| With global warming,in the hot summer,people urgently use air conditioners to obtain a comfortable living environment.Compared with traditional cooling methods that require power input,radiative cooling is a new,low-power,pollution-free technology that does not require any power input and output,making it more attractive.The currently used radiative cooling materials still have problems such as complex preparation process,high production cost,and difficulty in large-scale application.Through analysis and comparison of current radiative cooling materials,polymer materials have the characteristics of high scalability,simple preparation methods,and good infrared radiation performance,and can be applied to the surface of buildings on a large scale.However,the polymer material itself has a low solar reflectance,and it relies on a highly reflective metal substrate to reflect enough sunlight.Therefore,this article selects micro-nano particles with high refractive index as the filler of the polymer.High refractive index means higher solar reflectance.Combining the properties of the two materials,a composite coating with excellent cooling performance under direct sunlight is obtained.The specific research content is as follows:(1)Using PVDF-HFP(polyvinylidene fluoride-hexafluoropropylene)as the polymer matrix,acetone as the solvent,and water as the non-solvent,the polymer porous coating is prepared by phase inversion,and the selected substrate is a highly reflective aluminum sheet.The influences of factors such as the dissolution temperature,the ratio of solvent and nonsolvent,and the thickness of the film on the solar reflectance and infrared hemispheric emissivity are explored,and the mechanism is explained by characterization methods such as SEM and FTIR.Test the outdoor cooling capacity of the coating in winter and calculate the cooling power.The results show that the optimal conditions for the synthesis of polymer porous membranes are: polymer,acetone,and water mass ratio of 1:9:1,stirring time of 2 h,dissolution temperature of 60 ℃,and thickness of 260 μm.The average reflectivity of the coated sunlight area is 95.9%,and the average emissivity of the atmospheric window is97.9%.The best radiative cooling effect that can be obtained under direct sunlight in winter is: during the day,when the solar radiation reaches the highest period,about 11:00-14:00,the temperature of the coating is 6.56 ℃ lower than the ambient temperature on average,and the maximum can be 7.3 ℃ lower.(2)Study the coatings of Zr O2,Al2O3,Ti O2 micro-nano particles and polymers for radiative cooling.The selected substrate is PMMA.SEM and XRD structural characterization and basic spectral reflectance tests were carried out on these kinds of particles.The influence of the added mass fraction of Al2O3 and the thickness of the Al2O3/PVDF-HFP composite coating on the optical properties was studied,and the optimal values of these parameters were obtained.And the applicability of the substrate and the color radiator was studied.The following conclusions are drawn: when the thickness of the composite coating is 630 μm and the content of Al2O3 powder is 50%,the optical performance of the composite coating is the best.The average reflectivity of the sunlight area is 95.3%,and the average emissivity of the atmospheric window is 96.5%.The best radiative cooling effect that can be obtained under direct sunlight in winter is: during the day,when the solar radiation reaches the highest period,about 11:00-14:00,the temperature of the coating is 6.89 ℃ lower than the ambient temperature on average,and the maximum can be 7.5 ℃ lower.In the summer test,during the day when the solar radiation reaches the highest period,about 10:00-14:00,the temperature of the coating is 11.66 ℃ lower than the ambient temperature on average,and the highest can be 13.2 ℃ lower. |
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