Hierarchical Micro-structured Polymer Film For Selective Radiative Cooling

With the rapid development of industry,demand for refrigeration is increasing,Traditional cooling systems consume tremendous amounts of energy and thus aggravate the greenhouse effect.More and more people begin to explore greener ways of thermal management.Radiative cooling is a passive cooling technology that radiates the heat through a transparent window of the atmosphere(8-13 μm)to the outer space.Radiative cooling has attracted extensive attention from researchers at home and abroad.Recently,a number of materials and structures with tailored spectrum have been demonstrated to achieve the effect of radiative cooling,such as wood fiber,polydimethylsiloxane,polyvinylidene fluoride.Micromachining can achieve better visible mid-infrared spectrum cutting,but this precision material processing method is limited by the manufacturing cost and preparation scale,the macro preparation problem is still an important bottleneck restricting its application.Here,we demonstrate that a hierarchically designed polymer film,produced by a scalable roll-to-toll electrostatic spinning process,enables selective mid-infrared emission,effective sunlight reflection and therefore excellent all-day radiative cooling performance.Specifically,the selective emissivity of the film is 78% in 8–13 μm wavelength range,and the design of nanofibres with a controlled diameter allows for a high reflectivity of 96.3%.As a result,the radiative refrigerant can be 5 ℃ lower than the ambient temperature in the daytime and 3 ℃ lower than the non-selective emission radiative refrigerant at night.With its excellent cooling performance and a scalable process,this hierarchically designed selective thermal emitter opens a new pathway towards large-scale applications of all-day radiative cooling materials.