Rheological Properties of Flocculated Colloidal Suspension

Abstract

The viscosity and yield stress of flocculated suspensions were reviewed in terms of fractal structure and strength of flocs. The fractal structure is formed by the sequential collision process of clusters. However, the cluster rearrangement process is important with the number of contacts between clusters. Floc strength is determined by the product of cohesive force per contact and the number of contacts between clusters. This simple expression will determine the size of flocs at given shear rate, thus determining effective volume of flocs. Shear thinning behavior is expressed by putting this value into Mori-Ototake viscosity equation. The asymptotic behavior of shear stress at zero shear limit is interpreted as yield stress. The obtained yield stress is expressed as a function of volume fraction of colloid. The functional form is different from that obtained for the flocculated sediment with vane in rather concentrated region. Importance for further analyses on the loose, soft and unstable sediment with large deformable flocs is implied.