Size-Dependent Radiative Cooling Power of Glass-Polymer Metafilms

Abstract

Glass-polymer metamaterial, with glass microspheres randomly distributed in a polymer matrix, has been shown to be a highly efficient daytime radiative cooling material that can be roll-to-roll manufactured at scale and at low cost. In this work, we performed comprehensive study on the size effect on radiative cooling power of this hybrid metamaterial, including microsphere size, film thickness and the volume fraction of microsphere. It is unveiled that the net radiative cooling power of the metamaterial increases quickly with microsphere volume fraction and film thickness but gradually the increasing rate becomes small. In particular, the glass-polymer hybrid metamaterial film with a thickness down to 50 μm and having about 8% SiO2 microspheres possesses a uniform and strong emission across the entire atmospheric window. Regarding the microsphere size, the net radiative cooling power increases at first with the the microsphere size, then decreases slightly and finally reaches a steady platform level. Depending on the microsphere volume fraction and film thickness, the optimum microsphere radius ranges from 1.4 μm to 4.0 μm. This study provides a guidance of numerical calculations for designing similar thermal-control metamaterials.

Keywords: Glass-polymer metamaterial, radiative cooling, size effect, solar reflection, net cooling power