Flow of amorphous solids modeled with emulsion droplets

We use quasi-two-dimensional emulsions as experimental models to study the flow of jammed materials (amorphous solids). Our emulsions are oil droplets in water and are compressed between two parallel glass plates so that the droplets are deformed into pancake-like disks. We use microscopy to observe these droplets as they flow. From the deformed outlines of the droplets, we can measure all of the inter-droplet forces to within 10%. In this way, we study the relationship between the local stresses in the system and the rearrangements as the sample is sheared. In particular, we find that at very slow flow rates (quasi-static flow), we see large avalanches of rearrangements, whereas at higher flow rates rearrangement events occur more frequently but involve fewer droplets. The simplest rearrangement involves four droplets (a 'T1 event') and we confirm theoretical predictions for the quadrupolar spatial pattern of the stress redistribution around the T1 events.