(586j) A Simple Trick of the Light: Direct Imaging of Single Droplets in Dense Emulsions

Dense emulsions have many important industrial applications, but compared to dilute emulsions our fundamental understanding of droplet deformation and breakup is still developing. This is largely due to limitations from light scattering; a refractive index contrast between the dispersed and continuous phases prevents direct imaging of individual droplets in bulk flow conditions. To address this challenge, we have formulated index-matched dense emulsions with viscosity-matched "contrast" droplets that allow direct visualization of individual droplets under ordinary brightfield microscopy. Using 3D printed millifluidic devices, we have observed complex and interesting flow behaviors including asymmetric deformations, droplet breakup, and potential evidence of size-based segregation. Quantitative analysis is ongoing, but preliminary results include a number of visually striking videos that hint at promising new directions for future research.