SCALING ANALYSIS OF SEDIMENT EQUILIBRIUM IN AGGREGATED COLLOIDAL SUSPENSIONS

The equilibrium of aggregated colloidal suspensions under gravity is s tudied both theoretically and experimentally. Using a simplified model to describe the compaction of the gelled suspension, we show that the volume fraction of the particles needed to form a stable gel is not i ntrinsic to the physicochemical system but depends on the height of th e sample, its aspect ratio, and the friction between the suspension an d the cell wall. A scaling analysis is developed to predict the variou s regimes encountered and to calculate the variations of the equilibri um sediment height as a function of the volume fraction of the particl es and the height, and width of the sample. Good agreement is found wi th systematic measurements performed on aqueous colloidal calcium carb onate suspensions.