Super‐Large‐Scale Hierarchically Porous Films Based on Self‐Assembled Eye‐Like Air Pores for High‐Performance Daytime Radiative Cooling

Journal Article · Thu Nov 03 00:00:00 EDT 2022 · Small

DOI:https://doi.org/10.1002/smll.202205091· OSTI ID:1896952

Tian, Qing ^[1]; Tu, Xitao ^[1]; Yang, Liu  ^[2]; Liu, Haibo ^[3]; Zhou, Yubo ^[3]; Xing, Yuxin ^[4]; Chen, Zhe ^[3]; Fan, Shanhui ^[5]; Evans, Julian ^[1]; He, Sailing ^[6]

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1. Centre for Optical and Electromagnetic Research National Engineering Research Center for Optical Instruments College of Optical Science and Engineering Zhejiang University Hangzhou 310058 China
2. Centre for Optical and Electromagnetic Research National Engineering Research Center for Optical Instruments College of Optical Science and Engineering Zhejiang University Hangzhou 310058 China, Ningbo Research Institute Zhejiang University Ningbo 315100 China
3. Ningbo Solartron Technology Co., Ltd Ningbo 315034 China
4. Centre for Optical and Electromagnetic Research National Engineering Research Center for Optical Instruments College of Optical Science and Engineering Zhejiang University Hangzhou 310058 China, Shanghai Institute for Advanced Study Zhejiang University Shanghai 200135 China
5. E. L. Ginzton Laboratory and Department of Electrical Engineering Stanford University Stanford CA 94305 USA
6. Centre for Optical and Electromagnetic Research National Engineering Research Center for Optical Instruments College of Optical Science and Engineering Zhejiang University Hangzhou 310058 China, Ningbo Research Institute Zhejiang University Ningbo 315100 China, JORCEP School of Electrical Engineering Royal Institute of Technology (KTH) Stockholm S‐100 44 Sweden

Abstract Metal‐free polymer daytime radiative cooling coatings with hierarchical eye‐like air pores are proposed and fabricated with a super‐large‐scale film‐stretching method. The hierarchically porous film (HPF) can be further coated with polymethyl methacrylate (PMMA) micro‐hemispheres, forming coated HPF (cHPF), which do not dramatically change the optical or thermal properties. The cHPF is slightly better with a lower solar absorptivity (2.4%) and a higher thermal emissivity over the atmospheric transparency window (90.1%). The low solar absorptivity is due to the strong scattering of the hierarchical eye‐like air pores, while the molecular vibrations and the focusing effect of the PMMA micro‐hemispheres contribute to the high emissivity. An average mid‐day temperature reduction of 7.92 °C is achieved relative to the air temperature, and the average cooling power reaches 116.0 W m ⁻² , which are much better than the cooling performances of the commercial cooling cushion. During the day, the cHPF‐covered simulated building is up to 6.47 and 4.84 °C cooler than the ambient and the white painted counterpart, respectively. The film is durable and resistant to chemical etching, and very promising to use globally, especially in warm and tropical regions.

• Sponsoring Organization: USDOE
• Grant/Contract Number: DE‐FG02‐07ER46426
• OSTI ID: 1896952
• Journal Information: Small, Journal Name: Small Vol. 18 Journal Issue: 51; ISSN 1613-6810
• Publisher: Wiley Blackwell (John Wiley & Sons)
• Country of Publication: Germany
• Language: English