Novel non-equilibrium steady states in multiple emulsions

TL;DR

This study numerically explores the complex non-equilibrium steady states in multiple emulsions under shear flow, revealing novel droplet dynamics and shape deformations influenced by shear rate and droplet count.

Contribution

It introduces new non-equilibrium steady states in multiple emulsions and analyzes their dependence on shear rate and droplet number, providing insights into their dynamic behavior.

Findings

Double emulsions reach static elliptical steady states under shear.

Encapsulated droplets exhibit planetary-like motion at low/moderate shear rates.

Shape and stress features partially captured by deformation parameters.

Abstract

We numerically investigate the rheological response of a non-coalescing multiple emulsion under a symmetric shear flow. We find that the dynamics significantly depends on the magnitude of the shear rate and on the number of the encapsulated droplets, two key parameters whose control is fundamental to accurately select the resulting non-equilibrium steady states. The double emulsion, for instance, attains a static steady state in which the external droplet stretches under flow and achieves an elliptical shape (closely resembling the one observed in a sheared isolated fluid droplet), while the internal one remains essentially unaffected. Novel non-equilibrium steady states arise in a multiple emulsion. Under a low/moderate shear rates, for instance, the encapsulated droplets display a non-trivial planetary-like motion that considerably affects the shape of the external droplet. Some features of this dynamic behavior are partially captured by the Taylor deformation parameter and the stress tensor. Besides a theoretical interest on its own, our results can potentially stimulate further experiments, as most of the predictions could be tested in the lab by monitoring droplets shapes and position over time.