Researchers at Teijin Aramid in the Netherlands and Rice University in the USA, the U.S. Air Force and Israel’s Technion Institute have this week unveiled a new carbon nanotube (CNT) fibre that looks and acts like textile thread and conducts electricity and heat like a metal wire. In this week’s issue of Science, the researchers describe an industrially scalable process for making the threadlike fibres, which outperform commercially available high-performance materials in a number of ways.
Lead researcher Matteo Pasquali, professor of chemical and biomolecular engineering and chemistry at Rice said;
We finally have a nanotube fibre with properties that don’t exist in any other material, It looks like black cotton thread but behaves like both metal wires and strong carbon fibres.
Carbon nanotubes, the building blocks of the fibre, which is as thin as a strand of DNA, combine the best properties of thermal and electrical conductivity, strength, modulus and flexibility.
The new CNT fibres have a thermal conductivity approaching that of the best graphite fibres but with 10 times greater electrical conductivity, Graphite fibres are also brittle, while the new CNT fibres are as flexible and tough as a textile thread. The researchers 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 enthralled scientists from the moment they were discovered in 1991. The hollow tubes of pure carbon, which are nearly as 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 can also serve as light-activated semiconductors, drug-delivery devices and even sponges to soak up oil.
Unfortunately, carbon nanotubes are also the prima donna of nanomaterials; they are difficult to work with, despite their exquisite potential. For starters, finding the means to produce bulk quantities of nanotubes took almost 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.
Creating large-scale objects from these clumps of nanotubes has been a challenge. A thread like fibre that is less than one-quarter the thickness of a human hair will contain tens of millions of nanotubes packed side by side. Ideally, these nanotubes will be perfectly aligned — like pencils in a box — and tightly packed. Some labs have explored means of growing such fibres whole, but the production rates for these “solid-state” fibres have proven quite slow compared with fiber-production methods that rely on a chemical process called “wet spinning.” In this process, clumps of raw nanotubes are dissolved in a liquid and squirted through tiny holes to form long strands.
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, two years before his untimely death, Smalley worked with Pasquali and colleagues to create the first pure nanotube fibres. The work established an industrially relevant wet-spinning process for nanotubes that was analogous to the methods used to create high-performance aramid fibres — like Teijin’s Twaron — which are used in bulletproof vests and other products. But the process needed to be refined. The fibres weren’t very strong or conductive, due partly to gaps and misalignment of the millions of nanotubes inside them.
The next big landmark came in 2009, when Talmon, Pasquali and colleagues discovered the first true solvent for nanotubes chlorosulfonic acid. For the first time, scientists had a way to create highly concentrated solutions of nanotubes, a development that led to improved alignment and packing.
Until that time, no one thought that spinning out of chlorosulfonic acid was possible because it reacts with water, A graduate student in my lab, Natnael Bahabtu, found simple ways to show that CNT fibres could be spun from chlorosulfonic acid solutions. That was critical for this new process.
The fibres reported in Science have about 10 times the tensile strength and electrical and thermal conductivity of the best previously reported wet-spun CNT fibres, Pasquali said. The specific electrical conductivity of the new fibres is on par with copper, gold and aluminium wires, but the new material has advantages over metal wires.