Researchers have created energy-harvesting yarn from tightly coiled carbon nanotubes, which can be activated by the electrolytes in a simple saline solution. With no need for a battery, these “twistron yarns” have numerous potential applications in wearable, medicinal and oceanic contexts.
How twistron yarn is made
An international research team led by scientists at The University of Texas at Dallas (UT Dallas) and Hanyang University in South Korea constructed the yarn from carbon nanotubes—hollow cylinders 10,000 times smaller in diameter than a human hair. After twist-spinning sheets of carbon nanotubes—with a motion similar to a spinning wheel—to create strong, lightweight yarns, researchers introduced elasticity with additional twist until the yarns coiled akin to an over-twisted rubber band.
“We just have little electric motors, and we turn on the power and it spins. And we can attach that sheet to the motor, and it spins into yarn—just like you’re making sheep’s wool,” according to lead author Carter Haines, a nanotech researcher at the UT Dallas. “The one additional trick is we twist the yarn to a very high degree until it starts to coil on itself. Under the right conditions, you’ll get a nice coil like a spring, and if you get the spring, you have the stimulus you need to create electricity.”
Haines further simplified the scientific process, saying: “The easiest way to think of twistron harvesters is, you have a piece of yarn, you stretch it, and out comes electricity.”
Haines explained that during the twisting process, the volume of the yarn decreases, which brings the electric charges closer—thereby increasing their energy. This allows for the harvesting of electricity, by increasing the voltage coupled with the charge stored in the yarn. The study showed a twistron yarn that weighs less than a fly can light a small LED.
The yarn requires an electrolyte wash for its power source, such as a simple mixture of table salt and water, which will render the ions conductive.
Dr. Na Li, a research scientist at the NanoTech Institute and co-lead author of the study said, “Fundamentally, these yarns are supercapacitors.” Li added, “In a normal capacitor, you use energy—like from a battery—to add charges to the capacitor. But in our case, when you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself. No external battery, or voltage, is needed.”
The UT Dallas study reports that the carbon nanotubes yarn produces more power than any other energy-harvesting device ever developed. Another co-author, Dr. Ray Baughman, director of the NanoTech Institute, explained that stretching coiled twistron 30 times per second created 250 watts per kilogram of peak electrical power, after being normalized for the harvester’s weight.
Baughman said, “Although numerous alternative harvesters have been investigated for many decades, no other reported harvester provides such high electrical power or energy output per cycle as ours for stretching rates between a few cycles per second and 600 cycles per second.”
In short, according to Baughman, “There’s basically no game in town which gives comparable power output to our yarns.”
Potential uses for twistron technology
Despite researchers’ pride in their newfound nanotube power source, energy-harvesters aren’t powering large items such as automobiles and houses. Instead, they are ideal for technology when changing batteries is impractical, according to Yu Jia from the University of Chester in the UK. For instance, previous versions of energy harvesters have powered sensors under a bridge and underneath trains for maintenance and testing purposes. The jostling of the trains on the tracks or cars on the bridge stretched the energy-harvesters to create electricity.
With the latest yarn triggered by electrolytes, researchers were encouraged to apply the technology to wearables—sewing twistron into workout clothing that would be activated by movement and perspiration.
To read more, please continue to page 2.