Brownian Dynamics simulation of hard-sphere colloidal dispersions

The rheology of hard-sphere suspensions in the absence of hydrodynamic inte ractions is examined by Brownian Dynamics. Simulations are performed over a wide range of volume fraction phi and Peclet number Pe = (gamma) over dota (2)/D, where (gamma) over dot is the shear rate and D = kT/6 pi eta a is th e Stokes-Einstein diffusivity of an isolated spherical particle of radius a and thermal energy kT in a fluid of viscosity eta. At low Pe, the viscosit y decreases as Pe increases-the suspension shear thins. The first normal st ress difference is positive, while the second normal stress difference is n egative. Each normal stress difference vanishes at very low Pe and increase s in magnitude to an extremum at Pe approximate to 3. The suspension pressu re is proportional to kT and is found to grow as Pe(2) from its equilibrium value. Long-time self-diffusivities scale as D and grow as Pe is increased in this regime. At Pe approximate to 100, the suspension undergoes a disor der-order transition to a microstructure of hexagonally packed strings alig ned in the flow direction, which is accompanied by precipitous drops in the viscosity, pressure and long-time self diffusivities. At high Pe, all comp onents of the stress tensor scale as eta(gamma) over dot and the diffusivit ies scale as (gamma) over dota(2). Viscosity data for a wide range of phi a nd Pe are collapsed using scaling theories. (C) 2000 The Society of Rheolog y. [S0148-6055(00)00403-X].