(284a) Polyelectrolyte Adsorption in Shear Flow with Hydrodynamic Interactions: Kinetic Theory and Brownian Dynamics Simulations

Authors: 
Hoda, N. - Presenter, University of Michigan


The effect of hydrodynamic interactions on the adsorption of a polyelectrolyte molecule onto a wall in shear flow is investigated using kinetic theory and Brownian dynamics simulations. A bead-spring dumbbell model is used in the kinetic theory, while both bead-rod and bead-spring chains are investigated in the Brownian dynamics simulations. In the kinetic theory, bead-bead and bead-wall electrostatic interactions are taken into account using screened Coulombic interactions, and the hydrodynamic interactions are incorporated using the approach proposed by Ma and Graham [Phys. Fluids. 17, 083103 (2005)]. An analytical expression for the concentration profile of the polyelectrolyte is derived which predicts a competition between bead-wall hydrodynamic interactions and bead-wall electrostatic attraction. The behavior of the concentration profile is explored as a function of the Weissenberg number, surface (wall) charge density, charge on the beads, and screening length. The charge on the beads assists migration of the dumbbell away from an uncharged wall, whereas for an oppositely charged wall it increases the probability of finding the dumbbell close to the wall. In some cases, the concentration profile shows a very sharp peak near the wall whose distance from the wall increases with dumbbell size, indicating the possibility of size-based separation. The results of the Brownian dynamics simulations are consistent with the kinetic theory, and are used with the kinetic theory to develop a criterion for the critical shear rate needed to desorb an adsorbed polyelectrolyte molecule. The results of this work are expected to be of interest for applications related to materials science, microfluidics, and biophysics.