It wasn’t all that long ago that an exotic new material, carbon nanotubes, caught a lot of imaginations with endless possibilities, including supporting and conveying an elevator from earth to space. Those dreamy beginnings for carbon nanotubes never quite seemed to materialize. However, things are changing and carbon nanotubes again seem to be gathering some momentum as a reality in our lives.
A huge leap forward in nanotechnology was recently announced by Rice University. Scientists from Rice, the Dutch firm Teijin Aramid, the U.S. Air Force, and Israel’s Technion Institute recently unveiled a new carbon nanotube (CNT) fiber that looks and acts like textile thread and conducts electricity and heat like a metal wire. The researchers say they have come up with an industrially scalable process for making the threadlike fibers, which outperform commercially available high-performance materials.
“We finally have a nanotube fiber with properties that don’t exist in any other material,” said lead researcher Matteo Pasquali, professor of chemical and biomolecular engineering and chemistry at Rice. “It looks like black cotton thread but behaves like both metal wires and strong carbon fibers.”
“The new CNT fibers have a thermal conductivity approaching that of the best graphite fibers but with 10 times greater electrical conductivity,” said study co-author Marcin Otto, business development manager at Teijin Aramid. “Graphite fibers are also brittle, while the new CNT fibers are as flexible and tough as a textile thread. We expect this combination of properties will lead to new products with unique capabilities for the aerospace, automotive, medical, and ‘smart-clothing’ markets.”
The phenomenal properties of carbon nanotubes have fascinated scientists since their discovery in 1991. The hollow tubes of pure carbon, which are aboutas wide as a strand of DNA, are about 100 times stronger than steel at one-sixth the weight. Nanotubes’ conductive properties — for both electricity and heat — rival the best metal conductors. They also can serve as light-activated semiconductors, drug-delivery devices, and even sponges to soak up liquids.
Carbon nanotubes, despite their huge potential, are difficult to work with. For starters, finding a method for producing bulk quantities of nanotubes took a decade. Scientists also learned early on that there were several dozen types of nanotubes — each with unique material and electrical properties; and engineers have yet to find a way to produce just one type. Instead, all production methods yield a hodgepodge of types, often in hairball-like clumps.
Shortly after arriving at Rice in 2000, Pasquali began studying CNT wet-spinning methods with the late Richard Smalley, a nanotechnology pioneer and the namesake of Rice’s Smalley Institute for Nanoscale Science and Technology. In 2003, Smalley worked with Pasquali and colleagues to create the first pure nanotube fibers. The work established an industrially relevant wet-spinning process for nanotubes that was analogous to the methods used to create high-performance aramid fibers, which are used in products such as bulletproof vests. The process, however, needed to be refined. The fibers weren’t very strong or conductive, due partly to gaps and misalignment of the millions of nanotubes inside them.
Through a refined process, today, the fibers have about 10 times the tensile strength and electrical and thermal conductivity of the best previously reported wet-spun CNT fibers, Pasquali said. The specific electrical conductivity of the new fibers is on par with copper, gold and aluminum wires, but the new material has advantages over metal wires.
For example, one application where high strength and electrical conductivity could prove useful would be in data and low-power applications, Pasquali said.
“Metal wires will break in rollers and other production machinery if they are too thin,” he said. “In many cases, people use metal wires that are thicker than required for the electrical needs, simply because it’s not feasible to produce a thinner wire. Data cables are a particularly good example of this.”
So, while products using this new carbon nanotechnology won’t be hitting the market next week, the new production method looks very promising and the potential is huge.