Microscopic stabilization mechanism of droplet in the coupling of electric and rotating flow fields

Abstract

Electrohydrodynamic manipulation of oil–water interfaces is a promising route for intensified separation and emulsion control, yet a molecular-level picture of how coupled electric and rotating flow fields (RF) dictate droplet stability is still lacking. In this paper, molecular dynamic (MD) simulations are performed to elucidate the droplet polarization, deformation, breakup and stability under direct current (DC) field, alternating current (AC) field, pulsed electric field (PEF) and rotating electric field (RE), respectively, acting simultaneously with a RF field. The results show that (i) the nature of the electric field dominates the breakup threshold: DC fields stretch droplets continuously and give the lowest critical electrocapillary number (Ca_E), whereas the periodic reversal of AC fields favor rapid retraction and afford the highest stability; overall stability follows the order of AC field > RE field > PEF field > DC field. (ii) Coupling electric and centrifugal forces significantly amplifies droplet deformation; an appropriate angular velocity, however, suppresses breakup and enlarges the droplet stability. (iii) Dipole moment build-up and hydrogen-bond depletion are identified as molecular signatures of impending instability: DC fields induce the fastest loss of hydrogen bonding, while AC and RE fields mitigate electrostatic overstretching and preserve interfacial structure. (iv) Optimizing electric-field frequency (5–6.7 GHz for PEF) and introducing Span-80 and SiO₂ synergistic effects enhance stability, efficiently suppressing breakup even under strong fields. These findings clarify how electric and hydrodynamic forces, together with interfacial additives, synergistically manipulate droplet stability, and provide theoretical guidance for the design of high-efficiency electro-centrifugal separators.