Nonlinear Rheology of Dense Non-Brownian Suspensions: What is the role of particle shape?

Suspensions of non-Brownian particles in viscous fluids are relevant in engineered processes and in natural phenomena. These suspensions typically consist of solid particles of

nonspherical shape and often exhibit nonlinear behavior such as shear thinning and/or shear thickening even when the suspending fluid is Newtonian. This talk focuses on such nonlinear rheological behaviors and it is motivated by one central question: ``What is the role of particle shape?". We will present our recent results concerning the rheology of two suspensions, which differ solely through the particle shapes. One suspension was made of spheres, and the other of globular facetted particles produced by crushing identical spheres. The suspension of crushed particles exhibited a higher viscosity than the suspension of spheres for the same volume fraction and applied stress and displayed a steeper shear thinning behavior. The results show that the stronger nonlinear rheology of crushed particles stems from a combination of stress-weakening sliding friction and extra resistance to rolling motion due to the angular shape of the crushed particles. We will use these recent findings to put forward a scaling analysis to systematically explore the nonlinear rheology of dense non-Brownian suspensions made of nonspherical particles of arbitrary shape with the interplay of shape with hydrodynamic, colloidal, and contact forces.