(232k) Migration Mechanisms for Rigid Polymers and Nanorods Sheared at High Peclet Number

Mechanisms leading to the net migration for rigid, Brownian rods sheared at high rates are explored. At these large, but finite, values of the Peclet number, the competition between the randomization caused by Brownian rotation and tendency of the shearing flow to align the rods breaks the symmetry about the flow direction of the orientation distribution. The asymmetric distribution of the rod's orientation can then couple with inhomogeneous shear flows to generate a net migration. Examples include the migration away from bounding walls in simple shear flow and Poiseuille flow, where the inhomogeneous field is produced by hydrodynamic interactions with the walls, as well as the net migration of rods toward the axis of rotation in torsional flows. These effects are not inertial, as the studies are performed under the conditions of Stokes flow and each mechanism is analogous with similar phenomena for flexible polymers, though the rigid rods require a much higher value of the Peclet number before the migration becomes significant. Rheological impacts of the migration mechanism are slight for the case of simple shear flow, but can be significant for torsional flows.