Deformation and organization of droplet-encapsulated soft beads

TL;DR

This paper presents an experimental method to encapsulate soft beads within droplets, manipulate their deformation and organization using microfluidics, and analyze the effects of capillary and elastic forces on their arrangement.

Contribution

It introduces a novel microfluidic technique for controlled co-encapsulation and organization of soft beads, revealing how elastocapillary forces influence their deformation and assembly.

Findings

Contact surface scales with elastocapillary number as $E_c^{1/3}$

Deformation increases with softness or smaller particle size

Beads form stable linear or 3D aggregates within droplets

Abstract

Many biological, culinary, and engineering processes lead to the co-encapsulation of several soft particles within a liquid interface. In these situations the particles are bound together by the capillary forces that deform them and influence their biological or rheological properties. Here we introduce an experimental approach to encapsulate a controlled number of soft beads within aqueous droplets in oil. These droplet-encapsulated gels are manipulated in a deformable microfluidic device to merge them and modify the liquid fraction. In the dry limit the contact surface between the hydrogels is found to be determined by the elastocapillary number $E_c$, with the contact radius scaling as $E_c^{1/3}$, indicating that the deformation increases for soft or small particles. When multiple beads are co-encapsulated within a single droplet they can be arranged into linear or three-dimensional aggregates that remain at a local energy minimum.