Brownian dynamics simulations of polyelectrolyte adsorption in shear flow: Effects of solvent quality and charge patterning

We probe the effects of solvent quality and charge patterning on polyelectrolyte adsorption in shear flow using Brownian dynamics simulations with hydrodynamic interaction (HI). The polyelectrolyte is modeled as a freely jointed bead-rod chain, and electrostatic and non-electrostatic interactions are accounted for by using screened Coulombic and Lennard-Jones potentials, respectively. In the absence of flow, the conformation of a polyelectrolyte molecule adsorbed onto a uniformly charged surface changes from flat to globular with an increase in bead-bead attraction (hydrophobicity), consistent with prior experimental observations. In the presence of flow, migration due to bead-wall HI and, as a consequence, desorption decrease with an increase in bead-bead attraction, implying that flow-induced desorption is more difficult under poor-solvent conditions. When bead-bead non-electrostatic attraction is strong, desorption can be enhanced by increasing bead-bead electrostatic repulsion. Analogous to the effect of bead-surface electrostatic attraction, an increase in the strength of bead-surface non-electrostatic attraction reduces desorption. We also study the effect of shear flow on the adsorption of a polyelectrolyte molecule onto surfaces decorated with periodic arrays of charged patches. An increase in patch periodicity increases desorption even when the effective surface charge density is kept the same. The results of this work suggest mechanisms for controlling the desorption of polyelectrolyte molecules in shear flows. (c) 2008 American Institute of Physics.