Flow-induced migration of polymers in dilute solution

Abstract

We investigate the lateral migration of a confined polymer under pressure driven and uniform shear flows. We employ a hybrid algorithm which couples point particles to a fluctuating lattice-Boltzmann fluid. We observe migration in both uniform shear and pressure driven flows, supporting the idea that migration is driven by a combination of shear and hydrodynamic interactions with the wall, rather than by the shear gradient. Recent numerical and theoretical investigations have suggested that polymers migrate toward the centerline when hydrodynamic interactions are included, but our simulations show that in sufficiently narrow channels there is a reversal of direction and the polymers move toward the wall.

Pressure driven flow of polymer solutions in nanoscale slit pores

“…Theories have therefore been based on simplified systems rather than on polymer solutions. Previous theoretical and com-putational studies that focused on the density profiles of polymers in uniform shear flow (i.e., Couette flow) or pressure driven flow (i.e., Poiseuille flow) have been conflicting [9,10,12,13,14]. Previous Brownian dynamics simulations showed a migration of the polymer chains towards the wall [9,10].…”

“…This result contrasts that of Jendrejack et al [11], where even in the strong confinement regime, a migration away from the wall is observed. In the presence of uniform shear flow, Usta et al [14] observed that the density profile does not exhibit a peak in the mid-section of the slit, instead of a dip. The presence of a dip in the mid-section of the slit must therefore be associated with gradients in the shear rate, present in pressure driven flow.…”

“…The depletion from the wall becomes substantial for large flow rates. In the more recent simulations by Usta et al [13,14], which are based on a bead model for the polymer chains coupled to a lattice Boltzmann description for the solvent, the polymer density profile was also found to exhibit a minimum in the center-plane of the slit followed by two symmetric maxima. Near the wall, a migration away from the wall is observed when the ratio between the thickness of the slit and the equilibrium radius of gyration of the polymer chains is large, i.e., in the weak confinement regime.…”

“…For example, the understanding of the structure and dynamics of polymeric molecules in micro-channels is important to DNA sequencing in channels with widths ranging from 10 to 50µm [2], DNA delivery through micro-capillaries in gene therapy, and to lab-on-chip applications that involve polymers [3]. Issues of particular interest pertinent to polymer solutions in the presence of laminar flow is the mass distribution of polymers across the channel, the polymers conformational distribution, and the effect of the polymer chains on the profile of the solution velocity field [1,2,4,5,6,7,8,9,10,11,12,13,14,15].…”

Dynamics of fibers in a wide microchannel

“…It is accepted that confinement has a crucial impact on the behavior of single polymers [17,20] by effects of spatially varying shear rate and hydrodynamic interactions with the impenetrable walls. In general, the flow properties of flexible fibers have been shown to be highly influenced by hydrodynamic interaction, both within the fiber and with the system boundaries [21].…”