Characterization of particle aggregation in a colloidal suspension of magnetite particles

We investigate relation between hydrodynamic transport properties of a colloidal suspension of magnetite particles and aggregation of the particles. The magnetite particles are of 0.3 μm in diameter and are dispersed in Newtonian ethylene glycol. The volume fraction of the particles in the suspension ranges from 0.003 to 0.04. Shear viscosity and average sedimentation velocity of the suspension are measured as a function of the particle volume fraction. To predict the aggregation of the suspended particles particle-scale analysis of sedimentation and viscosity behavior of the suspension is correlated with scaling theories for fractal aggregates. The sedimentation velocity as a function of particle concentration gives the fractal dimension of 1.91 for the magnetite aggregates in the suspension. Shear dependence of the aggregate size which is expressed by a power law is determined from intrinsic viscosity for the aggregates and yield stress of the suspension, respectively. It is found that the shear dependence from intrinsic viscosity is in good agreement with that from yield stress.