Multiscale Multiphysics Simulation of hBN Thermal and Radiative Properties

Radiative cooling paint has emerged as a promising passive cooling technology with broad applications in energy saving, thermal management, and combating climate change. A thin layer, lightweight, and ultra-white hexagonal boron nitride (h-BN) nanoporous paint has been developed recently, but the underlying atomic level physics of its radiative cooling performance is not well understood. In this work, a multiscale, multiphysics computational framework is employed to predict its radiative cooling performance from the corresponding atomic structures. Leveraging first-principles calculations to study the electronic transitions and phonon dynamics, we predict the refractive index and extinction coefficients across solar and mid-infrared spectra. Subsequently, Monte Carlo simulation is used to study the photon transport in particle-matrix nanocomposites, which agrees with the experimental results of the solar reflectance and the sky window emissivity. By comparing with BaSO4-based paint, we explain the origin of the high solar reflectance at a lower thickness and the relatively lower sky window emissivity of h-BN paint.