(255f) Hydrodynamic Interactions Effect on the Aggregation of Colloidal Dispersions in the Presence of Sedimentation

Aggregation of colloidal particles plays a crucial role in many processes of both fundamental and practical importance. For environmental applications, such as in waste-water treatment, sedimentation is one of most important driving forces for cluster formation. While many investigations have been carried out aiming at understanding the role of sedimentation in combination with diffusion and interparticle interactions in determining structure and aggregation rate of particles, one effect has almost always been neglected: the role played by hydrodynamic interactions. In this work, we have investigated the role played by hydrodynamics using Fast Lubrication Dynamics. In our simulations, we used a strategy already proposed a couple of decades ago in the investigation of sedimentation by means of Monte-Carlo simulations. Particles have been randomly positioned in a virtual box, and moved according to Langevin equation, including long- and short-range hydrodynamic interactions, Van der Waals forces, diffusion and sedimentation. The second major novelty of our work, in addition to hydrodynamics, is the presence of contact forces, which have also been included in the simulations to realistically account for the deformation of clusters subject to sedimentation. Particles are subject to periodic boundary conditions in all spatial directions, which are suitable to simulate what happens in the middle of a real suspension subject to sedimentation, i.e., far from the upper and lower boundaries of the system. The results of the simulation are compared to the case where hydrodynamic interactions are neglected. The results show the strong role played by such interactions, and the interplay of hydrodynamics and contact forces in the evolution of the structure of the aggregated formed under these conditions.