Shear thinning and shear thickening in colloidal suspensions

shear thinning and shear thickening are two phenoma commonly observed when colloidal suspensions flow. Shear thinning corresponds to a decrease of the viscosity as the shear rate increases while shear thickening corresponds to an increase of the viscosity as the shear rate increases. Here, we will use a dispersion of carbon black particles (fractal colloidal particles of diameter 70nm) in oil to study the shear thinning effect and a dispersion of fumed silica particles (fractal colloidal particles of diameter 300nm) dispersed in Polypropylene glycol. Time Resolved Ultra Small Angle X-ray Scattering coupled to rheology will be used to monitor the structure of the dispersion along its flow curve. Decreasing the shear rate in shear thinning carbon black dispersions should lead to larger and larger clusters while we believe that it is the contrary in shear thickening fumed silica dispersions.