Optical microstructure and viscosity enhancement for an epoxy resin matrix containing multiwall carbon nanotubes

Abstract

This paper describes rheological measurements and associated optical microstructural observations of multiwall carbon nanotubes (MWCNTs) suspended in an epoxy resin matrix. The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near-complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected networks between nanotubes and or aggregates of nanotubes, and not by nanotube alignment.