Ordered Porous\nPolymer Films for Highly Efficient\nPassive Daytime Radiative Cooling

Abstract

Constructing porous polymer films for passive radiative\ncooling\nhas proved an efficient way to dissipate heat to cold outer space\nin the form of thermal radiation and concurrently reflect incident\nsunlight without additional energy input. Nevertheless, most researches\nfocus on randomly distributed pores, which cannot precisely control\nthe pore arrangement and size and may restrict the optical properties.\nHerein, an ordered porous poly­(methyl methacrylate) (PMMA) film comprising\nthree-dimensional (3D) ordered micropores and highly interconnected\nnanopores is presented via a sacrificial template method. It exhibits\nprominent solar reflectance (0.94), long-wave infrared (LWIR) thermal\nemissivity (0.95), and low thermal conductivity (0.044 W m^–1 K^–1). The ordered porous PMMA film can achieve\na sub-ambient temperature drop of up to 10.6 °C during midday\nunder an average solar irradiance intensity of ∼829 W m^–2 and promisingly realize a maximum daytime cooling\npower of ∼75.6 W m^–2. This work will significantly\ninfluence the design of porous structural radiative cooler and is\nconducive to understanding the underlying relationship between pore\narrangement, pore size, and optical/thermal performance, facilitating\nthe development of high-performance passive daytime radiative cooling\nporous polymer films.