New nanotube fibers have unmatched combination of strength, conductivity, flexibility (w/ video)

Jan 10, 2013
Rice engineering professor Matteo Pasquali (seated) led a team that created a pure carbon nanotube fiber that combines the best features of metal wires, carbon fibers and textile thread. The team included (from left) Rice graduate students Colin Young and Dmitri Tsentalovich, Teijin Aramid scientist Ron ter Waarbeek and Rice graduate student Mohammed Adnan. CREDIT: Jeff Fitlow/Rice University

(Phys.org)—Rice University's latest nanotechnology breakthrough was more than 10 years in the making, but it still came with a shock. Scientists from Rice, the Dutch firm Teijin Aramid, the U.S. Air Force and Israel's Technion Institute this week unveiled a new carbon nanotube (CNT) fiber 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 fibers, which outperform commercially available high-performance materials in a number of ways.

"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 and strong ."

The research team includes academic, government and industrial scientists from Rice; Teijin Aramid's headquarters in Arnhem, the Netherlands; the Technion-Israel Institute of Technology in Haifa, Israel; and the Air Force Research Laboratory (AFRL) in Dayton, Ohio.

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Scientists have created the first pure carbon nanotube fibers that combine many of the best features of highly conductive metal wires, strong carbon fibers and pliable textile thread. In a Jan. 11 paper in the journal Science, researchers from Rice University, the Dutch firm Teijin Aramid, the US Air Force and Israel's Technion Institute describe an industrially scalable process for making the threadlike fibers, which outperform commercially available products in a number of ways. Credit: Rice University

"The new CNT fibers have a thermal conductivity approaching that of the best graphite fibers but with 10 times greater ," 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 markets."

The phenomenal properties of carbon nanotubes have enthralled scientists from the moment of their discovery in 1991. The 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 also can 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 threadlike fiber 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 fibers whole, but the production rates for these "solid-state" fibers 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.

Nanotubes are tightly packed in the new carbon nanotube fibers produced by Rice University and Teijin Aramid. This cross section of a test fiber, which was taken with a scanning electron microscope, shows only a few open gaps inside the fiber. CREDIT: D. Tsentalovich/Rice University

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 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—like Teijin's Twaron—which are used in bulletproof vests and other products. But the process 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.

"Achieving very high packing and alignment of the carbon nanotubes in the fibers is critical," said study co-author Yeshayahu Talmon, director of Technion's Russell Berrie Nanotechnology Institute, who began collaborating with Pasquali about five years ago.

The next big breakthrough 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," Pasquali said. "A graduate student in my lab, Natnael Bahabtu, found simple ways to show that CNT fibers could be spun from chlorosulfonic acid solutions. That was critical for this new process."

Pasquali said other labs had found that the strength and conductivity of spun fibers could also be improved if the starting material—the clumps of raw nanotubes—contained long nanotubes with few atomic defects. In 2010, Pasquali and Talmon began experimenting with nanotubes from different suppliers and working with AFRL scientists to measure the precise electrical and thermal properties of the improved fibers.

This light bulb is powered and held in place by two thin strands of carbon nanotube fibers that look and feel like textile thread. The nanotube fibers conduct heat and electricity as well as metal wires but are stronger and more flexible. CREDIT: Jeff Fitlow/Rice University

During the same period, Otto was evaluating methods that different research centers had proposed for making CNT fibers. He envisaged combining Pasquali's discoveries, Teijin Aramid's know-how and the use of long CNTs to further the development of high performance CNT fibers. In 2010, Teijin Aramid set up and funded a project with Rice, and the company's fiber-spinning experts have collaborated with Rice scientists throughout the project.

"The Teijin scientific and technical help led to immediate improvements in strength and conductivity," Pasquali said.

Study co-author Junichiro Kono, a Rice professor of electrical and computer engineering, said, "The research showed that the electrical conductivity of the fibers could be tuned and optimized with techniques that were applied after initial production. This led to the highest conductivity ever reported for a macroscopic CNT fiber."

The fibers reported in Science have about 10 times the tensile strength and electrical and of the best previously reported wet-spun CNT fibers, Pasquali said. The specific electrical conductivity of the new 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 far more thick 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."

Explore further: Researchers make nanostructured carbon using the waste product sawdust

More information: "Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity," by N. Behabtu et al. Science, 2013.

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User comments : 13

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Steven_Anderson
1 / 5 (2) Jan 10, 2013
anyone know what the exact strength of this material is?
EyeNStein
2 / 5 (4) Jan 10, 2013
How close are we to "space elevator" strength?
xeb
1 / 5 (1) Jan 10, 2013
Without buying an acces to Science :) .. Google returns this (only): "Tensile strength shows a 10-fold improvement over wet-spun fibers of 0.5-μm CNTs [~0.11 GPa (14)] and is comparable to the best .."
xeb
1 / 5 (1) Jan 10, 2013
So, (14) - must stand for some work in references, and that means they have reached ~1.1 GPa for fiber with 0,5-μm diameter (?). Wiki: "In 2000, a multi-walled carbon nanotube was tested to have a tensile strength of 63 gigapascals (GPa).[36] (For illustration, this translates into the ability to endure tension of a weight equivalent to 6422 kg (14,158 lbs) on a cable with cross-section of 1 mm2 [...] Although the strength of individual CNT shells is extremely high, weak shear interactions between adjacent shells and tubes leads to significant reductions in the effective strength of multi-walled carbon nanotubes and carbon nanotube bundles down to only a few GPa's" ... Work reported today improves this.
xeb
1 / 5 (1) Jan 10, 2013
Pls excuse to much posts. However, for those who want to know more and do not have Science account: http://www.scienc...u.SM.pdf this is 'suplementary materials' for the article :) ... And there are refeneces and tables - e.g. "Specific strength (mN/Tex)" and values: This work - 969, Steel - 267, Cytec Thornel®T-­‐650/35 carbon fiber (PAN-­‐based) - 2420, Collapsed
DWNTs fibers - 1800. And "Specific strength was calculated by dividing the tensile strength by the density of the fiber. Density was measured by weighing a 60 m long piece of fiber." "The highest measured breaking stress (tensile strength) was 1.3 GPa". However, i guess that lenght of individual CNTs is important here: "Fig. S6. Length distribution of as-received CNT material as measured by direct imaging with cryo-TEM. We measured a total of 41 individual CNTs and obtained an average length of 4.3 μm".
Jaeherys
1 / 5 (1) Jan 10, 2013
From the article,
"Tensile strength, modulus, and elongation to break (15) were determined from tensile break tests on macroscopic (~20 mm
long) individual filaments cut from large spools (~100 to 500 m)"

"The average tensile strength was 1.0 +- 0.2 GPa
(best value 1.3 GPa), and the average modulus was 120 +- 50 GPa"

"The average elongation at break for these fibers was 1.4 +- 0.5%"

"... high electrical conductivity...,on average 2.9 +- 0.3 MS/m (resistivity of 35 +- 3 microhm cm) at room temperature"

"[iodine doped version =] 5 +- 0.5 MS/m (resistivity 22 +- 4 microhm cm, best value of 17.5 microhm cm)"

"values were stable over 1 year in laboratory conditions and also under thermal cycling to 200°C in air for 24 hours"

"average thermal conductivity of 380 +- 15 W/m K on ~1.5-mm-long samples using the 3-omega method (15, 20). Iodine doping doubled thermal conductivity (635 W/m K). Such high thermal conductivity remains unchanged after annealing at 600°C"
PhysGeek
not rated yet Jan 11, 2013
So did anyone figure how close this gets us to a space elevator?
hb_
not rated yet Jan 11, 2013
Thank's Jaeherys for the Info!

Now, when I do the math, this fiber comes out 20 times less conductive than copper; really not "on par"... I also doubt that they can match the price of either copper or aluminum. So for me, the most interesting applications are out of reach.

If you could produce wires with a equal or higher conductivity compared to copper wires, you could make electical motors that are more light weight, has a higher power density and/or higher efficiency. That would be something!

As usual, though, it hinges on the cost. As far as I can tell from the scant information in the above article, they have not invented any revolutionary method of producing the nanotubes themselves, only invented a way to spin the nanotubes into fibers.
javjav
not rated yet Jan 11, 2013
So did anyone figure how close this gets us to a space elevator?

Yes there are some models about it. The link below correspond to P.K. Aravind, and it mentions 25GPa to start working, and 50GPa for a safety factor of 2

(although it still mention a few little issues that remain to be solved, including: "..vibrations in the cable induced by geophysical and astronomical sources, lightning strikes, meteors, space debris, wind, atomic oxygen, radiation, and erosion of the cable by sulfuric acid droplets in the upper atmosphere.."

http://users.wpi....tors.pdf
ValeriaT
1 / 5 (2) Jan 11, 2013
Osiris1
1 / 5 (1) Jan 11, 2013
This points to an emerging enabling technology, the mass production of ever larger and longer cables made up of these threads. They can have uses in better magnets for fusion and nuclear particle accelerator research, and can be used in electric propulsion drive ion accelerators, maybe to achieve thrust velocity in excess of 500,000 miles to a million miles/hour at high density for extremely high thrust. A Nuclear reactor powered shuttle may be able to take off and land with systems like this, and be able to control its descent to safer velocities as well. To hell with the politics, just do it. Our prez is in his second term anyway, and if we do not do it, our children had better start to learn Chinese so they will be good bed and house servants and good factory slaves and field hands for our new masters.
socean
not rated yet Jan 14, 2013
"The Chinese" will have robotic slaves thank you. You will be a pet, if you behave.
SteveL
not rated yet Jan 30, 2013
I wonder if they can use ceramic nano tubes and electromagnetism to align the carbon nanotube fibers for a more consistant alignment. I remember reading research more than 5 years ago, I think it was in Physics World, concluding that carbon nanotubes could be polarly aligned with such a process.