Hierarchically structured superhydrophobic composite films for efficient radiative cooling and energy saving

Abstract

Passive daytime radiative cooling (PDRC) is a sustainable strategy for lowering surface temperatures by maximizing solar reflection and efficiently emitting thermal energy in the mid-infrared range. However, the effective application of PDRC materials is frequently constrained by performance deterioration caused by surface contamination in real-world environments. In this study, we present a high-performance composite film that integrates superhydrophobic self-cleaning properties, exceptional radiative cooling capabilities, and effective thermal insulation. The film features a hierarchical micro/nanostructure, composed of porous polydimethylsiloxane (PDMS), micron-sized glass microspheres, and nanoscale hydrophobic SiO₂ particles. This structural design enhances the solar reflectance and infrared emissivity by leveraging the multi-scale roughness and porosity. The film achieves an impressive solar reflectance of 94.2% and an infrared emissivity of 95.6%. Additionally, it exhibits a water contact angle of 160°, showcasing exceptional superhydrophobicity. This synergistic design enables a subambient temperature reduction of up to 7.8 °C under direct sunlight. Moreover, the superhydrophobic self-cleaning properties effectively prevent surface fouling and wetting, ensuring long-term operational stability and efficiency. These characteristics make the composite film a promising candidate for advanced thermal management in applications such as electronics, vehicles, and building materials.