Dispersion of Carbon Nanotubes
Carbon nanotubes are the strongest and most conductive materials known to man. These properties make them ideal as fillers in advanced polymer based composite materials. However, due to their high surface energy they generally aggregate together to form bundles. These bundles are mechanically and electrically inferior to individual nanotubes and unsuitable for composite applications. It will be crucial for us to debundle nanotubes in order for them to reach their full potential.
Most of the composite formation we do is carried out in solution. This involves mixing polymer and nanotubes in an appropriate solvent. Early on the polymer choice was limited by the fact that the polymer had to act as a dispersant to stabilize the nanotubes against sedimentation (see paper 8 and 25). A good polymer dispersant not only stabilizes the nanotube dispersion but acts to debundle the nanotubes (see paper 46).
Figure 1 Histrogram of bundle diameter distributions for nanotubes dispersed in NMP at different concentrations nanotube (see paper 69)
However it was recently observed that a small number of solvents, such as NMP and DMF, can actually disperse nanotubes without the need for any additional dispersant molecules. We have recently shown that, in addition to stably dispersing nanotubes, NMP can actually debundle nanotubes down to the level of individual tubes. In fact at low concentration as much as 80% of the dispersed objects are individual tubes (see paper 69).
We have discovered 14 other solvents and are in the process of investigating the mechanism of dispersion.
Figure 2 Photoluminesence contour map of SWNT dispersed in NMP(see paper 69)
In addition we are studying bio-molecules as dispersants. The focus of this work so far has been to demonstrate that cheap and abundant natural DNA can not only disperse nanotubes but also debundle. In addition we are studying the role of chain length in the dispersion of nanotubes by synthetic DNA and the dispersion of nanotubes by synthetic peptides.
Figure 3 AFM images of Salmon testes DNA wrapped SWNT deposited on mica