Electrohydrodynamics of compound liquid thread formation in a flow-focusing microchannel under an electric field.

This article focuses on the numerical investigation of the electrohydrodynamics of compound liquid thread formation under an electric field in a flow-focusing microchannel, using a phase-field method coupled with a dielectric model. It identifies two groups of flow regimes—thread formation (dripping–threading, jetting–threading, threading–threading) and non-thread formation (dripping–dripping, dripping–jetting, jetting–jetting)—and provides a regime diagram illustrating transitions influenced by electric capillary number (Cae) and hydrodynamic capillary numbers of the outer (Cao) and middle (Cam) phases. The study clarifies how electric forces interact with interfacial tension and viscous forces to stabilize or destabilize the compound liquid jets, affecting droplet size, breakup location, and thread morphology, with higher electric forces promoting elongation and stability of threads. Additionally, two scaling laws are developed to predict inner droplet radius and outer thread thickness in the dripping–threading regime, achieving prediction accuracy within ±18%, which supports the controlled fabrication of peapod-like microfibers for functional applications.