Visualization of Droplet Dynamics in Dense Emulsions

We present a visualization scheme of transparent, refractive index (RI) matched dense oil-in-water emulsions doped with RI mismatched droplets, enabling the collection of statistical ensembles of individual droplet trajectories and deformations under flow. Dense emulsions are commonly encountered in a variety of industrial and commercial settings, yet their droplet-scale dynamics are poorly characterized due to the opacity of these materials from high interfacial areas and light scattering. Furthermore, the development of theoretical models for the generation and rheological behavior of dense emulsions requires a statistical understanding of droplet-scale dynamics, for which experimental evidence remains lacking (particularly for large, breakable droplets). We will present our results of these doped dense emulsions subjected to planar extensional flows in 3D printed millifluidic cross-slot devices across a range of droplet volume fractions and capillary numbers. Subsequently, distinguishing behaviors of concentrated systems, namely non-affine droplet motion and deformation, are characterized and related to the rheological behavior of the emulsions.