Steady shear behavior of polymerically stabilized suspensions: Experiments and lubrication based modeling

Flow curve measurements are presented of a suspension of polymerically stabilized monodisperse spheres, with a polymer layer thickness of 0.7 times the core radius. At low shear rates a drastic change in behavior occurs at a critical (effective) volume fraction phi(m). Below phi(m) the curves show a low shear Newtonian plateau. The concentration dependence of these plateaus together with phi(m) = 0.60 indicate that the particles can be modeled as Brownian hard spheres. Above this phi(m) the how curves indicate plastic behavior, due to the direct contact between polymer layers of different spheres. At high shear rates the onset of Newtonian plateaus is observed with a gradual concentration dependence. The experimental high shear data are compared with model calculations, based on the dissipation due to lubrication forces treating the polymer layer as a Brinkman medium. The model we used was adapted to give a better description of the polymer layer. Fitting the experiments to obtain the permeability of the polymer layer, we found a value in the range of values expected from polymer theory. Our adapted lubrication model was also used to reanalyze experimental data for other polymerically stabilized suspensions. [S1063-651X(99)02703-8].