Scalable and simply-fabricated paint for waterproof and passive radiative cooling

Abstract

Radiative cooling paint (RCP) has aroused great interest because of its high cooling performance and the simple processing process. However, the large-scale application of RCP is still limited by its poor cooling durability, which is related to a contaminated surface outdoors. Here, we proposed a superhydrophobic thermoplastic urethane (TPU)/BaSO₄/SiO₂ paint with a water contact angle of 150.6° that remained a sustainable clean surface to maintain its excellent cooling effect. The high electron band gap of BaSO₄, the appropriate and broad particle size distribution, and the abundant TPU/BaSO₄/SiO₂ interfaces dramatically promoted its sunlight reflectivity to 94.3 %. With the phonon resonance of BaSO₄ and SiO₂ at 9 μm, and the chains asymmetrical stretching resonance of TPU, the TPU/BaSO₄/SiO₂ coating reached a high IR emissivity of 93.9 %. Field tests indicated that the optimized TPU/BaSO₄ coating cooled the substrate by 24.3 °C, and the sub-ambient cooling effect reached 13.2 °C. Besides, the cooling power of the TPU/BaSO₄ membrane reached 108.8 W/m² at high noon and exceeded 200 W/m² when the temperature difference between the object and surroundings reached 20 °C. Additionally, the IR emissivity of the TPU/BaSO₄/SiO₂ coating remained 84.7 % even at an incident angle of 80°, so the cooling effect preserved a whole day. Our work provided a new design for high-performance passive radiative cooling materials with outstanding waterproof and self-cleaning properties.