Dynamics of polydisperse multiple emulsions in microfluidic channels

TL;DR

This study uses lattice Boltzmann simulations to explore how polydispersity, initial conditions, and area fraction influence the complex dynamics of double emulsions in microfluidic channels, revealing various steady states and the importance of capsule shape changes.

Contribution

It introduces a detailed simulation analysis of polydisperse double emulsions in microfluidic flows, highlighting factors affecting their nonequilibrium steady states and dynamic behaviors.

Findings

Inner drops exhibit periodic rotation or form nonmotile configurations depending on polydispersity.

Higher area fractions lead to tight contact and unidirectional movement of drops.

Capsule shape changes influence the formation of motile and nonmotile steady states.

Abstract

Multiple emulsions are a class of soft fluid in which small drops are immersed within a larger one and stabilized over long periods of time by a surfactant. We recently showed that, if a monodisperse multiple emulsion is subject to a pressure-driven flow, a wide variety of nonequilibrium steady states emerges at late times, whose dynamics relies on a complex interplay between hydrodynamic interactions and multibody collisions among internal drops. In this work, we use lattice Boltzmann simulations to study the dynamics of polydisperse double emulsions driven by a Poiseuille flow within a microfluidic channel. Our results show that their behavior is critically affected by multiple factors, such as initial position, polydispersity index, and area fraction occupied within the emulsion. While at low area fraction inner drops may exhibit either a periodic rotational motion (at low polydispersity) or arrange into nonmotile configurations (at high polydispersity) located far from each other, at larger values of area fraction they remain in tight contact and move unidirectionally. This decisively conditions their close-range dynamics, quantitatively assessed through a time-efficiency-like factor. Simulations also unveil the key role played by the capsule, whose shape changes can favor the formation of a selected number of nonequilibrium states in which both motile and nonmotile configurations are found.