2012 Volume 40 Issue 2 Pages 101-109
We herein describe our investigation of the rheological and electrical characteristics of single- and multi-walled carbon nanotube dispersions. The effect of the viscosity of the dispersing liquids was investigated under shear. At low shear rates, a dispersing liquid with a low viscosity caused the relative viscosity to increase more than a dispersing liquid with a high viscosity, in the case of single-walled carbon nanotube dispersions. The shear viscosity approached the same value regardless of the viscosity of the dispersing liquid. The independence of the shear viscosity suggests that at low shear rates it is dominated by the microstructure of the single-walled carbon nanotubes rather than the viscosity of the dispersing liquid. Extensional flow was produced by the capillary thinning of a liquid thread, and both the apparent extensional viscosity and the electrical conductivity were measured for the carbon nanotube dispersions. During capillary thinning, the apparent extensional viscosity approached the theoretical extensional viscosity predicted by Batchelor for low concentrations, but was notably higher than the theoretical values predicted for high concentrations. The electrical conductivity was increased via the stretching of the threads and the solidification of the dispersing photopolymer. The concentration at the electrical percolation threshold was approximately the same as the concentration at which the apparent extensional viscosity deviated from the theoretical prediction of Batchelor. A network structure of carbon nanotubes is herein suggested to increase the apparent extensional viscosity at concentrations above the percolation threshold.
