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 ${\phi }_m=0.60\mathrm{}$ indicate that the particles can be modeled as Brownian hard spheres. Above this ${\phi }_m$ the flow 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.