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Lateral Migration of a Droplet in a Uniform Electric Field

With the advent of modern small-scale devices, the use of external electric field to manipulate particle, droplet and biological cells in a suspending medium is growing day by day. In this talk, I will highlight the implications of directionality of an external uniform electric field on the droplet motion. I will provide two examples of our two works: (i) Motion of a buoyant droplet in the presence of uniform electric field. (ii) Motion of a neutrally buoyant droplet in the combined presence of Poiseuille flow and uniform electric field. First study shows that tilt angle, which quantifies the angle of inclination of the applied electric field with respect to the direction of gravity, has a significant effect on the magnitude and direction of the droplet velocity. When the electric field is tilted with respect to the direction of gravity, a non-intuitive lateral motion of the droplet is obtained in addition to the buoyancy driven sedimentation. Second study reveals that charge convection can cause a spherical non-deformable droplet to migrate in the direction normal to imposed Poiseuille flow. Depending on the orientation of the applied uniform electric field and the relevant droplet/medium electrohydrodynamic parameters, the droplet may migrate either towards the centreline of the flow or away from it. Most interestingly, the droplet can settle in an off-centreline steady state transverse position. These studies facilitate to acquire an idea about the various controlling parameters which affect the drop velocity, droplet trajectory and steady state transverse position of the droplet. Using these, we may achieve fine-tuned control over the motion and final steady transverse position of drops in droplet-based microfluidic devices.