Orientation of carbon nanotubes in a sheared polymer melt

Optical measurements of the shear response of semidilute dispersions of polymer-dispersed multiwalled carbon nanotubes are presented. For a weakly elastic polymer melt, the data suggest that the semiflexible tubes orient along the direction of flow at low shear stress, with a transition to vorticity alignment above a critical shear stress, σc, corresponding to a critical Deborah number of approximately 0.15. In contrast, data for a highly elastic polymer solution suggest that the tubes orient with the flow field at high shear rates, in the limit of large Deborah number. The measurements are in qualitative agreement with previous experimental and theoretical studies of fiber orientation in elastic fluids under simple shear flow.