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Universal diagram for the kinetics of particle deposition in microchannels
Why do particles, suspended in a fluid and travelling in a channel, deposit onto walls ? The question has far-reaching implications in different domains (filtering, syringeability, fouling…). Close to a channel wall, particles are subjected to a variety of effects, which control their trajectories : hydrodynamic forces, diffusion, Van der Waals attraction, and electrostatic forces. The existing theories and phenomenologies, due to their inherent limitations, and the numerical and experimental studies, due to their scarcity, did not allow thus far to establish a general description of the deposition process. By coupling microfluidic experiments, theory and numerics, we succeed to establish a general description of the phenomenon. We show the existence of three main regimes : van der Waals, Debye and Diffusive, each including various sub-regimes. Within each main regime, particle deposition is dominated either by (attractive) van der Waals forces, (repulsive) electrostatic forces, or diffusion. The ensemble of the regimes and their transitions can be displayed in diagrams. We focus on the case A/kT 1 (case of most practical interest), for which the diagram, which shapes like a Cantilever beam, involves two dimensionless numbers, P (incorporating the Debye layer characteristics) and B (function of the flow speed, diffusion constant and the geometry). The present work allows to understand empirical observations thus far left unexplained and provides a new paradigm enabling to engineer devices in a way that reduce or enhance particle deposition.