Microscopic Rearrangements in the Flow of Polydisperse Dense Emulsions*

We study the flow of dense polydisperse quasi-two-dimensional emulsions. In particular, we are interested in highly polydisperse samples with the largest droplets as much as ten times the size of the smallest. The droplets are confined between two parallel glass plates and driven to flow by a syringe pump. We use video microscopy to examine how rearrangements differ for large and small droplets. In particular, we find the large droplets follow the mean flow, while the small droplets move more erratically. We try to quantify these results by looking at the nearest neighbor changes and nonaffine motions.We explore different means of defining affine motion, including definitions based on nearest neighbors and definitions based on regions of space. The former varies quite a bit depending on the size of droplets, whereas the latter is simpler but lacks a sensitivity to droplet size.