We use quasi-two-dimensional emulsions as experimental models to study the flow of jammed materials. 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. 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. We also study gravity-driven flow in hoppers and investigate the probability of clogging as a function of the hopper exit size. Here, experiments and simulations show that the softness of the particles is important, as soft particles form less stable arches and thus reduce the probability of clogging.
BIO Sketch | Prof. Eric Weeks earned his undergraduate degree in engineering physics at the University of Illinois at Urbana-Champaign. ("Engineering" physics meant he had to take drafting and Fortran.) In 1997 he graduated with a Ph.D. in physics from the University of Texas at Austin, working in the Center for Nonlinear Dynamics with Prof. Harry Swinney. His thesis work was on experiments studying anomalous diffusion and atmospheric phenomena. He started a postdoctoral fellowship at the University of Pennsylvania with Prof. David Weitz and Prof. Arjun Yodh, and finished his postdoctoral work at Harvard University when the Weitz lab moved there. In January 2001 he moved to Emory University, where he is currently a Dobbs Professor of Physics and also the department chair. In July 2018 he will start a new position at Emory University as the Director of the Center for Faculty Development and Excellence, where he'll work with faculty across the whole university.