Flow Induced Orientation Behavior of Concentrated Dispersions of Multi-Walled Carbon Nanotube Suspension Under Shear Flow

We report studies of average orientation state of concentrated dispersions of multi-walled carbon nanotube (MWNTs) in steady shear flow. Uncured epoxy was used as a viscous, Newtonian suspending medium, and samples were prepared from 'aligned' MWNTs using methods previously reported (Rahatekar et al., J Rheol 40:599, 2006). Flow induced structural measurements were made on a number of samples in the vorticity (1-3) plane of simple shear flow using in-situ x-ray scattering techniques in a rotating disc shear cell. Steady state anisotropy of MWNT dispersions decrease with increasing the length of the MWNTs. Surprisingly, the anisotropy is seen to increase with increasing concentration. For one of the samples (2wt% short MWNT), much detailed orientation dynamics is studied in steady shear and transient shear flow both in the 1-2 (flow gradient) and 1-3 (vorticity) planes of shear flow using small and wide angle x-ray scattering. Anisotropy induced in the 1-2 plane is found to be higher than anisotropy induced in the 1-3 plane. WAXS yields quantitatively a higher value of anisotropy than SAXS in the 1-3 plane. Measurements in 1-2 plane are done using an annular cone and plate x-ray shear cell.