A novel aqueous scalable eco-friendly paint for passive daytime radiative cooling in sub-tropical climates

Abstract

Passive daytime radiative cooling (PDRC) is an emerging technology that dissipates heat from terrestrial objects to the cold universe directly via the atmospheric transparency window. Along with the advancement of PDRC materials, fabrication methods by precision lithography or phase change chemistry are no longer a preferred option due to the concomitant hazardous organic solvents. Instead, it is desirable to develop radiative coolers by aqueous processing-based and cost-effective methods so as to promote their mass production and applications. Herein, we report a new scalable polymer-based aqueous paint without volatile organic compounds (VOCs) emission. By using the simple mechanical agitation-based synthetic method with mixing polymer emulsion as the matrix and glass beads as the functional additive, the cooling paint exhibits an average infrared emissivity of 92% and a solar reflectivity of 94%. A detailed field experiment was conducted in sub-tropical climates to verify the practical cooling performance of the developed cooling paint, and the experimental results showed that the achievable sub-ambient cooling temperature was up to 6 °C under high humidity conditions without any solar shading or convection cover. Meanwhile, in-depth evaluation on the cooling power of the developed cooling paints in a variety of cities was conducted, which shows its wide application potential in building roof across varying climate regions.