BROWNIAN-DYNAMICS SIMULATIONS OF MODEL STABILIZED COLLOIDAL DISPERSIONS UNDER SHEAR

We have continued our investigation of the effect of shear flow on the microstructure of model near-hard-sphere dispersions by using the com puter simulation technique of Brownian dynamics (BD) in the approximat ion ignoring many-body hydrodynamics. We have determined a non-equilib rium phase diagram that gives the shear rate at which there is a trans ition 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 scatte ring intensities) from the model system under shear, subject to slidin g periodic boundary conditions. The relationship between the real spac e 'snap-shot' configurations and these structure factors is thereby el ucidated. We also make a quantitative comparison between the scatterin g intensities obtained by recent light-scattering experiments and thos e 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 fra ctions and infinite shear rates, which the experiments do not confirm.