目的 针对现有辐射制冷材料形态单一、双波段光学协同性不足的瓶颈,提出双波段协同优化策略并且研制形态可调控的辐射制冷材料。方法 将太阳光波段和红外波段耦合,分析不同功能成分的特点,通过添加金属氧化物,降低了辐射制冷材料对于基底高反射性的要求,并且综合提高材料的制冷性能;通过调控PDMS含量,实现涂层或薄膜的材料形态的灵活转换。采用紫外-可见-近红外光谱仪、傅里叶红外光谱仪分别测试涂层和薄膜的光谱,将涂层和薄膜覆盖在金属板上测试实际的降温效果。结果 光谱性能上,Al2O3浓度优化至40%时太阳光反射率提升至0.93,理论制冷功率增益达22%。使用制备的辐射制冷涂层和薄膜进行了辐射制冷实验,在>36 ℃高温环境下添加Al2O3的涂层样品实现了平均2.9 ℃、峰值5.1 ℃的温降;薄膜可实现平均1.9 ℃的降温效果。材料形态上,当PDMS与丙酮的质量比大于等于1∶5时,涂料能牢固附着于基底表面形成涂层;当质量比为1∶6时,涂料与基底之间吸附力较弱,干燥后可完整地脱落形成自支撑薄膜。结论 通过调整太阳光散射体和红外发射聚合物基体对材料进行形态和双波段光谱优化,该材料以低成本、高效率和形态可控优势,为辐射制冷技术规模化应用提供了切实可行的解决方案。
Abstract
Passive daytime radiative cooling (PDRC) radiates heat into the ultracold universe and reflects sunlight simultaneously, offering significant potential for sustainable thermal management, renewable power generation, atmospheric water harvesting, and agricultural preservation. However, current radiative cooling materials cannot achieve multiple forms with the same formula. This results in considerable difficulties during retrofitting or removal operations, and substantially increased construction costs and maintenance burdens. To address this disadvantage, morphologically controllable daytime radiative cooling materials are developed. A dual-band selective spectrum regulation strategy is proposed to simultaneously optimize spectral performance of the developed materials across both solar and infrared bands through systematically characterizing the wavelength-selective properties of functional components.
Material morphology is controlled by adjusting the polydimethylsiloxane (PDMS) content in a solution of polyvinylidene fluoride (PVDF) in acetone. When PDMS-to-acetone mass ratio is 1∶5 or higher, the mixture forms a coating adhering firmly to the substrate upon drying. When the ratio is 1∶6, the adhesion is weak, and the dried paint can be peeled off as a free-standing film. The spectral properties of both coatings and free-standing films are characterized by ultraviolet-visible-near infrared (UV-Vis-NIR) spectrophotometry and Fourier transform infrared (FTIR) spectroscopy.
Metal compounds are also used to significantly reduce the reliance on the high substrate reflectivity and improve the cooling performance. Experiments on cooling performances are carried out by applying the developed coatings and free-standing films onto aluminum plates. By adding 20wt.% aluminum oxide (Al2O3) and 10wt.% polytetrafluoroethylene (PTFE) powder into PDMS-PVDF paint as solar scatters, the solar reflectivity of the coatings on aluminum substrates increases substantially from 0.614 to 0.910. Notably, the addition of PTFE powder reduces the required concentration of metallic solar scatters, thereby lowering the coating density and production costs. For comparison, barium sulfate (BaSO4), titanium dioxide (TiO2), and Alumina (Al2O3) are evaluated as solar scatters by preparing coatings and free-standing films using identical PVDF-PDMS methodologies. The solar reflectivity of the TiO2-based and Al2O3-based coatings on aluminum substrates is 0.909 and 0.910, respectively, while that of the corresponding free-standing films is 0.908 and 0.891, respectively.
The TiO2-based coating exhibits exceptional spectral independence on the underlying substrate due to the characteristically high refractive index of TiO2, enabling saturated optical scattering even at low mass fractions. Conversely, Al2O3 has a comparatively lower refractive index, resulting in incomplete spectral decoupling of the Al2O3-based coating. This is evidenced by the average solar reflectivity of the corresponding Al2O3-based free-standing film being 0.02 lower than that of the Al2O3-based coating on the aluminum plate. Therefore, a higher concentration of Al2O3 scatters is required to enhance the scattering cross section and maximize solar reflectivity. At an optimized concentration of 40wt.%, the Al2O3-based coating achieves a solar reflectivity of 0.93, corresponding to a theoretical cooling power gain of 22%, while the TiO2-based coating maintains a reflectivity of 0.911 at the same concentration. Crucially, the infrared emissivity remains virtually unaffected by the addition of these metal compounds.
Field experiments are conducted on a 40wt.% Al2O3-based coating, a 40wt.% TiO2-based coating, and a 20wt.% Al2O3-based coating/free-standing film to quantify practical cooling performance. When the ambient temperature exceeds 36 ℃, the 40wt.% Al2O3-based coating achieves the highest average temperature reduction of 2.9 ℃, and the 40wt.% TiO2-based coating achieves an average reduction of 2.3 ℃. Temperature reductions for the 20wt.% Al2O3-based coating and its corresponding free-standing film are 2.3 ℃ and 1.9 ℃, respectively.
In conclusion, through tuning solar scatters and infrared-emissive polymer matrices, this work successfully realizes both morphological control and dual-band selective spectrum regulation. The developed material system offers a feasible solution for scalable daytime radiative cooling applications, and has advantages of cost-effectiveness, high thermal performance, and controllable physical morphology adaptable to diverse implementation scenarios.
关键词
白天辐射制冷 /
涂层 /
薄膜 /
双波段优化 /
多形态 /
热辐射
Key words
daytime radiative cooling /
coating /
film /
dual-band selective spectrum regulation /
flexible morphology /
thermal radiation
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基金
国网江苏省电力有限公司科技项目（J2025077）
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