Optimally Designed Multimaterial Microparticle-Polymer Composite Paints for Passive Daytime Radiative Cooling

Passive daytime radiative cooling(PDRC) devices have enabled subambientcooling of terrestrial objects without any energy input, offeringgreat potential to future clean energy technology. Among various PDRCstructures, random dielectric particles in a polymer matrix or paint-likecoatings have displayed powerful radiative cooling performances withexcellent scalability and easy fabrication. While modeling and analyzingsuch a system is nontrivial to enhance the cooling effect and engineerthe structures to be utilized in various applications, it is essentialto understand its complex physical relations and determine the optimaldesign conditions. In this work, we have thoroughly analyzed the opticalproperties and radiative cooling performances of PDRC paints composedof two-material particles (SiO2 and Al2O3) using 2D FDTD simulation and investigated the optimal designconditions. Specifically, we have studied the effects of design parameters,such as particle size, size distribution, binder volume ratio, andcoating thickness. Subsequently, we have conducted an outdoor coolingmeasurement of the fabricated PDRC paints to demonstrate their radiativecooling potential and to analyze and understand their performancebased on our numerical investigations. The fabricated PDRC paintsexhibited high solar reflectance (0.958) and strong long-wave infraredemission (0.937) in the atmospheric transparency window, achievinga maximum temperature drop of 9.1 & DEG;C. This comprehensive studyprovides a detailed characterization of the structure and materialparameters of the multimaterial PDRC paint system.