THE TRANSIENT SETTLING OF STABLE AND FLOCCULATED DISPERSIONS

An experimental investigation of the sedimentation of monodisperse colloidal silica spheres with grafted octadecyl chains with three different interaction potentials is presented. Small particles (0.27-mu-m) behaved as hard spheres in cyclohexane, but larger ones (0.60 and 0.94-mu-m) are weakly flocculated by van der Waals attractions. The smallest particles (0.08-mu-m) in hexadecane are strongly flocculated by attractions between the octadecyl layers. A medical computer tomography (CT) scanner provided an accurate and absolute density measurement without disrupting the process. For the hard spheres and the weakly flocculated systems, the kinetics of sedimentation for the dispersed phase could readily be predicted utilizing the flux curve. For flocculated networks, we found a power-law relationship between compressive yield stresses and solids fractions comparable with other experimental systems.