| The proportion of building cooling energy consumption to global total energy consumption has been increasing year by year,causing many energy,environmental and economic problems.Considering this serious situation,a"zero-energy,pollution-free"radiative thermal control technology is constantly gaining people’s attention:By means of thermal radiation,heat could be continuously released into outer space（-270℃）through the atmospheric window,thus the radiator could continuously reduce the surface temperature,reaching a lower value than that of the non-radiative objects under the same circumstances or even the surrounding environment.An object usually gets heated to higher temperature due to the absorbed solar light at daytime.In order to achieve the radiative cooling effect at daytime,it is also necessary for a radiator to simultaneously achieve high reflection of sunlight.Under the natural law of survival of the fittest,after hundreds of millions of years,many species have evolved to have complex and delicate microstructures to effectively achieve light or thermal regulation.Investigating and mimicking the exquisite microstructure of natural species offers a new way for the preparation of high-efficiency radiative thermal regulation hybrid membranes.This project focuses on the optical characteristics of the yellow wings of Delias Agostina.By mimicking and modifying the sophisticate fine structure of wing scales,we successfully design and fabricate a high-performance hybrid photonic structure flexible membrane,and study its radiative thermal regulation performance.The main findings of this project are as follows:（1）By micro-morphological characterization,spectral characterization and simulation,it is proved that the"framework-nanobead"microstructure of the yellow scale is a bifunctional photonic structure that can effectively achieve high absorption or high reflection within specific wavelength bands.Then,under the guidance of the"deconstruction-reconstruction"bionic design concept,the FDTD simulation software is used to continuously simplify and optimize the relevant parameters of the original structural unit（such as shape,dimension,component,etc.）.The original"cross chitin framework+pterin nanobeads"biological model is transformed into"directionally aligned PVDF/TEOS porous fibrous framework+Si O2microspheres"bioinspired hybrid photonic model,so that the high reflectance and high absorption bands are extended and shifted from the original 550nm-800nm and 400nm-550nm to 250nm-2500nm solar band and 8μm-13μm atmospheric window,to achieve radiative cooling.（2）By electrospinning PVDF/TEOS framework and subsequent Si O2microspheres deposition,the bioinspired radiative thermal regulation hybrid membrane is prepared on a large scale and at low cost.Due to the relative high stack density of polymeric fibers,the membrane exhibits high strength while maintaining excellent flexibility.Spectral characterization shows that the 300-μm-thick membrane,even without any metal coating,reflects about97%solar light,and has an extremely high average emissivity>0.96 in the atmospheric window.A self-made device is used to test the radiative cooling performance of the membrane.The results show that the membrane achieves a sub-ambient temperature drop of about 10°C almost overnight.At noon when the sunlight intensity even exceeds 1000 Wm-2,the membrane still achieves a sub-ambient temperature drop of about 6°C.The average cooling power of the membrane at nighttime and daytime are 80Wm-2,61 Wm-2,respectively.Further calculation shows that the practical radiative cooling performance of the membrane is influenced by external factors such as ambient temperature,humidity and thermal insulation of the testing device,indicating that the membrane could exhibit higher radiative cooling performance if the experiments could be done on a more ideal condition.The radiative thermal regulation membrane prepared in this project has supreme performance while with low cost,and is expected to be put into practical application.Meanwhile,this project confirms the efficiency of the bionics design,and provides a new design strategy for the preparation of novel high-performance low-cost radiative thermal regulation devices. |
