Structural Optimization of Radiative Cooling Nanocomposite Films for Clothing Applications

ABSTRACT Passive radiative cooling structures that combine enhanced solar reflectivity and higher emissivity have recently drawn attention. However, achieving efficient cooling performance critically depends on the structural optimization of both material composition and fabrication parameters. Herein, randomly distributed micro‐nano porous polyvinylidene fluoride (PVDF) nanocomposite films (PVDF‐ZnO) including zinc oxide (ZnO) nanoparticles were fabricated through non‐solvent induced phase separation (NIPS) method. A comprehensive optimization was carried out about film thickness, particle diameter, and concentration to obtain the necessary heterogeneous porous nanocomposite structure enabling enhanced mid‐infrared emissivity and solar reflectivity for passive cooling performance. Besides standard morphological and chemical analyses, emissivity and reflectivity characteristics were measured by FT‐IR and UV–VIS–NIR spectrophotometers with integrating spheres, respectively. Direct passive cooling performances were measured, and cooling power calculations were conducted under both simulated and real‐life conditions by a hotplate system including lamp and outdoor measurements in turn. Results demonstrate that ZnO incorporation within the porous film enhanced both emissivity (up to 94%) and reflectivity (up to 94%) for all production parameters. Accordingly, the maximum passive cooling performance was obtained for the nanocomposite film having 30 nm, 20% ZnO and 600 μm thickness according to hotplate test results compared to their nonporous form (7.73°C), bare skin (9.2°C), and cotton fabric (9.62°C). For the real‐life conditions, PVDF‐90ZnO20_400 had the maximum cooling performance; namely 17.1°C and 16.1°C under cloudy and sunny weather, respectively. The optimized nanocomposite structures gave promising results from a scalable production approach, making them ideal candidates for various clothing applications.