Single microbundle

The fractal-like organization led, therefore, to conductivity measurements at three different scales (1) the macroscopic, mm-size core of nanotube containing material, (2) a large (60 nm) bundle of nanotubes and, (3) a single microbundle, 50 nm in diameter. These measurements, though they do not allow direct insights on the electronic properties of an individual tube give, nevertheless, at a different scale and within certain limits fairly useful information on these properties. 

Fig. 5. Electrical resistance as a function of the temperature at the indicated magnetic fields for a single microbundle of carbon nanotubes. The solid line is a fit using the two-band model for graphite (see inset) with an overlap A = 3.7 meV and a Fermi level right in the middle of the overlap (after Langer et at. l9 ).

In view of the fact that the above techniques examine single fibers embedded in a matrix block, application of the experimental measurements to practical fiber composites may be limited to those with small fiber volume fractions where any effects of interactions between neighboring fibers can be completely neglected. To relate the interface properties with the gross performance of real composites, the effects of the fiber volume fraction have to be taken into account. To accommodate this important issue, a modified version of the fiber pull-out test, the so-called microbundle pull-out test, has been developed recently by Schwartz and coworkers (Qui and Schwartz, 1991, 1993 Stumpf and Schwartz, 1993 Sastry et al., 1993). In... 

---