(247g) Effect of Flexibility on the Shear-Induced Migration of Short Polymers in Parabolic Channel Flow

There is now considerable evidence, both experimental (Chen et al. 2004, Fang et al. 2005) and via computer simulation (Jendrejack et al. 2003, 2004, Chen et al. 2004, Usta et al. 2005) that long-chain flexible polymers migrate toward the center line in plane Poiseuille flow owing to hydrodynamic interactions with the wall. The mechanism for this migration has recently been summarized by Ma and Graham 2005. Computational studies of rigid rod polymers (dePablo et al. 1992, Schiek and Shaqfeh 1997) have not included these hydrodynamic interactions and therefore have focused on migration toward the wall as a result of the configuration-dependent diffusivity that results from increased flow alignment in the near wall, high shear regions. To connect the studies of highly flexible polymers with those of rigid rod polymers, we study the effect of chain flexibility on the shear-induced migration of short polymers in a pressure-driven flow between two infinite flat plates. We have implemented a Brownian dynamics algorithm that models a polymer molecule as a chain of N freely jointed Brownian rods and includes multibody hydrodynamic interactions between the chain segments and channel walls. Our simulations confirm the existence of shear-induced migration away from the solid boundaries toward the channel centerline as a result of wall hydrodynamic interactions, but we show the mechanism of this migration differs substantially if the chain is a rigid rod as opposed to a flexible thread. Thus the primary effect for very rigid polymers is still migration toward the walls. For flexible chains, we show that at a fixed ratio h/Rg of the channel width to the bulk radius of gyration, and at a fixed value of the Weissenberg number Wi, the migration is not significantly influenced by flexibility for the chain lengths considered in this work.