| Dynamic simulations of colloidal monodisperse, bimodal and polydisperse suspensions of spherical particles subjected to shearing flow are described. Dispersed hard spherical particles suspended in a Newtonian fluid experience hydrodynamic interactions, Brownian forces, and DLVO forces; these colloidal interactions are considered in the suspension model. DLVO type force contributions include electrostatic and van der Waals forces, which are dependent on the absolute particle size. The particles experience far-field many body interactions and near-field interactions. The near-field interactions include hydrodynamic lubrication as well as electrostatic and van der Waals forces. The convergence of the far-field interactions is accelerated by means of Ewald summation, calculated for arbitrarily sized particles. Transport properties of the suspension, such as the relative viscosity, drag coefficients, and particle diffusivities are found. The simulation model is used to examine the microstructure of colloidal suspensions, and to determine the effective dynamic and time averaged viscosities of sheared suspensions. The microstructure is determined by projecting the pair distribution function onto the vorticity–velocity gradient plane. Variation in Péclet number produces a shift in the structure of monodisperse suspended particles from ordered at low Pe, to disordered at moderate Pe, to ordered at high Pe. The Péclet number is defined as the shear rate times the square of the characteristic length divided by the diffusivity of an isolated particle D0, The Stokes-Einstein diffusivity relation is D0 = kT/6πμ a where kT is the fluid thermal energy, μ is the fluid viscosity, and a is the radius of the sphere. Bimodal suspensions at the same volume fraction and Péclet number show a complete disruption of the structure seen in the monodisperse case. |
