Science - Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles
Individual carbon nanotubes are stronger than steel, highly conductive, have great optical properties, and so on—you’ve heard the hype. But single nanotubes are not so useful. For many years, when researchers tried to build things out of them, they had trouble getting these properties to scale from single tubes to larger structures. One problem is the tendency for nanotubes to form spaghetti-like tangles, where each point of tube-to-tube contact can compromise strength. But over the past few years materials scientists have been learning how to straighten out these tangles and build large, useful things.
The trick in this case is a set of yarn-weaving techniques developed by Ray Baughman at the University of Texas at Dallas. His group starts by growing a vertical forest of carbon nanotubes, then dragging a roller over the top. As the tubes are pulled, they come together in a thin, stretchy sheet. The nanotubes in the sheet are all lined up like spaghetti in a box, and this alignment helps maintain their individual strength on a collective level. To make the nanotube muscles, the Texas researchers coat this sheet with a filler material that expands dramatically when heated. Then they weave the sheet into yarns with different twisting configurations. When the yarns are heated, the filler expands dramatically, and the yarn will contract in a way that’s determined by its coiling configuration.
ABSTRACT - Artificial muscles are of practical interest, but few types have been commercially exploited. Typical problems include slow response, low strain and force generation, short cycle life, use of electrolytes, and low energy efficiency. We have designed guest-filled, twist-spun carbon nanotube yarns as electrolyte-free muscles that provide fast, high-force, large-stroke torsional and tensile actuation. More than a million torsional and tensile actuation cycles are demonstrated, wherein a muscle spins a rotor at an average 11,500 revolutions/minute or delivers 3% tensile contraction at 1200 cycles/minute. Electrical, chemical, or photonic excitation of hybrid yarns changes guest dimensions and generates torsional rotation and contraction of the yarn host. Demonstrations include torsional motors, contractile muscles, and sensors that capture the energy of the sensing process to mechanically actuate.
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