University of Texas at Dallas researchers have made electrically conducting fibers that can be reversibly stretched to over 14 times their initial length. Electrical conductivity of the fibers increases 200-fold when stretched.

The new fibers will be used to create artificial muscles, as well as capacitors. Fibers and cables derived from the invention may one day acts as interconnects for super-elastic electronic circuits; robots and exoskeletons; morphing aircraft; giant-range strain sensors; failure-free pacemaker leads; and super-stretchy charger cords for electronic devices.

To construct the fibers, the UT Dallas scientists wrapped sheets of tiny carbon nanotubes to form a sheath around a long rubber core. The rubber core is stretched along its length as the sheets are being wrapped around it. When the wrapped rubber relaxes, the carbon nanofibers form a complex buckled structure, which allows for repeated stretching of the fiber.

The fibers maintain the same electrical resistance, even when stretched. The buckling in two dimensions avoids misalignment of nanotube and rubber core directions.

By adding a thin overcoat of rubber to the sheath-core fibers and then another carbon nanotube sheath, the researchers made strain sensors and artificial muscles in which the buckled nanotube sheaths serve as electrodes; the thin rubber layer is a dielectric, resulting in a fiber capacitor. The fiber capacitors exhibited a capacitance change of 860 percent when the fiber was stretched 950 percent.

Adding twist to the double-sheath fibers resulted in fast, electrically powered torsional artificial muscles that could be employed to rotate optical-circuit mirrors or pump liquids in miniature devices used for chemical analysis.