Electrohydrodynamic deformation and oscillatory dynamics of a neutrally buoyant droplet

This study investigates the electrohydrodynamic deformation of dielectric liquid droplet exposed to a uniform electric field. Experiments are performed using a two-phase system comprising a silicone oil droplet dispersed in castor oil as the bulk. The droplet behaviors, including deformation, flattening, oscillation, and rotation, are analyzed across a range of electric field strengths using shadow imaging technique. For electric field strengths ranging from Eo = 4.5 to 5.75 kV/cm, the silicone oil droplet initially deforms into an oblate shape, with their axes tilting relative to the direction of the applied field. At lower field intensities, i.e., Eo4.75 kV/cm, the droplet deformation and tilt/orientation remain steady; however, at higher electric field strengths, the droplets display oscillatory behavior characterized by periodic tilting and deformation dynamics. The results reveal distinct regimes of droplet deformation governed by electrohydrodynamic instabilities, where the induced electric torque causes the droplet axis to deviate from the field direction before relaxing into a transiently stable configuration. This study identifies the transitions of droplet response from a monotonic deformation at low field intensity to non-monotonic oscillatory deformation behavior at higher fields, determined by the dielectric contrast and fluid properties of the two phases. These insights enhance the current understanding of droplet dynamics in electric fields and hold relevance for technologies such as inkjet printing, microfluidics, electro-coalescence, and phase separation processes.