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Carbon Nanotube Textile

May 25, 2017

One childhood memory I have is the visage of a strange little bridge on the road between our house and the downtown area. The bridge crossed the Mohawk River, a span of just 250 feet. What was strange about that bridge was the pair of short girder arches on the sides of the otherwise contiguous road surface. This bridge didn't really look like a bridge, and I always thought that the girders were decorative, or a way to separate the roadway from the sidewalk. That was before I learned about truss bridges.

Example of a pony truss bridgeAn example of a pony truss bridge at Tacuarembó, Uruguay.

The bridge of my childhood wasn't as colorful, being a uniform light green color.

(Via Wikimedia Commons.)

Rather thick beams would have been required to carry the weight of a roadway over such a gap. Lesser materials served the same purpose by changing the one-dimensional beams into a two-dimensional structure. Common I-beams were riveted together to create a type of truss bridge called a "pony truss" bridge, an inexpensive structure suited for such a short span. It's no surprise that the dominant geometrical element of a truss is the triangle.

As I explained in a previous article (Non-Brittle Ceramic Structures, November 21, 2014), while a quadrilateral assembled from equal length pieces can have a variety of angles, the angles of a triangle are fixed by their lengths. This property leads to the dimensional stability of structures built from triangles (see figure).

Demonstration of triangle rigidity
Three equal sides will assemble into only one triangle, but four equal sides can assemble into quadrilaterals of various angles, such as a square (center) and a rhombus (right). The transition from a square to a rhombus is often used as an example of shear. (Created using Inkscape.)

While pony truss bridges are rare, an example of a truss with a long history is probably near where you're seated. In 1839, Camille Polonceau, a French railway engineer, invented the eponymous Polonceau truss, as shown in the figure. This truss is a common element of roof construction. In honor of his invention, Polonceau's name was among the 72 names engraved on the Eiffel Tower, joining such scientific luminaries as Cauchy, Coriolis, Coulomb, Gay-Lussac, Fourier, Lagrange, Laplace, and Lavoisier.

Polonceau trussThe power of the triangle.

A Polonceau truss.

(Wikimedia Commons image by Christophe Dang Ngoc Chan.)

The idea that linear structural elements can be assembled into strong two-dimensional structures is especially important in the nanoscale realm. Multi-walled carbon nanotubes have shown themselves to be individually strong, with tensile strength about two orders of magnitude greater than that of stainless steel.[1] Among other benefits, carbon nanotubes are lighter than aluminum, and more conductive than copper. The utility of these exceptional properties can only be realized in practice when these carbon nanotubes can be joined together to form larger structures.

The problem, of course, is how do you "glue" nanotubes together? A research team from the Department of Mechanical Science and Engineering at the University of Illinois Urbana-Champaign has produced a tough conductive textile by "capillary splicing" of carbon nanotubes.[2-3] While the term, "capillary splicing," is used for the technique in which things such as fiberoptic cables are joined through insertion into the separate ends of a capillary tube, the Illinois technique uses capillary action in a more general sense. Surfaces will attract each other in order to reduce their surface energy, the difference in energy between surface atoms and atoms in the bulk of a material. Einstein's first publication was on capillary action.[4]

As mobile devices become smaller, there's a push to make them flexible, as well, but flexure of electrical conductors is only possible when they resist fracture. The Illinois team was able to achieve high strength in a nanotube fabric by alignment of the nanotubes on a substrate, where they couple together through strong van der Waals forces.[2] the average strength of the as-prepared nanotube fabric was 170 MPa, and its average fracture energy was 16 kJ/m2, values that are fifty times higher than those for metal nanofilms.[2]

To produce their textile of carbon nanotubes, they first deposited a catalyst on a Silica glass substrate. The catalyst was deposited as a staggered pattern not unlike that seen in brickwork, and in tough natural materials such as nacre and bamboo.[3] Then, vertically-aligned carbon nanotubes were synthesized by chemical vapor deposition to produce parallel lines of 5 μm width, 10 μm length, and 20-60 μm height.[3] This nanotube array was then coated with polyvinyl alcohol and polymethyl methacrylate (PMMA).[3] When the substrate was floated onto water, the PMMA carrier film was released.[2] acetone was used to dissolve the PMMA after this film was mounted for tensile testings to produce a bare nanotube textile.[2]

Overlap of nanotubes in nanomeshScanning electron microscope image of the carbon nanotube textile, with a high resolution inset image showing the inter-diffusion.

The colored schematic shows the self-weaving nanotube structure.

(University of Illinois College of Engineering image.)

Says Sameh Tawfick, an assistant professor of mechanical science and engineering at Illinois,
"To our knowledge, this is the first study to apply the principles of fracture mechanics to design and study the toughness of nano-architectured CNT textiles. The theoretical framework of fracture mechanics is shown to be very robust for a variety of linear and non-linear materials... Flexible electronics are subject to repeated bending and stretching, which could cause their mechanical failure. This new CNT textile, with simple flexible encapsulation in an elastomer matrix, can be used in smart textiles, smart skins, and a variety of flexible electronics."[3]

Stress-strain curve for carbon nanotube textile.Representative stress-strain curve for the carbon nanotube textile.

(Portion of a University of Illinois College of Engineering image.)

Partial funding for this research came from the Office of Naval Research.[2]


  1. Mechanical properties of carbon nanotubes Web Page on Wikipedia.
  2. Yue Liang, David Sias, Ping Ju Chen, and Sameh Tawfick, "Tough Nano‐Architectured Conductive Textile Made by Capillary Splicing of Carbon Nanotubes," Advanced Engineering Materials, Early View Article (March, 2017), DOI: 10.1002/adem.201600845.
  3. Rick Kubetz, "Wonder material? Novel nanotube structure strengthens thin films for flexible electronics," University of Illinois Urbana-Champaign Press Release, April 21, 2017.
  4. Albert Einstein, "Folgerungen aus den Capillaritätserscheinungen," Annalen der Physik, vol. 309, no. 3 (1901), pp. 513-523, doi:10.1002/andp.19013090306. A page image file can be found here.

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