Preparation and properties of polyethylene oxide/Al2O3 passive radiative cooling membrane
Objective Rapid population growth and industrialization cause global warming.Improving the cooling efficiency of materials and slowing down global warming become a top priority.With the development of micro/nano technology,through the design and preparation of new materials,high solar reflectivity and high infrared emissivity in the atmospheric window band infrared emissivity can be achieved to improve the daytime radiative cooling effect.Method Using polyethylene oxide(PEO)as the raw material,PEO fibrous membranes were prepared through electrospinning technology.PEO/A12O3 fibrous membranes were fabricated by combining different contents of nano-Al2O3 into PEO micro-nanofibers through a blending method.The morphology,reflectance of sunlight,mid-infrared transmittance and emissivity in the atmospheric window,and daytime radiative cooling performance of fibrous membranes were studied and analyzed.Results Through SEM analysis,it was confirmed that the nano-Al2O3 particles were combined into the fibers,and the diameters of the fibers obtained by electrospinning were mainly distributed in the range of 0.2-1.6 μm,while the solar spectrum was in the range of 0.25-2.5 μm,demonstrating that the fibrous membrane has a strong scattering effect on sunlight.The increase in the content of nano-Al2O3 particles in fibrous membrane was confirmed by EDS analysis.The crystallization properties of the fibrous membranes were analyzed,and the results confirmed the existence of nano-Al2O3 particles in the FPRC-4 membrane.The chemical structure analysis suggested that the FPRC-4 membrane had no obvious characteristic peak in the mid-infrared band of 8-13 μm,and that it can achieve selective emission in the wavelength range of 8-13 μm.The effects of Al2O3 content and membrane thickness on solar light reflectance and mid-infrared transmittance were studied.The results indicated that owing to the effective scattering of micro-nanofiber structure and nano-Al2O3,the average solar light reflectance of the membrane was 90.2％,and the average transmittance in the atmospheric window was 93.5％.When the Al2O3 mass fraction was 4％,the PEO/Al2O3 fibrous membrane has the best optical properties.The solar light reflectance would increase with the increase of thickness,while the change in the mid-infrared transmittance with the increase of thickness was not obvious.The influence of added Al2O3 nanoparticles on the emissivity of the fibrous membrane was studied.The results showed that the introduction of nano-Al2O3 particles increased the overall infrared emissivity of FPRC-4 membrane to 80.3％,compared to the relatively low infrared emissivity of the pure PEO membrane(56.5％),and the average emissivity of FPRC-4 membrane in the atmospheric window was as high as 90.0％.Radiative cooling experiments were conducted using a self-designed testing setup to investigate the cooling performance of the samples.With an Al2O3 mass fraction of 4％,a temperature decrease of 6.1 ℃ was achieved during daytime under an average solar irradiance of 712.3 W/m2and an average ambient humidity of 14.2％.The actual cooling effectiveness of the membrane was tested.Infrared camera observed that the surface temperature of the FPRC-4 sample was significantly lower than that of the control sample,indicating good radiative cooling performance of the FPRC-4 sample.Conclusion The radiative cooling performance is closely associated with multiple factors.The Al2O3 content and membrane thickness have an impact on the solar light reflectance,mid-infrared transmittance in the atmospheric window region,emissivity,and radiative cooling performance of the fibrous membrane.Analysis of solar light reflectance spectra and mid-infrared transmittance spectra demonstrated that with an Al2O3 mass fraction of 4％and a thickness of 0.2 mm,the fibrous membrane achieved a daytime temperature reduction of 6.1 ℃.Radiative cooling technology holds promise for assisting China in achieving peak carbon emissions and carbon neutrality.The use of such fibrous membranes for energy-efficient radiative thermal regulation provides new avenues and approaches for mitigating global warming and advancing the development of renewable energy-saving refrigeration technologies.
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