Brownian dynamics simulations are used to study the adsorption of an isolated polyelectrolyte molecule onto an oppositely charged flat surface in the absence and the presence of an imposed shear flow. The polyelectrolyte is modeled as a freely jointed bead-rod chain where excluded volume interactions are incorporated by using a hard-sphere potential. The total charge along the backbone is distributed uniformly among all the beads, and the beads are allowed to interact with one another and the charged surface through screened Coulombic interactions. The simulations are performed by placing the molecule a fixed distance above the surface, and the adsorption behavior is then studied as a function of screening length. In the absence of an imposed flow, the chain is found to lie flat and extended on the adsorbing surface in the limit of weak screening, whereas in the limit of strong screening it desorbs from the surface and attains free-solution behavior. For intermediate screening, only a small portion of the chain adsorbs and it becomes highly extended in the direction normal to the surface. An imposed shear flow tends to orient the chain in the direction of flow and also leads to increased contact of the chain with the surface.
Bibliographical noteFunding Information:
This material is based upon work supported in part by the U. S. Army Research Laboratory and the U. S. Army Research Office under Grant No. W911-NF-04-1-0265. Our work was also supported in part by the Army High Performance Computing Research Center under the auspices of the Department of the Army, Army Research Laboratory (ARL) under Cooperative Agreement No. DAAD19-01-2-0014. The content does not necessarily reflect the position or policy of the government, and no official endorsement should be inferred.