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The electrophoretic velocity of a charged dielectric particle is independent of its size and shape in a Newtonian fluid under the thin Debye layer limit in the weak-field regime. Our previous paper (Bentor and Xuan, Analytical Chemistry 2024, 96, 3186-3191) reported particle size-dependent electrophoresis in viscoelastic poly(ethylene oxide) (PEO) solutions. We demonstrate herein that the fluid elasticity also induces the particle shape-dependence of electrophoretic velocity likely because the polymer stress around a particle varies with its shape. Specifically, altering the shape of a particle from sphere to pear and peanut enhances the electrophoretic velocity in a viscoelastic fluid as the particle becomes slenderer. This phenomenon, which is found absent from a Newtonian fluid, becomes stronger in higher-concentration PEO solutions because of the enhanced fluid elasticity effect. It may be utilized for the label-free electrophoretic separation of particles and cells in non-Newtonian microfluidic devices.
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Electro-elastic migration of particles in viscoelastic fluid flows
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.
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- PAR ID:
- 10500305
- Publisher / Repository:
- American Institute Physics
- Date Published:
- Journal Name:
- Physics of Fluids
- Volume:
- 35
- Issue:
- 9
- ISSN:
- 1070-6631
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1063/5.0167571
