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

Abstract

Passive daytime radiative cooling (PDRC) devices have enabled subambient cooling of terrestrial objects without any energy input, offering great potential to future clean energy technology. Among various PDRC structures, random dielectric particles in a polymer matrix or paint-like coatings have displayed powerful radiative cooling performances with excellent scalability and easy fabrication. While modeling and analyzing such a system is nontrivial to enhance the cooling effect and engineer the structures to be utilized in various applications, it is essential to understand its complex physical relations and determine the optimal design conditions. In this work, we have thoroughly analyzed the optical properties and radiative cooling performances of PDRC paints composed of two-material particles (SiO2 and Al2O3) using 2D FDTD simulation and investigated the optimal design conditions. Specifically, we have studied the effects of design parameters, such as particle size, size distribution, binder volume ratio, and coating thickness. Subsequently, we have conducted an outdoor cooling measurement of the fabricated PDRC paints to demonstrate their radiative cooling potential and to analyze and understand their performance based on our numerical investigations. The fabricated PDRC paints exhibited high solar reflectance (0.958) and strong long-wave infrared emission (0.937) in the atmospheric transparency window, achieving a maximum temperature drop of 9.1 °C. This comprehensive study provides a detailed characterization of the structure and material parameters of the multimaterial PDRC paint system.

Self-sustained and Insulated Radiative/Evaporative Cooler for Daytime Subambient Passive Cooling

“…RC materials exchange heat with outer space efficiently due to the enormous temperature difference between outer space and the Earth’s surface (3 K vs 300 K). − Moreover, by regulating the surface spectra, RC materials can avoid heating by atmospheric irradiance and reflect most of the sunlight. − EC uses latent heat from the gas–liquid phase transformation. Hydrogen bonds are formed between adjacent hydrogen and oxygen atoms in liquid water, endowing water with the highest enthalpy of evaporation among regular-temperature liquids. , …”

Highly Optically Selective and Thermally Insulating Porous Calcium Silicate Composite SiO2 Aerogel Coating for Daytime Radiative Cooling

“…At present, it has been pointed out that passive radiative cooling coating require a combination of multiple fillers to achieve synergistic effect for improving PDRC performance. 36−39 Yun et al 40 analyzed the optical properties and radiative cooling performances of PDRC paints composed of two-material particles (SiO 2 and Al 2 O 3 ) using 2D FDTD simulation, and the fabricated PDRC paints exhibited high solar reflectance (95.8%) and strong long-wave infrared emission (93.7%) in the atmospheric transparency window, achieving a maximum temperature drop of 9.1 °C. The advantage of the synergistic effect of different functions of multiparticles is to play the unique properties of various fillers, such as high emissivity of atmospheric windows, high reflectivity of sunlight, hydrophobic pollution resistance, multicolor, and so on.…”

“…The existing reports of radiative cooling coating based on individual particle mainly focus on the selection and optimization of the particle types, sizes, size distribution, , and other factors, but these methods cannot improve multiple performance parameters of radiative cooling coating. At present, it has been pointed out that passive radiative cooling coating require a combination of multiple fillers to achieve synergistic effect for improving PDRC performance. − Yun et al analyzed the optical properties and radiative cooling performances of PDRC paints composed of two-material particles (SiO 2 and Al 2 O 3 ) using 2D FDTD simulation, and the fabricated PDRC paints exhibited high solar reflectance (95.8%) and strong long-wave infrared emission (93.7%) in the atmospheric transparency window, achieving a maximum temperature drop of 9.1 °C. The advantage of the synergistic effect of different functions of multiparticles is to play the unique properties of various fillers, such as high emissivity of atmospheric windows, high reflectivity of sunlight, hydrophobic pollution resistance, multicolor, and so on. − In order to further improve the performance of PDRC, especially the thermal conductivity, it is an important way to improve the performance of PDRC by improving the thermal insulation performance of the coating through the synergistic effect of different functions of multiple particles.…”

Ordered Porous Polymer Films for Highly Efficient Passive Daytime Radiative Cooling

“…Several passive radiative cooling strategies, including photonic structures, − polymer-coated metal structures, , porous polymer films, − white paints, − structural woods, and textiles, − have been reported. Among all PDRC technologies, the fabrication of polymer films with abundant light-scattering nano/microscale air voids seems to be a highly efficient and cost-effective way, which manifests high solar reflectivity and thermal emittance as well as lightweight, durability, and industrial applicability .…”