(337b) Molecular Dyamics Simulations Of Dynamic Coatings For Quenching Electroosmotic Flow

The suppression of electroosmotic flow (EOF) through the use of a dynamically adsorbed polymer coating is a widely used technique in micro- and nano-fluidics, particularly for capillary electrophoresis. Recent experimental evidence has suggested that the most effective coatings are those which are only weakly adsorbed to the surface. This is because the suppression of the EOF depends on the amount of polymer which stretches from the surface through the debye layer and into the bulk and not the friction felt between monomers and the surface. In this talk we report molecular dynamics simulation where we vary the strength with which polymers are adsorbed to the surface of a small tube. Our results show that the optimal adsorption strength for the suppresion of EOF is around the phase transition for adsorption of the polymer. In the case of very strongly adsorbed polymer coatings, the coating can actually increase the EOF by thickening the debye layer since it reduces the effective radius of the capillary. Simulation results also show that at very high electric fields the adsorbed polymer layer is deformed reducing the effectiveness of the coating through a reduction in the height of the adsorbed polymer layer. Finally it is shown that very short chains make for ineffective coatings since they are not long enough to loop from the wall into the bulk of the fluid.