Extension-induced dispersion of multi-walled carbon nanotube in non-Newtonian fluid

In this study, we devised an extension-induced mixer to disperse carbon nanotube (CNT) clumps into individual tubes by imposing extensional stress continuously and periodically. The rheological behavior of the CNT-dispersed suspension was investigated to examine whether the hydrodynamic dragging induces the dispersion of individual CNT from strongly entangled CNT by van der Waals force between adjacent tubes. When CNT clumps were subjected to a continuous extensional flow for a prolonged time, the optical microscopic and cryo-transmission electron microscopy studies showed that the CNT agglomerates were effectively dispersed and some of the individual nanotubes were disentangled from the CNT clump. Shear viscosity of the dispersion increased when the CNT-Boger fluid suspension was subjected to the continuous and periodic extensional flow for a prolonged time, indicating the dispersion of the individual tubes by the extensional flow. Under shear flows, however, aggregated CNT clumps formed larger, weakly bound agglomerates with diameters up to millimeters. The newly suggested mixing technique can be used effectively for mixing two different kinds of polymers with a large difference in viscosity.