How does length of alkyl hydrocarbon chains on zwitterion functionalised multiwalled carbon nanotubes influence dispersion of carbon nanotubes?

Abstract

Zwitterion functionalisation is carried out to alter surface properties and hence disperability of carbon nanotubes by attaching short and long alkyl hydrocarbon chains onto the nanotubes. Long chain attachment results in long term stabilisation of the carbon nanotubes in toluene, whereas short chain simply enhances their dispersion. Small angle light scattering is used to measure the dispersion of the carbon nanotubes suspended in toluene. Analysis of these data elucidates the mechanism by which the functionalisation assists in the dispersion and ultimately leads to the long term stabilisation of the nanotubes in toluene. Functionalised and untreated nanotubes exhibit hierarchical morphology consisting of small scale aggregates (bundles) that form fractal agglomerates. The bundles consist of multiple tubes possibly aggregated side by side. The bundle morphology and agglomeration of the bundles are quite dependent on functionalisation. In the case of long solubilising chain attachment, the small scale aggregates are broken up into smaller sizes, and no agglomeration is observed over months, whereas the short chain nanotubes agglomerate and eventually precipitate out of solution in several days. For untreated tubes, large agglomerates appear immediately after cessation of sonication. Functionalisation leads to the long term stabilisation of the nanotubes, not only by inhibiting agglomeration but also by breaking up the side by side bundles.