Research On Polymer-Materials Based Radiative Cooling Films

With the continuous development of the construction industry,the amount of energy required for construction and operation is increasing,and the total energy consumption of buildings is also growing year by year,ranking the first in energy consumption of all industries.Up to now,China's building energy conservation level is far behind the developed countries.Building energy conservation has become an urgent task.On the other hand,radiative cooling,as a passive cooling method without energy input,can reduce the building temperature and realize the purpose of energy saving by covering the building surface with radiative materials.This approach has great potential in the application of building energy saving.The key to realizing effective radiative cooling lies in the selective control of the radiation characteristics of solar and mid-infrared spectra.In previous studies,most of the metamaterials that realize radiative cooling are prepared by micro-nano processing technology,which requires complex processes and high costs.They are difficult to achieve large-scale production.However,the optical material based on doping the micro-nano particles and multi-layer polymer structure have the corresponding excellent radiative properties.They have attracted more and more attention because of their simple structures and the advantages of low cost and large scale preparation.In this paper,in order to realize low cost growing preparation and excellent refrigeration effect,for the purpose of using two different design methods,finally a double-layer film composed of polyfluoroethylene(PVF)layer,the silver coating is proposed as an effective daytime radiation cooler with low solar absorption and wide-band infrared radiation characteristics,which can realize the passive energy saving of buildings.Based on the FDTD commercial software and the ray-tracing method,respectively to study the radiative characteristics of the nano radiative film with ordered doping of Si O2 microspheres in polymethlpenten(TPX)substrate and the double-layer composite film composed of four common polymer materials: polydimethylsiloxane(PDMS),polymethyl methacrylate(PMMA),polyvinyl chloride(PVC),polyvinyl fluoride(PVF).The influence of sillica(Si O2)microsphere diameter,TPX substrate thickness and polymer film thickness on the refrigeration effect was discussed,and the structure was optimized.Finally,it was determined that the radiative cooling film composed of the PVF radiative layer and metallic silver reflection layer had the best spectral characteristics and could achieve the best refrigeration effect.In this paper,the mechanical property was measured by the material tensile modulus scale.We discussed the influence of the thickness of the polymer layer on the tensile modulus of the model.After comprehensively considering the sample preparation cost,refrigeration efficiency,mechanical properties,and other factors,we determined the optimal film material and configurator: PVF radiative layer thickness was 2 mm,and metallic silver reflecting layer thickness was 200 nm.In this paper,we prepared the PVF-Ag double-layer film by the biaxial stretching process and magnetron sputtering coating process.Then we measured the optical properties and cooling effects of the film samples.The experimental results show that the PVF-Ag double-layer has excellent infrared radiation characteristics and solar spectral reflectivity.Under the solar irradiation of 950 W/m2,the cooler can still achieve a cooling effect of 2 ? lower than the ambient temperature,successfully making daytime sub-ambient cooling.We discussed the similarities and differences between the experimental results and theoretical results,analyzed the reasons theoretically,and demonstrated once again that PVF composite film could be applied to building energy conservation and have good application prospects.