Simulation model of concentrated colloidal nanoparticulate flows.

This paper presents a simulation model of concentrated colloidal nanoparticulate flows to investigate self-organization of the nanoparticles and rheology of the colloid. The motion of solid nanoparticles is treated by an off-lattice Newtonian dynamics. The flow of solvent is treated by an on-lattice fluctuating Navier-Stokes equation. A fictitious domain method is employed to couple the motion of nanoparticles with the flow of solvent. The surface of nanoparticles is expressed by discontinuous solid-liquid boundary to calculate accurately contact interaction and Derjaguin-Landau-Verwey-Overbeek interaction between the nanoparticles. At the same time, the surface is expressed by continuous solid-liquid boundary to calculate efficiently hydrodynamic interaction between the nanoparticles and the solvent. Unlike other simulation models that focus on the hydrodynamic interaction, the present model includes all crucial interactions, such as contact force and torque, van der Waals force, electrostatic force, hydrodynamic force, and torque including thermal fluctuation of the solvent that causes translational and rotational Brownian motions of the nanoparticles. Especially the present model contains the frictional force that plays a significant role on nanoparticles in contact with one another. A fascinating novelty of the present model is that computational cost is constant regardless of the concentration of nanoparticles. The capability of the present simulation model is demonstrated by two-dimensional simulations of concentrated colloidal nanoparticles in simple shear flows between flat plates. The self-organization of concentrated colloidal nanoparticles and the viscosity of colloid are investigated in a wide range of Péclet numbers.