DISPERSION AND PACKING OF CARBON NANOTUBES

Suitable oxidative treatment of catalytically grown carbon nanotubes i ntroduces oxygen containing surface groups. Infrared and titration stu dies indicate that they are predominately phenolic, carboxylic and lac tonic groups. These groups stabilize dispersions of nanotubes at much higher concentrations than are possible with the raw material. Plots o f the viscosity of dispersions as a function of their concentration sh ow a dramatic increase in gradient above a critical concentration, lea ding to the formation of viscoelastic gels. During continued drying, t he solvent mediates the formation of dense assemblies of nanotubes whi ch then bond together through the surface groups. If the nanotubes are deposited from a dilute suspension by filtration they are able to max imize the number of intertube contacts by packing into a locally paral lelized structure, reminiscent of liquid crystalline polymers. (C) 199 8 Elsevier Science Ltd. All rights reserved.