Brownian-dynamics simulations of model stabilised colloidal dispersions under shear

Abstract

We have continued our investigation of the effect of shear flow on the microstructure of model near-hard-sphere dispersions by using the computer simulation technique of Brownian dynamics (BD) in the approximation ignoring many-body hydrodynamics. We have determined a non-equilibrium phase diagram that gives the shear rate at which there is a transition between an amorphous liquid-like structure at low shear rate to an ordered phase at high shear rates, as a function of the fraction of solids. We have derived the mathematical Fourier-transform procedure needed to compute the structure factor (and therefore predicted scattering intensities) from the model system under shear, subject to sliding periodic boundary conditions. The relationship between the real space ‘snap-shot’ configurations and these structure factors is thereby elucidated. We also make a quantitative comparison between the scattering intensities obtained by recent light-scattering experiments and those predicted by our model. There is some qualitative agreement between the experimental and simulation intensites for moderate shear thinning; however, the model forms an ordered ‘string’ phase at low volume fractions and infinite shear rates, which the experiments do not confirm.