Title: A new state transition in the rheology of dense suspensions

Author (Poster): Rijan Maharjan, Yale University

Abstract:

Dense suspensions of hard particles are known to have an effective viscosity that diverges as the packing fraction approaches the liquid-solid transition, $\phi_j$. This is typically measured based on energy dissipation in a steady state shear flow. In a Newtonian fluid, the same viscosity value also determines how long it takes for a flow to relax to steady state after a change in control. By performing transient flow measurements in a rheometer, we find the relaxation viscosity of suspensions start to deviate from the steady state viscosity as the packing fraction increases above $\phi_c<\phi_j$ and goes to zero at $\phi_j$. Further, we find the ratio of the normal stress to shear stress reaches a plateau $\sim$ 1 for $\phi>\phi_c$. By quantitatively identifying the critical $\phi$ for different state transitions, we show that the observed transition differs from continuous to discontinuous shear thickening, or the transition from negative to positive normal stresses, or from viscous to inertial transition. This identifies a new state transition.