Electrohydrodynamic manipulation of droplets in confined spaces: impact of geometric eccentricities and material properties

This paper takes the advantage of the elemental enriched finite element method to provide a comprehensive analysis of the factors influencing the electrohydrodynamics of droplets confined within microspaces. Specifically, the impact of electrical property ratios (permittivity and conductivity) and eccentricities along the x- and y-axes on droplet deformation is investigated. A critical confinement size is revealed based on the findings of the paper: below this threshold, droplet deformation exhibits a transition, in contrast to the observations made in unbounded domains. Furthermore, the numerical results demonstrate a strong deformation dependence on both the electrical properties ratios and the confinement ratio itself. It is found that the deformation parameter shows a monotonic decrease as the conductivity ratio increases relative to the permittivity ratio. The study further reveals that droplet location within the domain plays a crucial role. When centered, pressure forces become relevant at high confinement ratios, primarily affecting prolate droplets, while electric forces dominate the shaping of oblate droplets. For off-center droplets (with geometric eccentricity), the pressure force becomes even more critical.