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Abstract Many materials have been explored for the purpose of creating structures with high radiative cooling potential, such as nanocellulose-based structures and nanoparticle-based coatings, which have been reported with environmentally friendly attributes and high solar reflectance in current literature. They each have their own advantages and disadvantages in practice. It is worth noting that nanocellulose-based structures have an absorption peak in the UV wavelengths, which results in a lower total solar reflectance and, consequently, reduce radiative cooling capabilities. However, the interwoven-fiber structure of cellulose gives high mechanical strength, which promotes its application in different scenarios. The application of nanoplatelet-based coatings is limited due to the need for high volume of nanoparticles to reach their signature high solar reflectance. This requirement weakens the polymer matrix and results in more brittle structures. This work proposes a dual-layer system, comprising of a cellulose-based substrate as the bottom layer and a thin nanoparticle-based radiative cooling paint as the top layer, where both radiative cooling potential and mechanical strength can be maximized. Experimental and theoretical studies are conducted to investigate the relationship between thickness and reflectance in the top coating layer with a consistent thickness of the bottom layer. The saturation point is identified in this relationship and used to determine the optimal thickness for the top-layer to maximize material use efficiency. With the use of cotton paper painted with a 125 μm BaSO4-based layer, the cooling performance is enhanced to be 149.6 W/m2achieved by the improved total solar reflectance from 80 % to 93 %.
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Scalable Aqueous Processing‐Based Passive Daytime Radiative Cooling Coatings
Abstract Passive daytime radiative cooling (PDRC) can realize electricity‐free cooling by reflecting sunlight and emitting heat to the cold space. Current PDRC designs often involve costly vacuum processing or a large quantity of harmful organic solvents. Aqueous and paint‐like processing is cost‐effective and environmentally benign, thereby highly attractive for green manufacturing of PDRC coatings. However, common polymers explored in PDRC are difficult to disperse in water, let alone forming porous structures for efficient cooling. Here, a simple “bottom‐up” ball milling approach to create uniform microassembly of poly(vinylidene fluoride‐co‐hexafluoropropene) nanoparticles is reported. The micro‐ and nanopores among secondary particles and primary particles substantially enhance light scattering and results in excellent PDRC performance. A high solar reflectance of 0.94 and high emittance of 0.97 are achieved, making the coating 3.3 and 1.7 °C cooler than commercial white paints and the ambient temperature, under a high solar flux of ≈1100 W m−2. More importantly, the volatile organic compound content in the aqueous paint is only 71 g L−1. This satisfies the general regulatory requirements, which are critical to sustainability and practical applications.
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- Award ID(s):
- 2005747
- PAR ID:
- 10452974
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 31
- Issue:
- 19
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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