Granular dynamics simulations of colloidal suspensions: Scaling effects of stabilisation forces

Abstract

Steady-state shear flow granular dynamics simulations have been used to study the effects of interparticle repulsions in colloidal suspensions using a soft-sphere model effective-pair potential defined by φ(rij) = ε(rij/σ - 1)-n where σ is a hard-core collision diameter and ε is a repulsive pair energy. When the thermal energy is 10mε the equilibrium osmotic pressures of the model suspensions are found to scale with an effective hard-core diameter given by σeff = σ(1 + 10-m/n)) predicting osmotic pressures in accord with available experimental data for electrostatically stabilised monodisperse latex suspensions. The stress vs. shear rate flow curves are obtained initially in the isokinetic model by velocity scaling for three dense fluid states over a range of shear rates. A correspondence between the isokinetic flow curves (constant 'granular temperature') and mean-field Stokesian flow curves (constant friction coefficient) over the whole range of shear rate is shown numerically. The predicted laboratory flow curves for the tensors of pressure, energy and diffusivity are compared with previous hard-sphere model results and with a general body of experimental data from rheometry of monodisperse latices.