Yarns, made of the tiny straws of carbon called nanotubes, have an astounding ability to twist as they contract, according to scientists. The effect, reported in Science, is similar to the action of muscles found in elephant trunks and squid tentacles.
A team of researchers from Australia, the U.S., Canada and South Korea demonstrated motors that could spin at nearly 600 revolutions per minute, turning a weight 2,000 times heavier than the yarn itself.
The nanotubes are spun into helical yarns. This means they have left and right handed versions, which allows the yarn to be controlled by applying an electrochemical charge and to twist and untwist.
The nanotube yarns are activated by charging them in a salt solution, in much the same way as a battery. The helical structure of the yarns makes them unwind as they accept charge and swell, twisting back up again, when discharged.
The torque that we can generate per mass of the yarn is comparable to that of very large electric motors. But as you down-size electric motors you dramatically decrease the torque capabilities per weight, and make the motors very expensive, said Professor Ray Baughman of the University of Texas at Dallas. The professor is a renowned researcher into the tubes' properties and is co-author of the new research.
The yarns were made by pulling sheets of nanotubes from forests of the tubes and twisting them to form a coiled structure - much as yarn is made from wool.
These twisted tubes were then dipped in an electrolyte - a fluid containing ions or electrically charged atoms. When voltage was applied at the ends of the yarns, these ions moved into the fibres, causing them to expand.
Often you want to control the movement of fluids, you want to pump them from one place to another or turn off one flow and open up another, and the carbon nanotube muscles because of their very small size seem very suitable for this type of application, said Prof. Baughman.