COLLEGE PARK, Md. – Despite decades of innovation in fabrics with high-tech thermal properties that keep marathon runners cool or alpine hikers warm, there has never been a material that changes its insulating properties in response to the environment. Until now. 

University of Maryland researchers 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 is the focus of this new technology.

A paper on their work was just published in in the journal Science.

“This is the first technology that allows us to dynamically gate [regulate] infrared radiation,” said YuHuang Wang, a 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 that allows. 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. First, it opens the pores in the fabric. This has a small cooling effect because it allows heat to escape. Second, 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. On the flip side, 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.”

According to the Science paper, this is first textile shown to be able to regulate heat exchange with the environment.

“This pioneering work provides an exciting new switchable characteristic for comfort-adjusting clothing,” said Ray Baughman, a professor of chemistry at the University of Texas who was not involved in the study. “Textiles were known that increase porosity in response to sweat or increasing temperature, as well as textiles that transmit the infrared radiation associated with body temperatures. However, no one before had found a way to switch both the porosity and infrared transparency of a textile so as to provide increased comfort in response to environmental conditions.”

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 standard dying process.

“I think it’s very exciting to be able to apply this gating phenomenon to the development of a textile that has the ability to improve the functionality of clothing and other fabrics,” Ouyang said.

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, is 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). The content of this article does not necessarily reflect the views of this organization.

COLLEGE PARK, Md. – For all their destructive power, most volcanic eruptions are local events. Lava flows tend to reach only a few miles at most, while airborne ash and soot travel a little further. But occasionally, larger eruptions can launch particles into the stratosphere, more than 6 miles above Earth’s surface. The 1991 eruption of Mount Pinatubo in the Philippines—the world’s largest eruption in the past 100 years—is a prime example of a stratospheric eruption.

When volcanic particles reach the stratosphere they stay aloft for a long time, reflecting sunlight and temporarily cooling the planet. By understanding the history of these big eruptions, researchers can begin to place short cooling episodes and other discrete climate events into the context of large-scale climate patterns.

Researchers working at the University of Maryland, the Université Grenoble Alpes in France, the Ecole Normale Supérieure in France and the Tokyo Institute of Technology have devised a new, more accurate system for identifying large stratospheric eruptions recorded in the layers of Antarctic ice cores.

Using their method, the researchers have made some important revisions to the known history of big eruptions—correcting the record on several misidentified events while discovering a few as-yet unknown stratospheric eruptions. The researchers described their approach, which identifies volcanically-sourced sulfate molecules with a specific chemical signature, in a paper published January 28, 2019, in the journal Nature Communications.

“I find it very exciting that we are able to use chemical signals to build a highly accurate record of large, climate-relevant, stratospheric eruptions,” said James Farquhar, a professor of geology at UMD and a co-author of the research paper. “This historical record will be highly useful for climate scientists seeking to understand the role of large eruptions in climate oscillations. But there is also the basic marvel of reading a chemical fingerprint that is left behind in ice.”

Eventually, volcanic particles do fall from the stratosphere, settling on the ground below. When they land on snow, the particles are soon covered by more snow that gets compacted into ice. This preserves a record of the eruption that survives until the ice melts. Researchers can drill and retrieve ice cores in places like Antarctica and Greenland, revealing eruption records that can stretch back several thousand years.

Because particles from large stratospheric eruptions can spread across the globe before falling to the ground, previous methods to identified stratospheric eruptions by looking for sulfate particle layers in ice from both hemispheres—usually from Antarctica and Greenland. If the same layers of sulfate showed up in both cores, deposited at the same time in Earth’s history, researchers would conclude that the particles came from the same large, stratospheric eruption.

“But for eruptions that are intense enough to inject material into the stratosphere, there is a telltale signature in the sulfur isotope ratios of sulfate preserved in ancient ice layers,” explained Farquhar, who also has an appointment at UMD’s Earth System Science Interdisciplinary Center. “By instead focusing on this distinct sulfur isotope signature, our new method yielded some surprising and useful results. We found that prior reconstructions missed some stratospheric events and falsely identified others.”

Lead author of the study Elsa Gautier, of the Université Grenoble Alpes, did a significant portion of the analyses at UMD while on a Fulbright Fellowship to work with Farquhar in 2013. Following Gautier’s lead, the researchers developed their method using ice cores collected at a remote site in Antarctica called Dome C. One of the highest points on the Antarctic ice sheet, Dome C is home to ice layers that stretch back nearly 50,000 years.

Gautier and her colleague Joel Savarino, also at Université Grenoble Alpes, collected ice cores at Dome C that contain records stretching back roughly 2600 years, covering a large portion of recorded human history.

The researchers used their method to confirm that many events had indeed been properly identified by the older method of matching up corresponding sulfate layers in ice cores from both hemispheres. But some events, formerly thought to be big stratospheric eruptions, did not have the telltale sulfur isotope signature in their sulfate layers. Instead, the researchers concluded, these layers must have been deposited by two or more smaller volcanoes that erupted at about the same time at high latitudes in both hemispheres. 

The researchers also found some big stratospheric events that do contain the isotope signature, but were somehow constrained to the Southern Hemisphere.

“This is a strength of our approach, because these events would have a climate impact but are missed by other methods,” Farquhar said. “We have made a significant improvement to the reconstruction of large stratospheric eruptions that occurred over the past 2600 years. This is critically important for understanding the role of volcanic eruptions on climate and possibly for understanding certain events in human history, such as widespread famines. It can also help to inform future climate models that will take large volcanic events into account.”

The research paper, “2600 years of stratospheric volcanism through sulfate isotopes,” Elsa Gautier, Joel Savarino, J. Hoek, J. Erbland, N. Caillon, S. Hattori, N. Yoshida, E. Albalat, F. Albarede and James Farquhar, was published in the journal Nature Communications on January 28, 2019.

This work was supported by the Institut National des Sciences de l’Univers, the Agence Nationale de la Recherche (Award No. NT09-431976-VOLSOL), Labex OSUG@2020 (Award No. ANR10LABX56), the Institute Polaire Paul-Emile Victor (Award No. SUNITEDC No. 1011), and the Japan Society for the Promotion of Science (Award Nos. 25887025, 16H05884 and 17H06105). The content of this article does not necessarily reflect the views of these organizations.