(334e) Rheological Behavior of Soft Particle Glasses during Start-up Flow: Insights from Experiments and Simulations

Soft particle glasses (SPG), which are jammed beyond the random close-packing fraction of equivalent hard spheres, show rich rheology under shear flow. The startup flow of these suspensions is studied using three-dimensional particle-dynamics simulations and experiments at different particle packing fractions and shear rates. Experimental data show that the shear stress undergoes an overshoot after a linear elastic response, and then it attains a steady-state value as a function of the shear strain. The value of the strain at which the stress overshoot occurs is close to 0.1, and it slightly increases with the shear rate. Furthermore, the rheological experiments demonstrate that the magnitude of the stress overshoot increases with the aging of the suspensions. Simulations are used to characterize the effect of aging and applied shear rate on the stress overshoot and rationalize the experimental observations. Results show that the overshoot occurs in both shear stress and elastic energy of the system as a function strain. There is a substantial microstructural change before the overshoot, in which particles significantly accumulate on the axis of compression of the test particle. Simulations are also used to understand the microscopic origin of the stress overshoot in the aged suspensions. Finally, a simple equation that combines linear elastic response with a power-law decay is used to characterize transient results of shear stress in both experiments and simulations.