Creaming and aggregation of particles in suspensions

The creaming stability of suspensions of polydispersed fatty alcohol particles (2 μ m mean diameter and 29% volume concentration) in an aqueous phase containing non-ionic emulsifiers and polysaccharides relevant to antifoaming products is experimentally investigated. The observed rate of creaming increased with time until a maximum corresponding to the growth in size of particle aggregates, and decreased subsequently as aggregation ceased. The extent of particle aggregation and separation of serum are found to be high in suspensions for which the measured electrophoretic mobility is low implying weak electrostatic repulsion between particles. Analysis and testing of data published over half a century shows the equation of Garside and Al-Dibouni [J. Garside, M.R. Al-Dibouni, Ind. Eng. Chem. Process Des. Develop. 16 (1977) 206] to predict well the measured creaming velocity over wide ranges of monodispersed particle sizes, concentrations and physical properties. Based on this, a model is presented, which allows for the time dependent initial growth of aggregates due to collisions between particles, and subsequent decrease in size as large particles cream out of the suspension. The model describes well the experimentally measured kinetics of serum separation and enables characterization of the creaming stability of suspensions of polydispersed particles.