Contour Dynamics of Dense Emulsion Droplets in Extensional Flows

We present the continued development of an experimental framework for capturing and describing droplet deformations in dense emulsions subject to bulk planar extensional flows. We circumvent the typical opacity of these materials by studying a subset of refractive index (RI) mismatched droplets in a milieu of rheologically identical RI matched droplets. These emulsions are visualized in a millifluidic cross-slot device under visible light microscopy, from which ensemble information on droplet dynamics may be extracted and related to the bulk rheological properties of the emulsion. We employ a state-of-the-art computer vision model to identify and segment the projected droplets in high-speed videos, and focus particularly on describing the dynamics of contour fluctuations arising from the flow and motion of (invisible) neighboring droplets, up to and including droplet breakup. From individual and ensemble analyses, correlations may be drawn between emulsion characteristics (i.e. volume fraction, droplet size distribution), the imposed flow (Capillary number), and droplet dynamics and breakup phenomena.