Passive daytime radiative cooling with thermal energy storage using phase change n-octadecane/SiO2 nanobeads

In this study, a simple, facile, and high-performance passive daytime radiative cooling (PDRC) coating was developed by employing phase change n-octadecane/SiO2 (P–SiO2) nanobeads (NBs) for dual thermal management of both daytime radiative cooling and thermal heat energy storage. Monodisperse P–SiO2 NBs were synthesized via emulsion polymerization and were reversibly melted and crystalized at the phase change temperature of n-octadecane, which was used as a core phase change material (PCM). PDRC coating was fabricated by simple spray coating of P–SiO2 NBs/polymer solution on a glass substrate. Owing to the presence of the light-scattering air voids in the porous core-shell structure and the vibronic absorption of Si–O bonding in SiO2 NBs, the PDRC coating exhibited high reflectivity of 91.8% in the solar spectrum and high emissivity of 95.5% in the atmospheric window. We systematically investigated the influence of PCMs on thermal behavior by monitoring the PDRC coating under heating and cooling processes using infrared thermal imaging. We confirmed that the PCMs in the PDRC coating can effectively reduce the temperature of the coating by storing the thermal energy via the phase change process. During the daytime, the PDRC coating exhibited a temperature drop of 9.0 °C with average solar irradiation of 894 W/m2, which indicates that the designed PDRC coating is highly effective for radiative cooling.