Cooperative Motion of Particles Drives Discontinuous Shear Thickening*

Dense suspensions of fine particles are significant in numerous biological, industrial, and natural phenomena. They are often out-of-equilibrium and display a wide array of rheological features, of which the liquid–solid phase transition under external deformation is arguably the most interesting. Over the last years, research activity at the intersection of fluid mechanics, granular materials, driven disordered systems, and soft condensed matter physics has led to a consensus that the formation of mesoscale stress-activated frictional networks drives these mechanisms. Particle simulations that led to this concept have been successful in quantitatively reproducing the non-Newtonian behavior of thickening suspensions. This talk will present three different mesoscale studies that collectively demonstrate that the cooperative motion of particles is crucial for the underlying rigidity and liquid-solid transition. First, we use the pebble game for rigid-cluster decomposition and analyze small order loops to establish a deep connection between network structure and rheology. Additionally, we use the non-affine velocity correlation length scale to build up a scaling relation connecting shear-induced diffusion and viscosity similar to the Stokes-Einstein relation in the dense limit. Finally, as friction constrains the translational motion of particles, we find pronounced frustrated rotational motion as the suspension shear thickens. These results collectively show the connection between the collective motion of particles and rheology and pave the way for creating models that go beyond the current mean-field understanding and further point towards a unified physics in particulate systems across dense suspensions and granular materials.