Boundary effect on electrophoresis in a Carreau fluid: Simulated biocolloids at an arbitrary position in a charged spherical cavity

An unexpected particle oscillation for electrophoresis in viscoelastic fluids through a microchannel constriction

Electrophoresis plays an important role in many applications, which, however, has so far been extensively studied in Newtonian fluids only. This work presents the first experimental investigation of particle electrophoresis in viscoelastic polyethylene oxide (PEO) solutions through a microchannel constriction under pure DC electric fields. An oscillatory particle motion is observed in the constriction region, which is distinctly different from the particle behavior in a polymer-free Newtonian fluid. This stream-wise particle oscillation continues until a sufficient number of particles form a chain to pass through the constriction completely. It is speculated that such an unexpected particle oscillating phenomenon is a consequence of the competition between electrokinetic force and viscoelastic force induced in the constriction. The electric field magnitude, particle size, and PEO concentration are all found to positively affect this viscoelasticity-related particle oscillation due to their respective influences on the two forces.

Electrokinetic behavior of a pH-regulated, zwitterionic nanocylinder in a cylindrical nanopore filled with multiple ionic species

Recent advances in fabrication techniques make nano-sized pores as promising platforms for both detection and sequencing of individual biopolymers such as DNA. To simulate the electrokinetic behavior of a particle in this case, we consider the electrophoresis of a soft nanocylinder comprising a rigid core and a pH-regulated, zwitterionic polyelectrolyte layer along the axis of a rigid cylindrical nanopore. Extending the conventional electrophoresis analysis, where the liquid phase contains only one kind each of cations and anions, we assume that it contains multiple ionic species, as is usually the case in practice. The key parameters are examined for their influences on the electrokinetic behavior of a particle. These include pH, the thickness of the polyelectrolyte layer and the density of its functional groups, and the pore size. The results gathered provide necessary information for the design of an electrokinetic apparatus.

Coupling electrokinetics and rheology: Electrophoresis in non-Newtonian fluids

We present a theoretical scheme to calculate the electrophoretic motion of charged colloidal particles immersed in complex (non-Newtonian) fluids possessing shear-rate-dependent viscosities. We demonstrate that this non-Newtonian rheology leads to an explicit shape and size dependence of the electrophoretic velocity of a uniformly charged particle in the thin-Debye-layer regime, in contrast to electrophoresis in Newtonian fluids. This dependence is caused by non-Newtonian stresses in the bulk (electroneutral) fluid outside the Debye layer, whose magnitude is naturally characterized in an electrophoretic Deborah number.