At an average solar irradiance of 742.78 W m^-2, the coating achieved a temperature drop of 13.12 °C (shielded with PE film) and 3.09 °C (without shielding), respectively, relative to the environment. The coating adheres firmly to the substrate with an adhesion strength of class 2. The superhydrophobicity of the coating provides excellent durability and ease of repair, which can resist UV aging and mechanical damage. The durable superhydrophobicity gives the coating long-term stability in PDRC performance. Additionally, the cheap raw materials and the preparation process, consistent with the production of existing paints, show excellent scalability. Moreover, the energy consumption simulation results show that the energy saving ratio of the coating is more than 10% in the densely populated Yangtze River Delta and Pearl River Delta. The durable self-cleaning radiative coating developed in this work has potential application prospects in areas where the demand for cooling in summer is large and the demand for heating in winter is small.