Sediment formation by Brownian dynamics simulation: Effect of colloidal and hydrodynamic interactions on the sediment structure

Abstract

The formation of a gel‐like sediment by a process of irreversible single‐particle accretion has been simulated in three dimensions by the computational technique of Brownian dynamics. The model incorporates hydrodynamic interactions between spherical particles at the level of the Rotne–Prager approximation, and colloidal interactions are described in terms of the Derjaguin–Landau–Verwey–Overbeek (DLVO) pair potential of mean force for electrostatically stabilized particles. The density and structure of simulated sediments have been determined as a function of ionic strength and sedimenting field strength. Depending on the conditions, sediment volume fractions range from 0.09 to 0.33. Colloidal forces can significantly affect the short‐range structure of low‐density diffusion‐controlled sediments. Sediment density increases strongly with increasing field strength, and sediment structures as measured by the particle pair distribution function become more liquid‐like as the volume fraction increases. Hydrodynamic interactions have little effect on aggregate structure at low field strengths where Brownian aggregation is dominant, but the presence of hydrodynamic interactions is essential for the formation of high‐density sediments at high field strengths. This work suggests that, in general, colloidal forces and hydrodynamic interactions cannot be neglected in simulations of colloidal aggregration and gelation.