Figure 5. Scanning electron micrographs of the epoxy matrix composite
materials reinforced with single-walled carbon nanotubes.
The scanning electron micrographs of the epoxy matrix composite
materials are illustrated in Figure 6 which are reinforced with
multi-walled carbon nanotubes. The use and development of carbon
nanotubes has expanded [69, 70]. These materials are valuable in
next generation industries including the fields of electronics and
chemistry [71, 72]. The further development of carbon nanotube
technology allows organized structures or intertwined randomly oriented
bundles of carbon nanotubes to be formed [73, 74]. Techniques have
been developed to controllably build organized architectures of carbon
nanotubes having predetermined orientations, such as vertically aligned
carbon nanotubes [75, 76]. Although such structures may be useful
for a variety of purposes, the structures by themselves may be limited
in terms of function and application [77, 78]. The structure is a
combination of dispersed multi-walled carbon nanotubes and micron-scale
agglomerates. On the fracture surface, multi-walled carbon nanotubes are
pulled-out of the matrix, indicating that there is likely energy
dissipation from interfacial debonding and pullout of the multi-walled
carbon nanotubes. Outside the area where multi-walled carbon nanotubes
are locally agglomerated the fracture surface is quite smooth, similar
to that of the unreinforced epoxy. Where the multi-walled carbon
nanotubes are present it is clear that there is an increase in surface
roughness. In the areas where multi-walled carbon nanotubes are
agglomerated, tail-like structures are formed. These features indicate
that the multi-walled carbon nanotubes interact with the crack path and
result in crack deflection and a more torturous fracture path. Some
multi-walled carbon nanotube pullout as well as texturing of the
fracture surface, but the formation of the larger-scale tail structures
is not present. A possible reason for the overall higher fracture
toughness for the structure that contains both dispersed and
agglomerated features may be a result of larger agglomerates being able
to more effectively interact with the crack front.