Flow-induced transition of compound droplet to composite microfiber in a channel with sudden contraction

The deformation behavior and hydrodynamic stability of a three-dimensional Newtonian single-core compound droplet during flow in a channel with sudden contraction were studied by numerical modeling. This research was motivated by the quest for conditions of the steady transition of a compound droplet into a composite microfiber, whose core is stretched as much as the shell. With this aim, the dynamics and morphology evolution of the compound droplet were analyzed in detail as functions of capillary number, core-to-shell relative viscosities, interfacial tensions, and the relative initial core radius. It was found that the effective elongation of the core occurs either with a significant increase in the shell viscosity relative to the ambient fluid or with a decrease in the core viscosity with respect to the shell. In this case, as the composite droplet advances into the narrowing zone of the canal, it continues to stretch, becoming a bullet-shaped composite microfiber. A new mechanism of disintegration of the compound droplet was revealed, which is caused by the core destabilizing effect and manifests itself either with an increase in the relative core/shell interfacial tension or the relative core viscosity.

Automated summary

The deformation and stability of a three-dimensional Newtonian single-core compound droplet during flow in a channel with sudden contraction were investigated using numerical modeling. The study aimed to identify the conditions for the steady transition of a compound droplet into a composite microfiber. The results showed that the effective elongation of the core can be achieved by either increasing the shell viscosity relative to the ambient fluid or decreasing the core viscosity relative to the shell. Additionally, a new mechanism of disintegration of the compound droplet was discovered, caused by the core destabilizing effect resulting from an increase in the relative core/shell interfacial tension or relative core viscosity.