Dynamic and Structural Heterogeneity of a Jamming Emulsion System

We experimentally study the jamming behavior of a slowly compressed quasi 2-D emulsion system. Our samples are oil-in-water emulsions confined between two close-spaced parallel plates. The oil droplets are non-Brownian and deformable. In our experiment, water slowly evaporates from an open edge of the chamber and the volume fraction of oil droplets gradually increases, which results in the sample going from barely jammed to well overjammed (volume fraction approaching 1). As water evaporates, the oil droplets move cooperatively with their neighbors to fill in the voids and get closer to the others due to the lack of free space. By means of microscopy, we analyzed the motions of the oil droplets and characterized the local structural heterogeneity of the emulsions based on the radical Voronoi cells. As the emulsions get jamming, the structural heterogeneity decreases, and the cooperative motion of the oil droplets slows down. Our results show a correlation between the local structural heterogeneity and dynamic heterogeneity in this jamming emulsion system.