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Innovations in fabric technology have produced high-tech thermal properties that keep the wearer cool or warm, but a fabric that can do both has been elusive. According to information released by the University of Maryland (UMD), researchers there have created a fabric that can automatically regulate the amount of heat that passes through it, depending on conditions.
For example, when conditions are warm and moist, such as those of a sweating body on a summer day, the fabric allows infrared radiation (radiant heat) to pass through. When conditions become cooler and drier, the fabric reduces the heat that escapes. Infrared radiation is a primary way the body releases heat, and it is the focus of this new technology.
“This is the first technology that allows us to dynamically gate [regulate] infrared radiation,” said YuHuang Wang, UMD professor of chemistry and biochemistry and one of the paper’s corresponding authors.
The researchers created the fabric from specially engineered yarn coated with a conductive metal. Under hot, humid conditions, the strands of yarn compact and activate the coating, which changes the way the fabric interacts with infrared radiation to allows more heat. They refer to the action as “gating” of infrared radiation, which acts as a tunable blind to transmit or block heat.
The base yarn for this new textile is created with fibers made of two different synthetic materials—one absorbs water and the other repels it. The strands are coated with carbon nanotubes, a special class of lightweight, carbon-based, conductive metal. Because materials in the fibers both resist and absorb water, the fibers warp when exposed to humidity such as that surrounding a sweating body. That distortion brings the strands of yarn closer together, which does two things: it opens the pores in the fabric, producing a small cooling effect because it allows heat to escape; and, most importantly, it modifies the electromagnetic coupling between the carbon nanotubes in the coating.
“You can think of this coupling effect like the bending of a radio antenna to change the wavelength or frequency it resonates with,” Wang said. “It’s a very simplified way to think of it, but imagine bringing two antennae close together to regulate the kind of electromagnetic wave they pick up. When the fibers are brought closer together, the radiation they interact with changes. In clothing, that means the fabric interacts with the heat radiating from the human body.”
Depending on the tuning, the fabric either blocks infrared radiation or allows it to pass through. The reaction is almost instant, so before people realize they’re getting hot, the garment could already be cooling them down. As a body cools down, the dynamic gating mechanism works in reverse to trap in heat.
“The human body is a perfect radiator. It gives off heat quickly,” said Min Ouyang, a professor of physics at UMD and the paper’s other corresponding author. “For all of history, the only way to regulate the radiator has been to take clothes off or put clothes on. But this fabric is a true bidirectional regulator.”
More work is needed before the fabric can be commercialized, but according to the researchers, materials used for the base fiber are readily available and the carbon coating can be easily added during a standard dying process.
The paper, “Dynamic gating of infrared radiation in a textile,” Xu A. Zhang, Shangjie Yu, Beibei Xu, Min Li, Zhiwei Peng, Yongxin Wang, Shunliu Deng, Xiaojian Wu, Zupeng Wu, Min Ouyang, YuHuang Wang, was published in the February 8, 2019 edition of the journal Science.
This work was supported by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, as part of its “Delivering Efficient Local Thermal Amenities (DELTA)” program (Award No. DE-AR0000527).