Water-Based Hydrophobic Paints for Daytime Radiative Cooling

Radiative cooling paints and coatings make for an effective and scalable approach to implementing daytime cooling. However, paints often contain volatile organic compounds (VOCs), which pose health hazards and harm the environment. Therefore, the negative effects of VOCs must be resolved to ensure full implementation of paints as a radiative cooling technology. In this study, single-layer and metal-free, water-based and hydrophobic BaSO₄, CaCO₃, and hBN radiative cooling paints are presented. These paints demonstrate full daytime subambient cooling of 2.7, 2.6, and 2.5 °C, utilizing their high solar reflectance of 95.4, 93.7, and 96.1%, and strong sky window emissivities of 0.932, 0.924, and 0.825, for BaSO₄, CaCO₃, and hBN paints, respectively. Hydrophobic properties yield high water contact angles of 118, 139.9, and 136.7° for BaSO₄, CaCO₃, and hBN paints, respectively. The paints achieve the low VOC classification by recording 26, 18, and 30 g/L of VOC content, lower than many commercial water-based paints with VOC contents of up to 200 g/L. This work presents environmentally friendly ultrawhite radiative cooling paints, which have the potential to reduce energy costs and combat climate change.