Passive cooling of buildings under sunlight can be achieved by enhanced coating reflectance. Embedding micro/nano-sized objects, such as nanoparticles, in a lossless material like a polymer, may serve the purpose of reflecting the desired spectrum. The knowledge of the behavior of pigments in the infrared region is therefore a critical factor in formulating coatings to specific requirements. Finite-difference time-domain (FDTD) simulations, which can simulate the propagation of electromagnetic waves in a medium, were here used to investigate the influence of nanoparticle additives on coatings reflection and to explore the corresponding working principles to reveal coatings with high level of reflectance. The numerical simulations demonstrate the reflective behavior in the coating material, showing that embedded titanium dioxide (TiO2) nanoparticles can significantly improve the reflectance of coatings with maximum values of around 0.9 in average and 0.7 in the infrared for 250 nm radius and 50% particle volume fraction. Furthermore, the reflectance improvement saturates around 100 mu m coating thickness. The numerical values are also shown to model experimental results.
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