Molecular dynamics simulations of polymeric fluids in narrow channels: methods to enhance mixing

Mixing of shear thinning polymeric fluids in long channels with patterned boundary conditions is studied through molecular dynamics simulations. Patterned wettability was shown to induce spatially varying slip lengths at the channel walls which in turn induce mixing in the fluid. To quantify the amount of mixing for different wave lengths of patterns, transverse velocity profiles were evaluated. The transverse velocity profiles from the molecular dynamics simulations were then compared with predictions from continuum modeling and good quantitative agreement was found. Offsetting the pattern was shown to produce better mixing in the center of the channel. Transverse flow is found to increase when the radius of gyration of the chains is smaller than the pattern length. We also implement an oscillating (time dependent) body force and find that the transverse flow increases significantly. However, we do not find an increase in transverse flow with frequency of the oscillation as predicted from continuum modeling and we postulate reasons for this behavior.