1.3. Carbon Nanotubes for Composite Applications
1.3.1. Challenges in Preparing Randomly-Aligned Nanocomposites
No matter the matrix material one is attempting to reinforce with CNTs or
any nanoscale material, the greatest challenge in nanocomposite preparation is
arguably in dispersion. While surface-area-to-mass ratio is the origin of their
advantage over traditional materials, it is the predominant factor which leads to the
agglomeration of nanomaterials. CNTs are no exception to this, as they have been
observed to readily form rope-like structures both after growth and in solution;
these CNT ropes are very difficult to break apart due to the Van der WaaIs attraction
between such atomically pristine surfaces, and the use of strong acids such as
fuming sulfuric acid (oleum) is one of the only methods by which to intercalate
these dense bundles [23].
Agglomeration is a real issue in the manufacturing of nanocomposites, and
for more than one reason. Firstly, the special properties of these nanomaterials are
largely dependent on their size and/or structure. When they agglomerate and
aren’t homogeneously dispersed in a particular medium, much of their advantage is
lost. Along those lines, while they are remarkably difficult to separate, the
interactions between these nanoparticles are inherently weak since the attraction is
predominantly orthogonal to the surface. Put simply, agglomerates are highly
susceptible to shear forces and can easily slide past each other. Inside of a matrix,
such sliding significantly threatens the bulk structural integrity under loading. This
issue is amplified for CNTs due to their extremely high aspect ratio (eg. 10,000:1 for