Electro-elastic migration of particles in viscoelastic fluid flows

Abstract

Microfluidic manipulation of particles usually relies on their cross-stream migration. A center- or wall-directed motion has been reported for particles leading or lagging the Poiseuille flow of viscoelastic polyethylene oxide (PEO) solution via positive or negative electrophoresis. Such electro-elastic migration is exactly opposite to the electro-inertial migration of particles in a Newtonian fluid flow. We demonstrate here through the top- and side-view imaging that the leading and lagging particles in the electro-hydrodynamic flow of PEO solution migrate toward the centerline and corners of a rectangular microchannel, respectively. Each of these electro-elastic particle migrations is reduced in the PEO solution with shorter polymers though neither of them exhibits a strong dependence on the particle size. Both phenomena can be reasonably explained by the theory in terms of the ratios of the forces involved in the process. Decreasing the PEO concentration causes the particle migration to shift from the viscoelastic mode to the Newtonian mode, for which the magnitude of the imposed electric field is found to play an important role.

Elasto-inertial instabilities in the merging flow of viscoelastic fluids

“…It also points to the significance of polymer entanglement in the merging flow of viscoelastic fluids, which may share a similar origin to the recent observations of c / c * dependent electro-elastic migration of particles in PEO solutions. 66,67…”

“…It also points to the significance of polymer entanglement in the merging flow of viscoelastic fluids, which may share a similar origin to the recent observations of c/c* dependent electro-elastic migration of particles in PEO solutions. 66,67 We also note that the iso-El line in Fig. 5 for the negligibly elastic domain is two orders of magnitude smaller than the value, El E 0.3, identified between the steady vortical flow in PVP (10 000 ppm/0.36 MDa, El = 0.16) & HA (1000 ppm/0.357 MDa, El = 0.010) solutions and the unsteady flow in PEO (1000 ppm/2 MDa, El = 0.37) & PAA (200 ppm/18 MDa, El = 27) solutions in our recent study.…”

Particle Size-Dependent Electrophoresis in Polymer Solutions

“…In other words, our prepared PEO solutions are all in the dilute to semidilute regime with a negligible to weak shear thinning effect . Their zero-shear-rate viscosities, η 0 , are extracted from our previous papers. , Their relaxation times were estimated from the scaling formula, λ ∝ M w 2.073 c 0.65 , using the experimentally measured λ = 1.5 ms for c = 1000 ppm and M w = 2 MDa PEO solution Table summarizes the rheological properties of our prepared PEO solutions.…”

“…The studies reviewed above are all concerned with particle electrophoresis in Newtonian fluids. Recent investigations have highlighted the significant impacts of fluid rheological properties on various electrokinetic phenomena. − In particular, a couple of theoretical papers predict the onset of particle size-dependent electrophoresis in non-Newtonian fluids even under the thin-Debye-layer limit. Khair et al developed a general framework to calculate the electrophoretic velocity of a uniformly charged colloidal particle immersed in a complex fluid with a shear-rate-dependent viscosity.…”