ABSTRACT
Numerous biological particles are flexible and dramatically deform in microfluidics, which offers a potential approach to interrogate the structural properties of biological particles for disease diagnosis. In this chapter, the shear-and electrokinetics-induced deformations of hyperelastic particles confined in a slit microchannel are numerically investigated using COMSOL Multiphysics® 3.5a. In a shear-driven flow, the circular particle initially located at the centerline of the channel is deformed as a perfect ellipse when the inertial effect is negligible. Under a direct current (DC) electric field directed from right to left, a negatively charged rod-like particle deforms as a C shape as it electrophoretically moves from left to right when it is initially perpendicular to the applied electric field. The shear force due to the nonuniform Smoluchowski slip velocity on the particle surface is responsible for particle deformation. In addition, the dielectrophoretic (DEP) effect could enhance the deformation as the electric field around the particle becomes asymmetric with respect to the center of the particle. When the particle is not perpendicular to the electric field imposed, a net torque stemming from the DEP effect rotates and aligns the particle with its longest axis parallel to the applied electric field, which is in qualitative agreement with the experimental observation presented in Chapter 4. As the nonuniformity of the electric field around the particle becomes weaker when the particle is aligned, the deformation is accordingly released. The numerical predictions conclude that the DEP effect is of great importance and must be considered in the modeling of electrokinetic motion of a deformable particle in microfluidics.
