MULTILAYER DEPOSITION OF STABLE COLLOIDAL PARTICLES DURING FLOW WITHIN CYLINDRICAL PORES

Multilayer deposition of stable colloidal particles during the low Rey nolds number flow of aqueous suspensions of latex particles through cy lindrical pores in track-etched membranes has been experimentally stud ied. Though multilayer deposition or the role of deposited particles a s additional collectors has been recognized before this work, the reas on multilayer deposition of particles occurs in the presence of strong interparticle repulsion and the interactions governing the transition from single layer to multilayer deposition have not been elucidated. Because sufficient repulsion exists between particles in a stable susp ension to prevent their aggregation by Brownian flocculation, the depo sition of particles on top of previously deposited particles to form m ultilayers is flow-induced. In this paper, we first show that only a s ingle layer of particles will be deposited on the pore surface if stro ng repulsion exists between particles. We then demonstrate the transit ion from single layer to multilayer deposition at a sufficiently high flow rate when the interparticle repulsion is reduced by adding an ele ctrolyte (but not exceeding the critical flocculation concentration). Under these conditions, the hydrodynamic force acting on a flowing par ticle in the vicinity of a deposited particle can overcome the net int erparticle repulsion and multilayers of particles can accumulate withi n the pores. Approximate calculations of the trajectory of a flowing p article in the vicinity of a stationary particle that qualitatively de monstrate the flow-induced nature of the phenomenon are also presented .