Microstructure, microscopic dynamics, and rheology of jammed soft particles with attractive interactions

We use 3D particle dynamics simulations to investigate the microstructure, particle-scale dynamics, and macroscopic rheology of jammed suspensions of soft and deformable particles. This multiscale study is carried out in the framework of a micromechanical model that considers that particles move and rearrange under the combined action of Hertzian repulsive forces, short-range attractive forces, and elastohydrodynamic lubrication forces. Attractive interactions strongly modify the microstructure prevailing in purely repulsive situations: the pair distribution functions exhibit two alternating anisotropic repulsion- and attraction-induced shells, the overall compression increases, and contacts are fewer but larger. They induce a specific flow instability characterized by spatiotemporal fluctuations. After averaging, the shear stress as well as the first and second normal stress differences of attractive suspensions can be mapped onto the behavior of repulsive suspensions, when stresses and shear rate are nondimensionalized by the dynamic yield stress and the duration of the rearrangements, respectively. These results reveal a subtle interplay between hydrodynamic and attractive forces. Attractive forces are dominant at low shear rates and close to the jamming transition, whereas hydrodynamic forces control the rheology at high shear rates and far from jamming.