(519b) Hydrodynamic Simulations of Constant Stress and Pressure Rheology of Dense Colloidal Suspensions

Wang, M., California Institute of Technology
Brady, J. F., California Institute of Technology
We study the constant stress and pressure rheology of polydisperse colloidal suspensions with volume fractions up to the jamming density via a new implementation of Stokesian dynamics, the Spectral Ewald Accelerated Stokesian Dynamics (SEASD). The non-Brownian limit of the simulations agrees quantitatively with the experiments of Boyer et al. [Phys. Rev. Lett. 107, 188301 (2011)] with only a shift in the maximum volume fraction. Consistent with non-hydrodynamic simulations, the suspension shear viscosity diverges algebraically with the distance from the arrest volume fraction along constant pressure contours. The low volume fraction continuous shear thickening observed at constant volume fraction no longer occurs at fixed pressure. Structurally, in the high imposed pressure limit, the suspensions develop string-like ordered structures that disappear with further stress increase. Using a Péclet number based on the long-time self-diffusivity, we discover a universal collapse of the interaction contribution of the friction coefficient, suggesting that a non-equilibrium Stokes-Einstein-Sutherland relation for the long-time self-diffusivity and the suspension shear viscosity holds with an effective temperature proportional to the suspension osmotic pressure for all imposed stresses and pressures. With the same Péclet number, the structural signature of the suspensions also collapses to a master curve. That similar collapses are also found in non-hydrodynamic simulations suggests that the hydrodynamic interactions only quantitatively affect the behavior of dense suspensions near flow-arrest transitions.