Ordered Porous Polymer Films for Highly Efficient Passive Daytime Radiative Cooling

Constructing porous polymer films for passive radiativecoolinghas proved an efficient way to dissipate heat to cold outer spacein the form of thermal radiation and concurrently reflect incidentsunlight without additional energy input. Nevertheless, most researchesfocus on randomly distributed pores, which cannot precisely controlthe pore arrangement and size and may restrict the optical properties.Herein, an ordered porous poly(methyl methacrylate) (PMMA) film comprisingthree-dimensional (3D) ordered micropores and highly interconnectednanopores is presented via a sacrificial template method. It exhibitsprominent solar reflectance (0.94), long-wave infrared (LWIR) thermalemissivity (0.95), and low thermal conductivity (0.044 W m(-1) K-1). The ordered porous PMMA film can achievea sub-ambient temperature drop of up to 10.6 & DEG;C during middayunder an average solar irradiance intensity of & SIM;829 W m(-2) and promisingly realize a maximum daytime coolingpower of & SIM;75.6 W m(-2). This work will significantlyinfluence the design of porous structural radiative cooler and isconducive to understanding the underlying relationship between porearrangement, pore size, and optical/thermal performance, facilitatingthe development of high-performance passive daytime radiative coolingporous polymer films.