Steady shear behavior of polymerically stabilized suspensions: Experimentsand lubrication based modeling

Flow curve measurements are presented of a suspension of polymerically stab ilized monodisperse spheres, with a polymer layer thickness of 0.7 times th e 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 plateau s 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 b ehavior, due to the direct contact between polymer layers of different sphe res. At high shear rates the onset of Newtonian plateaus is observed with a gradual concentration dependence. The experimental high shear data are com pared with model calculations, based on the dissipation due to lubrication forces treating the polymer layer as a Brinkman medium. The model we used w as adapted to give a better description of the polymer layer. Fitting the e xperiments to obtain the permeability of the polymer layer, we found a valu e in the range of values expected from polymer theory. Our adapted lubricat ion model was also used to reanalyze experimental data for other polymerica lly stabilized suspensions. [S1063-651X(99)02703-8].