Preparation And Radiative Cooling Properties Of Polymer/Inorganic Particle Composite Fibrous Film

Daytime radiative cooling materials reflect sunlight to avoid being heated by solar irradiation,and dissipate heat to the cold outer space at the same time to realize cooling.Radiative cooling does not consume any energy,and therefore has attracted extensive attention due to its potential application prospects in many fields.In recent years,daytime radiative cooling with sub-ambient temperatures has been realized by elaborately designed photonic crystals and metamaterials.However,these materials and structures have the drawbacks of complex shape,inflexibility,high-cost,and difficulty in scaled production.They also have difficulty in being applied to buildings,vehicles and other objects that have complex surface.Herein,a flexible composite film that can be produced on a large scale was prepared by electrospinning for daytime radiative cooling.This thesis focuses on the structure and properties of the composite film:1.Composite films were prepared by electrospinning with polyvinylidene fluoride/alumina(PVDF/Al₂O₃)as raw materials.The composite films consist of ultrafine fibers of 0.5-2.5?m(diameter)with tremendous pores in between.The composite films have a high average solar reflectivity(0.97)due to the scattering of sunlight by the fibers and pores.The composite films also have a high average atmospheric window emissivity(0.95)due to the vibration of PVDF molecules and the phonon polarization resonance of Al₂O₃ nanoparticles.The results of the testing on the radiative cooling properties show that a temperature drop of 4.0?and a net radiative cooling power of 82.7 W·m^-2 can be achieved under direct sunlight.The composite films show significant radiative cooling performance in sunny,cloudy,overcast,rainy and other weather conditions.The composite films can also reduce the melting rate of ice by three times and the temperature of toy cars by 8.3?.2.Composite films were prepared by electrospinning with poly(4-methyl-1-pentene)/bismuth titanate(TPX/Bi₄Ti₃O₁₂)as raw materials.The composite films have high average solar reflectivity(0.95)and high average atmospheric window emissivity(0.91).The high solar reflectivity comes from the scattering of sunlight by composite fibers and bismuth titanate particles.The high atmospheric window emissivity results from the stretching vibration of C-C bond in poly(4-methyl-1-pentene)and Ti-O bond in bismuth titanate.Under direct sunlight,the composite films enable a temperature drop of 4.5?and an average net cooling power of 76 W·m^-2.This flexible and lightweight composite films can be prepared in large scale and at low cost.The amount of water collected by one square meter of composite films in a day(24 h)is 9.8 L,which can meet the daily drinking water volume of 8 people at the same time(one person needs about 1.2 L).The composite films can also reduce the temperature of water by 4.2?and the temperature of toy cars by 11.7?.3.Composite films were prepared by electrospinning with polyurethane/silica(PU/Si O₂)as raw materials.The films consist of ultrafine fibers of 0.1-1.1?m(diameter)with tremendous pores in between.Due to the scattering of sunlight by fibers and Si O₂particles,the composite films have a high average solar reflectivity(0.96).The composite films also have a high average atmospheric window emissivity(0.96)due to the strong absorption in the band of 8-13?m by the C-H bond,C-O bond,C=C bond in Pu and Si-O bond in Si O₂.Under direct sunlight,the temperature of the composite films can be reduced by 5.3?.The average net radiative cooling power is 67.6 W·m^-2.The composite films can also reduce the melting rate of ice by three times and the temperature of toy cars by 7.2?.