Particle sedimentation: effect of polymer concentration on particle–particle interaction

Sedimentation not only controls some important industrial processes but also is a readily available tool for particle separation, determination of particle size and particle size distribution. Velocity of sedimentation is a controlling parameter in this process. The hydrodynamic forces of the system, interactions of particles with matrix and with each other control this parameter. In highly filled suspensions, particle–particle interactions affect sedimentation more than the hydrodynamic and particle–matrix interaction. Existence of polymer in the matrix would change matrix viscosity, affecting hydrodynamic motion of particles; and adsorption of polymer on the surface of particles would change surface properties, causing alteration in particle–matrix and particle–particle interactions. This work is a study of effect of polymer concentration on particle–particle interactions. The results show that at low particle concentrations, addition of a small amount of polymer in the solution would decrease particle–particle interactions. However, in a highly filled suspension, polymer does not affect particle–particle interactions. Toluene was used as the solvent, nano-silica as the particle and polystyrene as the polymer. A high shear mixer was used to reduce the agglomeration of nano-silica particles, especially for highly filled suspensions. Sedimentation tests were performed in columns with a length of 50 cm and 26 mm in diameter.