clothing close up

Carbon nanotube clothing heats or cools on demand

Image credit: Dreamstime

Clothing that can heat or cool the wearer on demand could become reality thanks to a newly developed film made of tiny carbon nanotubes (CNT).

Researchers from North Carolina State University said the CNT film has a combination of thermal, electrical and physical properties that make it an appealing candidate for next-generation smart fabrics.

They were also able to optimise the thermal and electrical properties of the material, allowing it to retain its desirable properties even when exposed to air for many weeks.

“Many researchers are trying to develop a material that is non-toxic and inexpensive, but at the same time is efficient at heating and cooling,” said Tushar Ghosh, co-corresponding author of the study.

“Carbon nanotubes, if used appropriately, are safe and we are using a form that happens to be inexpensive, relatively speaking. It’s potentially a more affordable thermoelectric material that could be used next to the skin.”

Kony Chatterjee, first author of the study, said the team plans to integrate the material into the fabric itself: “Right now, the research into clothing that can regulate temperature focuses heavily on integrating rigid materials into fabrics, and commercial wearable thermoelectric devices on the market aren’t flexible either.”

To cool the wearer, CNTs have properties that would allow heat to be drawn away from the body when an external source of current is applied. “Think of it like a film, with cooling properties on one side of it and heating on the other,” Ghosh said.

The researchers measured the material’s ability to conduct electricity, as well as its thermal conductivity, or how easily heat passes through the material.

One of the biggest findings was that the material has relatively low thermal conductivity, meaning heat would not travel back to the wearer easily after leaving the body in order to cool it. That also means that if the material were used to warm the wearer, the heat would travel with a current toward the body and not pass back out to the atmosphere.

“You have to measure each property in the same direction to give you a reasonable estimate of the material’s capabilities,” said Jun Liu, another author on the study. “This was not an easy task. It was very challenging, but we developed a method to measure this, especially for thin flexible films.”

The research team also measured the ability of the material to generate electricity using a difference in temperature, or thermal gradient, between two environments. They said this could be used for heating, cooling or to power small electronics.

Liu said that while these thermoelectric properties were important, it was also key that they found a material that was also flexible, stable in air and relatively simple to make.

“The point of this paper isn’t that we achieved the best thermoelectric performance,” he said. “We achieved something that can be used as a flexible, electronic, soft material that’s easy to fabricate. It’s easy to prepare this material and easy to achieve these properties.”

Ultimately, their vision for the project is to design a smart fabric that can heat and cool the wearer, along with energy harvesting.

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