Ma. Valdez et O. Manero, RHEOLOGY OF COLLOIDAL PARTICLES IN A CONFINED CHANNEL UNDER SHEAR-FLOW BY BROWNIAN DYNAMIC SIMULATIONS, Journal of colloid and interface science, 190(1), 1997, pp. 81-91
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 (ED) are used to determ
ine the concentration profiles for several separations of charged wall
s. Results show good agreement with those obtained under static condit
ions using the Hypernetted Chain Approximation (HNC) and Monte Carlo s
imulations. Results obtained with ED and HNC for neutral walls show mo
re similarities than those between ED and Monte Carlo simulations depe
nding on the initial state of the colloidal particles. The presence of
a shear flow field perturbs the equilibrium concentration profiles an
d the distribution function in the flow direction, generating a struct
ureless system, as confirmed by the absence of peaks in the radial dis
tribution function. The mobility of the particles in the transversal d
irection decreases rapidly and becomes practically frozen. The flow ex
hibits a non-Newtonian behavior with shear-thinning viscosity. Due to
the interparticle interactions and particle-wall interactions, the vis
cosity is lower as the wall separation decreases, giving rise to an ap
parent slip in the colloidal suspension. The slip velocity for repulsi
ve walls is higher than that obtained with neutral walls and increases
with the shear stress according to a power law, as observed in polyme
r solutions. The shear viscosity and the normal stress differences dep
end strongly on the combined effect of confinement, concentration of p
articles, magnitudes of inter-particle interactions and wall-particle
repulsion. (C) 1997 Academic Press.