Deformation and Organization of Droplet-Encapsulated Soft Beads

Many biological, culinary, and engineering processes lead to the coencapsulation 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 following a E_{c}^{1/3} dependence, indicating that the deformation increases for soft or small particles. When multiple beads are coencapsulated within a single droplet they can be arranged into linear or three-dimensional aggregates that remain at a local energy minimum.