Role of flow-induced dynamical heterogeneities in macroscopic rheology of soft particle glasses

Soft particle glasses (SPG), which are jammed beyond the random close-packing fraction of equivalent hard spheres, show rich rheology under shear flow. The softness of particles allows them to compress to volume fractions larger than the random close-packing and form flat facets at the contact between particles. In this regime, the thermal energy contribution becomes minor, and the contact forces are the dominant source of dynamics and govern the morphology and macroscopic rheology. These fluids demonstrate yield stress behavior and flow according to the Herschel-Bulkley (HB) relationship. In our study, we have used our particle dynamics numerical method to establish a relation between the various factors that affect the microscopic dynamics and rheology of these flow-induced SPG systems; some of these factors being the volume fraction of the particles, nature of the solvent and the strength of the flow. The analysis of the shear flow curves and the trajectories of particles have shown strong evidence of dynamical heterogeneities in the system. The length scale of the domains of these heterogeneous motions is linked to the stress-strain behavior at low and high shear rates. Furthermore, the study of the non-affine square displacement shows the presence of avalanches in the dynamics of the system. These results establish a direct relationship between the microscopic dynamics of SPGs and their macroscopic properties that can be utilized in designing yield stress fluids.