(337d) Structural Correlation and the Flow Mechanism of Near-Jamming Suspensions

The divergence of the viscosity at the jamming fraction in suspensions is well-known, and the normal stress response functions behave similarly. In connection with recent understanding of very strong shear-thickening, the jamming fraction is found to be stress-dependent in suspensions which exhibit a lubricated-to-frictional rheology with the characteristic stress for the transition determined by a repulsive interparticle force. As a result, jamming – i.e, going from flowing to non-flowing – can be examined for a single material by increasing the stress. In this work, the behavior of the suspension flow mechanism on approach to jamming will be studied by variation of the shear stress or the solid fraction, using the lubrication flow-DEM (LF-DEM) simulation method. The “flow mechanism” here implies the development of particle structures due to the imposed stress and the manner in which they move as they approach a state of global rigidity at the jammed state. This is found to occur through nearly rigid-body motions of clusters of particles. Through statistical analysis of the motion correlations in shear flow, we find that the bulk shear flow becomes progressively obscured by fluctuating rotations and translations of these clusters on approach to jamming. A consequence is that the fluctuations become predominant over the mean flow, thus resulting in progressively larger dissipation rate for a given strain rate as jamming is approached, thus providing a mechanistic basis for the viscosity divergence. Various aspects of this scenario, including the lifetime of identifiable clusters and the location of the most rapidly rotating particles, will be developed, both quantitatively and through qualitative video demonstrations.