Achieving passive daytime radiative cooling via TiO$_2$/PDMS coating

Abstract: The exponential growth in population and the increasing global temperature trickles down to an explosive demand in cooling and refrigeration. The vicious cycle of carbon footprint generation by these cooling devices can be broken by a mechanism of passive cooling. This study outlines research undertaken with the aim to design such materials - exhibiting high reflectance in the solar spectrum and high emission in the atmospheric transparency window of 8-13 $\mu$m. The Monte Carlo (MC) method is used to simulate light propagation in a composite material aiding the design of metamaterials with these specific thermo-optical properties. A TiO$_2$/PDMS coating is fabricated to obtain > 91 \% solar reflectivity and > 75 \% emissivity in the atmospheric transparency window. This translates to cooling the coated body by 4-9 $^\circ$C below the ambient under peak solar irradiation in Mumbai, India. The facile fabrication process supplemented with the potential versatility of this coating shows promise to attain passive daytime radiative cooling on a commercial scale.