Combined polarization and electrophoretic influence on bubble dynamics in leaky dielectric fluids

Abstract

Electrohydrodynamics (EHD) is a powerful tool for manipulating fluid interfaces. While many studies focus on polarization forces in ideal dielectrics, the behavior of modern leaky dielectric fluids, where free charges and Coulomb forces are significant, remains less understood. This study investigates the dynamics of air bubbles in HFE-7100, a representative leaky dielectric fluid, under DC, polarity-changing, and high-frequency (1 kHz) AC electric fields. High-speed imaging reveals that when the charge relaxation time (${\tau }_e$) is comparable to the bubble lifespan, complex dynamics emerge. Under DC fields, this leads to significant discrepancies in bubble lifespans and waiting times. During polarity reversal, Coulomb forces temporarily counteract buoyancy, pinning bubbles to the surface and creating unique triangular shapes. Conversely, high-frequency AC fields suppress these charge effects, leading to highly consistent, polarization-dominated dynamics, albeit with prolonged surface residence times. These findings demonstrate that free charges are critical in EHD phenomena in leaky dielectric fluids and highlight the limitations of quasi-electrostatic models. This work provides a foundation for refining theoretical models for EHD applications with modern fluids.