Corrugated interfaces in multiphase core-annular flow

TL;DR

This paper investigates how inner drops in multiphase core-annular flow cause corrugated interfaces, affecting emulsion formation, especially at low interfacial tensions where traditional breakup is suppressed.

Contribution

It introduces a numerical analysis revealing the formation of corrugated interfaces due to inner drop perturbations in high Weber number flows.

Findings

Corrugated interfaces are caused by inner drop perturbations.

Flow becomes highly corrugated at low interfacial tension.

Corrugations prevent controlled double emulsion formation.

Abstract

Microfluidic devices can be used to produce highly controlled and monodisperse double or multiple emulsions. The presence of inner drops inside a jet of the middle phase introduces deformations in the jet, which leads to breakup into monodisperse double emulsions. However, the ability to generate double emulsions can be compromised when the interfacial tension between the middle and outer phases is low, leading to flow with high capillary and Weber numbers. In this case, the interface between the fluids is initially deformed by the inner drops but the jet does not break into drops. Instead, the jet becomes highly corrugated, which prevents formation of controlled double emulsions. We show using numerical calculations that the corrugations are caused by the inner drops perturbing the interface and the perturbations are then advected by the flow into complex shapes.