Dispersion and packing of carbon nanotubes

Suitable oxidative treatment of catalytically grown carbon nanotubes introduces oxygen containing surface groups. Infrared and titration studies indicate that they are predominately phenolic, carboxylic and lactonic groups. These groups stabilize dispersions of nanotubes at much higher concentrations than are possible with the raw material. Plots of the viscosity of dispersions as a function of their concentration show a dramatic increase in gradient above a critical concentration, leading to the formation of viscoelastic gels. During continued drying, the solvent mediates the formation of dense assemblies of nanotubes which then bond together through the surface groups. If the nanotubes are deposited from a dilute suspension by filtration they are able to maximize the number of intertube contacts by packing into a locally parallelized structure, reminiscent of liquid crystalline polymers.