Rheology of Colloidal Particles in a Confined Channel under Shear Flow by Brownian Dynamic Simulations

A colloidal system of strongly charged particles, confined between two charged walls, is studied under static conditions and in the presence of shear flows. Brownian Dynamics simulations (BD) are used to determine the concentration profiles for several separations of charged walls. Results show good agreement with those obtained under static conditions using the Hypernetted Chain Approximation (HNC) and Monte Carlo simulations. Results obtained with BD and HNC for neutral walls show more similarities than those between BD and Monte Carlo simulations depending on the initial state of the colloidal particles. The presence of a shear flow field perturbs the equilibrium concentration profiles and the distribution function in the flow direction, generating a structureless system, as confirmed by the absence of peaks in the radial distribution function. The mobility of the particles in the transversal direction decreases rapidly and becomes practically frozen. The flow exhibits a non-Newtonian behavior with shear-thinning viscosity. Due to the interparticle interactions and particle-wall interactions, the viscosity is lower as the wall separation decreases, giving rise to an apparent slip in the colloidal suspension. The slip velocity for repulsive walls is higher than that obtained with neutral walls and increases with the shear stress according to a power law, as observed in polymer solutions. The shear viscosity and the normal stress differences depend strongly on the combined effect of confinement, concentration of particles, magnitudes of inter-particle interactions and wall-particle repulsion.