Preparation Of Polymer/Dielectric Particle Composite Film Materials And Radiative Cooling Performance Research

Radiative cooling is a refrigeration technology that relies on thermal radiation to transfer the heat of the object itself to outer space in the form of electromagnetic waves without consuming any additional energy.It can strongly reflect the solar irradiance（0.3-2.5μm）and dissipate terrestrial heat to outer space（3 K）through the atmospheric transparency window（8-13μm）.After some groundbreaking research,the good infrared radiative performance of polymer materials shows a broad prospect in improving the passive radiative cooling performance.However,the reflectivity of the polymer itself in the solar radiative band is low,and it depends on doping inorganic dielectric particles with spectral selectivity to reflect enough sunlight,but the spectral characteristics of inorganic dielectric particles remain elusive.Therefore,this thesis selects three typical dielectric particles as the filler of polymer,calculates the optical constant and corresponding radiation characteristics of dielectric particles through the first principle and Mie scattering theory,discusses the internal relationship between the optical constant and spectral characteristics,and combines the properties of the three dielectric particles to obtain a composite material with excellent radiative cooling performance under daytime illumination.The main contents are as follows:1.Hierarchically porous composite film was prepared by phase separation method with silica（SiO₂）and polyvinylidene fluoride co-hexafluoropropylene（P（Vd F-HFP））as raw material.There are a large number of randomly distributed holes and silica particles in the composite film material.the composite film material has a high solar reflectivity（96.25%）due to the scattering of sunlight by holes and silica.In addition,the composite film has excellent atmospheric window emissivity（95.40%）based upon the interaction of the functional group vibration of P（Vd F-HFP）and the infrared phonon of silica.The results of the outdoor cooling effect testing shows that under the conditions of solar irradiance of 527.6 W/m²,wind speed irradiance of 1.08 km/h,and air humidity of 15.8%,the average temperature drop（?T）is5.94℃.The composite film material still shows excellent flexibility and mechanical properties while ensuring excellent radiative cooling performance.At the same time,due to the excellent hydrophobic performance of the material,the influence of outdoor pollutants on the cooling performance of the material is avoided.2.Hierarchically porous composite film was prepared by phase separation method with barium sulfate（BaSO₄）and polyvinylidene fluoride co-hexafluoropropylene（P（Vd F-HFP））as raw material.The porous composite film material has high solar reflectivity（97.90%）and high atmospheric window emissivity（96.56%）.The hierarchical porous structure combined with the appropriate optical constant of barium sulfate promotes the multiple scattering of sunlight,the high emissivity of the material comes from the vibration of C-H and C-F bonds of the polymer and the infrared photo-phonon mode of barium sulfate particles.Under direct sunlight,the composite films realized a sub-ambient temperature drop of 10.09℃.Moreover,it has excellent sub-environment radiative cooling effect in sunny,cloudy,overcast,and other weather conditions.The composite film material also has excellent flexibility and mechanical propertie,and exhibits some self-cleaning ability,which helps the material to be used in practical environments.3.Hierarchically porous composite film was prepared by phase separation method with alumina（Al₂O₃）and polyvinylidene fluoride co-hexafluoropropene（P（Vd F-HFP））as raw material.The composite film surface presents a hierarchical texture with the micro-pleats,and the interior is a hierarchical porous morphology,in which the alumina particles are distributed in a random disordered state.Due to the scattering of alumina particles and hierarchical porous structure,the composite films have a large solar reflectivity（～98.15%）.In addition,the polymer has multiple extinction absorption peaks caused by different functional group vibration modes in the thermal wavelengths,combined with the rich harmonic phonon dispersion of alumina,resulting in a highly atmospheric window emissivity（97.56%）.Under direct sunlight in summer,the maximum temperature difference can reach 12.6°C,and the average temperature drop is9.1°C.Herein,we applied the material to prevent ice melting,and the material can reduce the ice melting rate by four times.In the adaptability test,the material shows excellent flexibility,mechanical properties,and self-cleaning performance.