Polymer coating with gradient-dispersed dielectric nanoparticles for enhanced daytime radiative cooling

Polymeric coatings with randomly distributed dielectric nanoparticles have attracted intensive attention in the passive daytime radiative cooling application. Here, we propose a modified Monte-Carlo method for investigating the spectral response and cooling performance of polymer coating with gradient-dispersed nanoparticles. Using this method, we carry out a quantitative analysis on the solar reflectance, infrared emittance and cooling power of four categories of gradient structures. It is shown that the gradient profile of particle distribution at the near-surface region has a significant influence on the overall performance of the coatings. Compared to a randomly distributed structure, the downward size-gradient structure exhibits superiority in both solar reflectance and cooling power. The presented gradient design, also applicable to porous structures, provides an effective and universal strategy for significantly improving the cooling performance of radiative cooling coatings.