BaSO₄-Epoxy Resin Composite Film for Efficient Daytime Radiative Cooling

Conventional cooling methods are based on active cooling technology by air conditioning, which consumes a large amount of energy and emits greenhouse gases. Radiative cooling is a novel promising passive cooling technology that uses external space as the cooling source and requires no additional energy consumption. Herein, we propose an approach to prepare highly dispersed BaSO₄ nanoparticles (NPs) using a direct precipitation method combined with the in situ surface modification technology. The as-prepared PVP-modified BaSO₄ NPs with an average size of 20 nm can be stably dispersed in ethanol for more than 6 months and then were used as building blocks to prepare spherical BaSO₄ clusters with an average size of 0.9 μm using a scalable spray drying technique. The BaSO₄ NPs/clusters (mass ratio 1:1) were used for preparing radiative cooling epoxy resin film, showing a high solar reflectance of 71% and a high sky window emissivity of 0.94. More importantly, this composite film displays superior radiative cooling performance, which can reduce the ambient temperature by 13.5 °C for the indoor test and 7 °C for the outdoor test. Compared with the commercial BaSO₄ filled film, our BaSO₄-epoxy resin composite film offers advantages not only in radiative cooling but also in mechanical properties with a 16.6% increase of tensile strength and 40.1% increase of elongation at break, demonstrating its great application potential in the field of building air conditioning.