Systems on the verge of jamming are able to flow and relax due to the cooperative motion of particles, molecules, bubbles, grains, etc. in changing neighbors.  The rearrangement dynamics is now accepted to be heterogeneous, with some groups of neighbors remaining intact while other groups become mobile and change neighbors.  In this talk I will discuss experiments on such dynamical heterogeneity three different granular systems. This includes air-fluidized beads, where there is an effective temperature with real statistical mechanical meaning and jamming is approached by density and airspeed; granular heap flow, where jamming is approached by depth from the free surface; and dense suspensions of soft colloidal NIPA beads, where jamming is approached by both density and shear rate.  Emphasis will be given to how four-point susceptibilities may be measured and interpreted in terms of the number of particles in the fast-rearranging regions.  We are finding a consistent picture for all three experimental systems, where this number grows on approach to jamming as the 1/3 power of a dimensionless relaxation time.

Growth of dynamical heterogeneity in dense granular materials on approach to jamming

244th National Meeting (2012)

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