Influence of Electrohydrodynamic on Droplet Stability in Leaky Dielectric Media

Abstract

This work examines the deformation dynamics of dielectric liquid droplet when exposed to a uniform electric field. The experimental investigation involves two-phase configurations, here as silicone oil droplets suspended in castor oil. The droplet dynamics including deformation, elongation, oscillation, and rotation are investigated over a range of electric field strengths using shadow-imaging. In parallel, fluorescent tracer particles were employed to perform threedimensional Lagrangian Particle Tracking (3D-LPT) using the Shake-The-Box (STB) technique, allowing for a detailed characterization of the internal electrohydrodynamic flow within the droplet subjected to a uniform electric field. For silicone oil droplets in castor oil medium (S/R > 1), the droplets initially deform into oblate shape. At sufficiently high electric field strengths, the droplet undergoes an Electrohydrodynamic instability, aligning their axis at an angle to the direction of electric field due to the imbalance in induce electric torque. Upon further increasing the field strength, the droplets display oscillatory deformation before settling into a transiently stable configuration. The current study identifies and characterizes the distinct regimes of droplet behaviour, from initial deformation at low electric fields to oscillatory behaviour at high field strengths depending upon the relative dielectric and fluid properties of the liquid phases.