An international team of researchers from the University of Texas at Dallas and Hanyang University in South Korea have developed a type of yarn called Twistron that is made from carbon nanotubes—a type of cylindrical carbon molecules with unusual thermal, mechanical, and electrical properties—and can generate electricity when coiled or stretched.
"The researchers first twist-spun the nanotubes into high-strength, lightweight yarns," according to a press release. "To make the yarns highly elastic, they introduced so much twist that the yarns coiled like an over-twisted rubber band." To make the yarns conductive, the team then submerged them into an electrolyte bath that charged the yarn. “Fundamentally, these yarns are supercapacitors,” said Na Li, a research scientist at the Alan G. MacDiarmid NanoTech Institute of the University of Texas at Dallas, and co-author of the study in the release. “In a normal capacitor, you use energy (like from a battery) to add charges to the capacitor. But in our case ... no external battery, or voltage, is needed.”
In a conductive state, when the material is coiled or stretched, the diameter of the yarn decreases. As a result, the distance between electric charges decreases which then enhances the energy capabilities of the material. "This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity," said Carter Haines, associate research professor at the NanoTech Institute, and co-author of the study. At a twist rate of 30 times a second, the yarn can generate electrical power equal to 114 watts per pound.
Recently, the researchers have tested applicability of the yarn in the lab. They attached a LED lamp to a Twistorn yarn and observed how it lit up the lamp when it was stretched. Other possible applications of Twistron might enable harvesting energy from the oceans' wave motions or "temperature fluctuations," according to a press release.