Flex material may lead to cooling clothes

A film made of tiny carbon nanotubes may be key to developing cooling clothing that can also warm you up on demand.

The carbon nanotube (CNT) film has a combination of thermal, electrical, and physical properties that make it an appealing candidate for next-generation smart fabrics, the researchers report.

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

Moreover, they achieved these properties using processes that were relatively simple and did not need excessively high temperatures.

The carbon nanotube film twists into a filament yarn and wound around a tube to show its flexibility. (Credit: Kony Chatterjee)

“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,” says co-corresponding author Tushar Ghosh, professor of textiles in North Carolina State University’s Wilson College of Textiles.

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

Cooling clothing

“Think of it like a film, with cooling properties on one side of it and heating on the other.”

“We want to integrate this material into the fabric itself,” says first author Kony Chatterjee, a PhD student. “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, Chatterjee says, 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 says.

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.

The researchers worked with with the lab of co-corresponding author Jun Liu, an assistant professor of mechanical and aerospace engineering, to accurately measure the material’s thermal conductivity. The researchers used a special experimental design to more accurately measure the material’s thermal conductivity in the direction that the electric current is moving within the material.

“If we could get the thermostat down a degree or two, that could save a tremendous amount of energy.”

“You have to measure each property in the same direction to give you a reasonable estimate of the material’s capabilities,” says Liu. “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. Researchers say that they could take advantage of this for heating, cooling, or to power small electronics.

Simple solution

Liu says 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,” Liu says. “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. They believe that a smart garment could help reduce energy consumption.

“Instead of heating or cooling a whole dwelling or space, you would heat or cool the personal space around the body,” Ghosh says. “If we could get the thermostat down a degree or two, that could save a tremendous amount of energy.”

The paper appears in the journal ACS Applied Energy Materials. The National Science Foundation and the NC State Chancellor’s Innovation Fund supported the research.

Source: NC State

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