Scalable and flexible radiative cooling composite metamaterial structure with thermally responsive emissivity tunability

An ideal thermally adaptive composite metamaterial structure (CMS) requires precise spectral control capabilities to achieve efficient heat emission within the atmospheric transparency window (8–14 μm), scalability, and durability to facilitate effective thermoregulation in response to the ambient temperature. Here, we propose a polyethylene (PE) based composite metamaterial structure (PE-CMS) constructed by randomly distributed vanadium dioxide (VO₂) and indium tin oxide (ITO) particles within the PE matrix, forming a PE based composite metamaterial film (PE-CMF), which is deposited on the aluminium substrate. Utilizing the low infrared (IR) absorption property of PE, the phase transition property of VO₂ and the high IR scattering properties of ITO, we have developed temperature induced PE-CMS. This design enhances the overall IR absorption through the scattering effect of metallic VO₂ particles during the temperature-induced insulator-to-metal phase transition, together with the scattering of ITO particles. This enables the automatic switching of the thermal emittance from approximately 60 %–75 %, upon the metal-to-insulator transition temperature. This study provides a theoretical explanation of the mechanism by which metallic VO₂ functions as an IR absorber by efficiently trapping infrared radiation, leading to an extended optical path length within the polymer matrix. Furthermore, it explores the selection of the most suitable polymer matrix for optimizing emissivity modulation in response to temperature variations. Numerical simulations, along with indoor and outdoor field tests, are utilize to explore the adaptive thermal emission mechanisms underlying the proposed PE-CMS. The structure can be a promising structure for utilizing as a dynamic in various applications for adaptive thermal regulation.