The application of modified Stokesian dynamics to 3D particle motion simulations of pigment coating colours

A 3-dimensional particle dynamics simulation technique, based on modified Stokesian dynamics, is presented. Its applicability extends over a wide range of particulate systems, but is in this work utilised for simulating pigment particle motion in coating colours. The particle suspension is represented by spherical rigid bodies of a given size distribution and suspended in a liquid medium. Numerical simulations performed using this technique enable the study of microscopic mechanisms, the characterisation of particle system constitution, microstructure development in time and the prediction of macro-level properties of various particle suspensions. Modifications made to the traditional Stokesian dynamics permit the simulation of particle systems comprising thousands of particles. Improvements in computational efficiency results from the estimation of hydrodynamic particle interactions by near-field lubrication forces and a Stokes drag contribution from the bulk flow field. Whilst confining the technique to concentrated suspensions, the approximation is not a limitation for pigment coating colours due to their typically high solids concentrations. Additional algorithmic methods geared towards reducing computational time and memory consumption include the sparse matrix and neighbour list techniques. The particle dynamics model includes hydrodynamic interactions, colloidal DLVO-type forces, a repulsive steric force to account for polymers adsorbed on particle surfaces and the diffusion effects of Brownian motion. The objective has been to include as many relevant physico-chemical phenomena influencing particle interactions as possible, and as coupled to the macroscopic properties of the suspension.