Preparation And Research Of Colorful Radiative Cooling Films

Radiative cooling is a new cooling approach which enables daytime cooling without consuming energy.The use of white radiative cooling materials is restricted owing to their nonaesthetic apperance.However,traditional coloring methods will significantly reduce the reflectivity of radiative cooling materials in the visible spectral range,then weaken their cooling capacity.In this dissertation,colored passive radiative cooling(CPRC)thin-films with high reflectivity in the visible spectral range and high emissivity in the mid-infrared spectral range was prepared.The three-dimensional photonic crystal structural color layer of polystyrene was self-assembled by gravity deposition on the surface of white functional film.The spectral properties and actual cooling capacity of the composite films were studied by characterization such as SEM and UV-VIS-NIR spectrometer and the homemade device.The mian work and results are as follows:(1)The relationship between the color and the size of PS nano-microspheres of the three-dimensional photonic crystal structural color films was calculated by modified Bragg equation theory.PS three-dimensional photonic crystal structural color films with face-centered cubic packing of different colors were fabricated by gravity sedimentation self-assembly method.The size of the nanospheres ranged from 223 nm to 278 nm,and the color of the films shifted to red as the particle size increased.The corresponding relationship between the microsphere size and color calculated by theory was consistent with the actual experimental result.(2)The influence of the proportion of aqueous polyacrylate(P(MMA-BA))binder on the properties of structural color films was discussed.It was found that when the ratio of PS to P(MMA-BA)binder was 10:1,the structural color films were stable and colorful and the PS nanospheres were stacked with few defects.(3)The influences of the filler content and thickness of the base film and the thickness of the PS structural color layer on the spectral properties of CPRC films were discussed.It was found that the CPRC film had better property when the filler content of the base film was70%,the wet base film thickness was 400?m,and the PS emulsion volume of surface layer was 0.70 ml/cm~2.(4)The cooling mechanism of the CPRC film was initially discussed.The three-dimensional photonic crystal structural color layers with different sizes of PS nanospheres interacted with visible light by interference and diffraction without absorbing to present different colors.The sunlight passing through the surface layer was reflected again by the bottom film to achieve high reflectivity in the solar spectral range.In addition,the bottom film provided high emissivity property in the mid-infrared spectral range.Then the excellent cooling performance of CPRC films was realized.(5)The cooling test results shown that the temperature of the green PS 3D photonic crystal structure-colored CPRC film was 3.50°C lower than the dye-colored CPRC film at noon.