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Glass-hybrid plastic offers passive cooling

Low-cost silica-doped polymer excels at daytime radiative cooling by strongly emitting IR light and not absorbing much sunlight

by Mitch Jacoby
February 13, 2017 | A version of this story appeared in Volume 95, Issue 7

If the temperature of buildings could be controlled by simply covering them with a plastic wrap that dissipates daytime heat without consuming electricity, owners could save a bundle on energy costs. Researchers at the University of Colorado, Boulder, have taken a key step in that direction by developing an inexpensive glass-polymer hybrid material that excels in this type of passive cooling (Science 2017, DOI: 10.1126/science.aai7899). Scientists have identified a number of materials for efficient nighttime radiative cooling. But daytime cooling remains a challenge because solar absorbance of just a few percent exceeds many materials’ cooling capacities, causing buildings and other surfaces to become hot. So Colorado mechanical engineers Ronggui Yang, Xiaobo Yin, and coworkers devised a material that strongly emits thermal energy in the form of infrared light and hardly absorbs sunlight. The material, which the team makes via low-cost roll-to-roll manufacturing methods, consists of randomly distributed micrometer-sized SiO2 spheres embedded in a poly(methylpentene) matrix. A 50-μm-thick film of the transparent material containing 6% microspheres by volume emits intensely throughout the IR region and reflects approximately 96% of solar radiation when backed with a 200-nm-thick silver coating. Having conducted initial lab tests, the team now plans to evaluate the technology this summer in the form of a 20 m2 roof cover on Colorado’s engineering building.

This image depicts the composition of a glass-embedded polymer and a photo of a large film of the material.
Credit: Science
Produced via roll-to-roll manufacturing, this low-cost film made of silica spheres embedded in a polymer matrix efficiently cools sunlit surfaces.
This image depicts the composition of a glass-embedded polymer and a photo of a large film of the material.
Credit: Science


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