Fibres and cables derived from the invention might one day be used 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.
The scientists constructed the fibres by wrapping lighter-than-air, electrically conductive sheets of carbon nanotubes to form a sheath around a rubber core.
When conventional fibres are stretched, the resulting increase in length and decrease in cross-sectional area restricts the flow of electrons through the material. But the scientists claim that stretching the conducting sheath-core fibres causes little change in their electrical resistance.
One key to the performance of these conducting elastic fibres is the introduction of buckling into the carbon nanotube sheets. Because the rubber core is stretched along its length as the sheets are being wrapped around it, when the wrapped rubber relaxes, the carbon nanofibres form a complex buckled structure, which allows for repeated stretching of the fibre.
"We make the inelastic carbon nanotube sheaths of our sheath-core fibres super stretchable by modulating large buckles with small buckles, so that the elongation of both buckle types can contribute to elasticity," Dr Ray Baughman, director of the Alan G. MacDermid Nanotech Institute at UT Dallas, said. "These amazing fibres maintain the same electrical resistance, even when stretched by giant amounts, because electrons can travel over such a hierarchically buckled sheath as easily as they can traverse a straight sheath."
By adding a thin overcoat of rubber to the sheath-core fibres and then another carbon nanotube sheath, the researchers made strain sensors and artificial muscles in which the buckled nanotube sheaths act as electrodes and the thin rubber layer is a dielectric, resulting in a fibre capacitor. These fibre capacitors exhibited a capacitance change of 860% when the fibre was stretched 950%.
"This technology could be well-suited for rapid commercialisation, the rubber cores used for these sheath-core fibres are inexpensive and readily available," said Dr. Raquel Ovalle-Robles, co-author of the paper published in the journal, Science. "The only exotic component is the carbon nanotube aerogel sheet used for the fibre sheath."
