Carbon nanotube fibers

Paris, November 16, 2000

CNRS researchers* and scientists at the University of Bordeaux 1 have recently developed a process for producing macroscopic carbon nanotube fibers and strips. This breakthrough will allow the technological properties of carbon nanotubes, which up to now have simply been a laboratory curiosity, to be explored.

To date, two major obstacles have impeded the development of technological research on carbon nanotubes: their preparation and their formation. Researchers worldwide are working on optimizing the synthesis of carbon nanotubes.

The team at the CNRS "Centre de recherche Paul Pascal" (CRPP, Paul Pascal Research Center) has been working on overcoming the obstacle to the formation the carbon nanotubes and has developed a process for aligning them in the form of fibers and strips. This process was patented in February 2000. In addition, researchers in the "Groupe de dynamique des phases condensées"** (GDPC, Condensed Phase Dynamics Group) in Montpellier have developed an electric arc method for producing nanotubes. A company by the name of Nanoledge (trade mark), is being created*** to capitalize on their know-how. CRPP’s research team has used materials synthesized by the Montpellier group to obtain carbon nanotube fibers with a diameter on the micrometer scale and a length of a few centimeters. Automation of the process, in partnership with Nanoledge and the GDPC, should eventually enable spools of nanotube fibers to be manufactured and thus it will be possible to test their properties, in particular their mechanical properties, on a natural scale.

Figure 1 :Carbon nanotube observed under an optical microscope (approximate width of strip: 0.5 mm). © CNRS		Figure 2 : Optical microscope observation of a dense nanotube fiber (scale: the white line corresponds to 25 microns). © CNRS

The patented process is based on the Paul Pascal Research Center’s know-how in the field of colloidal suspensions: nanotubes, which are hydrophobic (i.e., they repel water) colloidal (submicrometric) particles, are dispersed in water using a surfactant (detergent). This homogeneous dispersion is then extruded into a viscous solution containing a polymer that destabilizes the suspension and aggregates the nanotubes into narrow strips. These strips, a few microns thick and a few millimeters wide, are made up of entangled nanotubes with a preferred orientation due to the direction of extrusion, as shown under the optical microscope (Figure 1) and the electron microscope. These strips contract when dried in air and the water they contain is evacuated by capillary action, forming dense fibers (Figure 2). The mechanical properties of this new type of fiber are currently being optimized by CRPP and will show whether in the future they could compete with existing very high performance carbon fibers. Right now, these nanotube fibers exhibit high resistance to forces perpendicular to their axis, in contrast to conventional carbon fibers. This can readily be demonstrated by a simple experiment: the fibers are knotted (Figure 3) then pulled. The majority of conventional carbon fibers break instantaneously, while nanotube fibers are more resistant, although they too eventually break, at a distance from the knot.

Figure 3 : Knotted nanotube fibers (approximate fiber diameter: 10 microns).

Depending on the performance of and improvements made to this very recent discovery, researchers may be able to develop a multitude of applications, such as: artificial muscles, nanotube fiber textiles, supercondensors for electric vehicles, electron emitters for flat screens, etc. Even if they prove possible, these applications will not see the light of day until the cost (currently of the order of 6000 FRF/g) has fallen. Demonstrating the technological feasibility of applications based on nanotube fibers, though, should help to motivate the carbon industry to increase production capacity by several orders of magnitude and thereby reduce costs.

This work, patented in February 2000, was published in Science on 17th November 2000

References:
Process for producing macroscopic fibers and strips, in particular carbon nanotubes, from colloidal particles. P. Poulin, B. Vigolo, A. Pénicaud, C. Coulon, CNRS, French patent application number 0002272.

* Centre de recherche Paul Pascal (CRPP, Paul Pascal Research Center, CNRS-UniversitŽ Bordeaux 1)
** CNRS-UniversitŽ des Sciences et Techniques du Languedoc (Languedoc University of Science and Technology)
*** Under the co-operative scheme initiated in 1999 by the Minister for National Education, Research and Technology.

Carbon nanotubes

Crystalline (diamond and graphite) and amorphous (carbon black, pyrocarbon, etc.) forms of carbon have pride of place among technological materials – think of the abrasive properties of diamonds, the lubricating properties of graphite, and the performance of carbon fibers, with a micro-graphite structure, used in many applications because of their exceptional mechanical properties. Two new forms of carbon have recently been discovered: fullerenes in 1985, by an Anglo-American team, and nanotubes in 1991, by a Japanese team. A nanotube is a cylinder with a graphite structure (curved, like a roll of chicken wire) and closed at both ends by a fullerene type cap, i.e., containing pentagons (Figure 4). These cylinders can be a few microns or even millimeters long, with a diameter of the order of a nanometer (10-9 m) – hence their name. They constitute the ultimate carbon fibers and as a result, they have sparked scientists' imaginations. Depending on the detailed structure (diameter, twist, etc.), these nanotubes are electrical conductors or semi-conductors. These properties, combined with their size, enable new micro-electronics applications to be envisaged. Furthermore, carbon nanotubes are expected to have exceptional mechanical properties (they are a hundred times stronger and six times lighter than steel) and thus could form the basis of a multitude of future high performance materials.

Figure 4 : Diagrammatic representation of a nanotube: cylinder with a graphite structure closed at both ends by a fullerene type cap (containing pentagons).

Researcher contacts:
Centre de recherche Paul Pascal (CRPP)
CNRS-Université Bordeaux 1
Alain PENICAUD
e-mail: penicaud@crpp.u-bordeaux.fr
Philippe POULIN
e-mail: poulin@crpp.u-bordeaux.fr

CNRS Department of Chemical Sciences contact:
Laurence MORDENTI,
tel.: (33) 1 44 96 41 09
e-mail: laurence.mordenti@cnrs-dir.fr