Search for: All records

The stability of a rigid particle in yield stress fluids, comprised of soft particle glasses (SPGs), is investigated in shear flow under an applied external force, such as weight, using particle dynamics simulations. Results provide the critical force threshold, in terms of the dynamic yield stress and the flow strength, required to initiate sedimentation of the rigid particle over a wide range of shear rates and volume fractions. The streamlines of the SPGs show local disturbances when the rigid particle settles. The form of these disturbances is consistent with the microdynamics and microstructure response of the neighboring soft particles of the sedimenting rigid particle. Sedimenting particle induces non-affine displacement to the suspensions at low shear rates and high applied forces, while these dynamical events are localized and suppressed at high shear rates. Stability diagrams, which provide the conditions of the sedimentation of the rigid particle, are presented in terms of the applied force and the shear rate. These individual stability diagrams at each volume fraction map onto a universal stability diagram when the external force is scaled by the dynamic yield stress and shear rate with a ratio of the solvent viscosity to the low-frequency modulus of the SPGs. 

Particle dynamics simulations are used to determine the shear-induced microstructure and rheology of jammed suspensions of soft particles. These suspensions, known as soft particle glasses (SPGs), have an amorphous structure at rest but transform into ordered phases in strong shear flow when the particle size distribution is relatively monodisperse. Here, a series of bidisperse SPGs with different particle radii and number density ratios are considered, and their shear-induced phase diagrams are correlated with the macroscopic rheology at different shear rates and volume fractions. These shear-induced phase diagrams reveal that a combination of these parameters can lead to the emergence of various microstructures such as amorphous, layered, crystals, and in some cases, coexistence of amorphous and ordered phases. The evolution of the shear stress is correlated with the change in the microstructure and is a shear-activated process. Stress shows pseudo-steady behavior during an induction period before the final microstructural change leading to the formation of ordered structures. The outcomes provide a promising method to control the phase behavior of soft suspensions and build new self-assembled microstructures.