Radiation-cooled aramid composite films featuring tunable TiO2 nanorod arrays anchored on the surface of 2D mica nanosheets for passive daytime radiative cooling applications

Abstract

Radiation-cooled films with the required high solar reflectance and emissivity as well as environmental durability are challenging to develop for passive daytime radiative cooling (PDRC) applications. Herein, an inorganic dielectric scatterer, producing strong scattering in the visible to near-infrared wavelength band, has been constructed by tunable TiO₂ nanorod arrays with a high refractive index on the surface of 2D Mica nanosheets with good mechanical strength and chemical stability. Subsequently, radiation-cooled aramid composite films featuring a well-organized 2D layered stack structure of inorganic scatterers were developed for PDRC applications. Due to the featured inorganic scatterers effectively stimulating multi-level scattering of light through TiO₂ nanorod arrays and multi-layered Mica structures, the radiation-cooled aramid composite films have ultra-high reflectivity of 97.5% and emissivity of 96.3% in sunlight, and achieve subambient cooling of 8.62 °C for daytime and 4.84 °C for nighttime. Meanwhile, the well-organized lamellar PDRC films possess high strength (98 MPa) as well as excellent environmental durability, including scratch-resistance, UV radiation-resistance and flame retardance, suggesting their great potential in PDRC for thermal regulation.