A rheological study of concentrated aqueous nanotube dispersions

The rheological behaviour of aqueously dispersed oxidised nanotubes has been studied at concentrations at which the nanotubes interacted with each other. The dispersed nanotubes represented a high aspect ratio system with a ratio of ∼80. Dynamic and steady shear tests were applied to the dispersions using a cone and plate rheometer. The system was found to behave as a reversibly flocculated dispersion. The structure of the dispersions was highly strain-sensitive with the linear viscoelastic region (LVR) extending to strains of 1%. The moduli within the LVR were independent of frequency and scaled with concentration by a power law. Under steady shear the dispersions rapidly shear thinned up to a Peclet number of ∼1 to 10. At higher Peclet numbers the shear thinning behaviour followed the Ostwald–de Waele power law. The dispersions were thixotropic and recovered their structure, and hence viscosity, upon standing.