Nanotube Composite Carbon Fibers

The mechanical properties of materials in small rod-shaped form are of considerable technological interest since, due to their shape and size, they can exhibit appreciably greater strength relative to corresponding macroscopic forms. For example, the mechanical strength of silicon carbide whiskers systematically increases with decreasing whisker diameter over the 100 to 1 micron range. This phenomenon has been attributed to a reduction in the number of structural defects that can lead to mechanical failure. In the past decade, we have seen a tremendous level of activity in the field of nanostructural materials, fueled by breakthroughs in synthesis and the promise of unique applications. In particular, carbon nanotubes, which are closed, elongated carbon cages of pure carbon (Fig. 1a), are believed to have mechanical and electrical properties that are unmatched by any material. The structure of carbon nanotubes can be viewed as a single sheet of graphite (Fig 1b) wrapped into a seamless cylinder of several microns in length and ~1 nm in diameter. The curvature of the hemispherical end-caps (Fig. 1c) which close the tube is obtained by the introduction of six pentagons into the hexagonal structure of graphite. Figure 1a shows a single-walled carbon nanotube. However, unless they are synthesized under specific conditions and in the presence of a metal “catalyst,” carbon nanotubes are formed as a series of nested or multiwalled tubes (Fig. 1d). The extraordinary properties of carbon nanotubes derive from the special arrangement of the carbon bonds in these quasi-one-dimensional structures. To date, suitable methods for the direct measurement of nanotube properties, such as, instrumentation to break a single nanotube under tension, do not exist. In the interim, computer modeling aimed at predicting their physical properties reveals that the tiny carbon nanotubes are also mighty when compared on a nanometer scale, they are a hundred times stronger than steel and only one-sixth its weight.