Shear-induced dynamical heterogeneities in soft particle glasses

Soft particle glasses (SPGs), which are jammed beyond the random close-packing fraction of equivalent hard spheres, show rich rheology under shear flow. These yield stress fluids show weak elastic solid response at low stresses and flow according to the Herschel-Bulkley behavior. In this work, we use our particle dynamics numerical method to unravel the interrelation between the softness, size distribution, volume fraction of the particles, and strength of the flow on the microscopic dynamics and rheology of SPGs using computational techniques. Results show that shear transformation zones in the form of domains with relatively high nonaffine displacement appear, grow, and then disappear at low shear rates close to the dynamic yield stress limit. This repeated cycle gives rise to the flow at low shear rates. On the other hand, the dynamics of the particles at high shear rates become localized, and small pockets of particles with high mobility appear and disappear periodically. We will demonstrate that there is a unique timescale set by the ratio of the solvent viscosity and shear modulus of the suspensions which controls the transition between these two limits and flow behavior in the yield stress fluids. Thus, a direct relationship between the microscopic dynamics and macroscopic rheology of SPGs will be established.