Cross stream chain migration in nanofluidic channels: Effects of chainlength, channel height, and chain concentration

摘要

We use molecular dynamics simulations to study the shear flow of a polymer solution in ananochannel by using an explicit, atomistic model of the solvent. The length scales representing thechain size, channel size, and the molecular scale structure in these nanochannels are comparable.The diffusion and hydrodynamic interactions in the system are governed by the intermolecularinteractions in the explicit solvent model that is used in the simulations. We study the cross streammigration of flexible polymer chains in a solution that is subjected to a planar Couette flow in ananochannel. We present a detailed study of the effects of chain length, channel size, and solutionconcentration on the cross stream chain migration process. Our results show that when a dilutesolution containing a longer and a shorter chain is subjected to shear flow, the longer chains that arestretched by the flow migrate away from the channel walls, while the shorter chains that do notstretch also do not exhibit this migration behavior. The thickness of the chain depletion layer at thechannel surface resulting from cross stream migration is found to increase with an increase in thechannel height. On the other hand, this degree of migration away from the channel walls is foundto decrease with an increase in the solution concentration. In solutions with concentrationscomparable to or greater than the overlap concentration, the depletion layer thickness in shear flowis found to be comparable or slightly smaller than that observed in the absence of flow.