Particle Deposition Kinetics of Colloidal Suspensions in Microchannels at High Ionic Strength.

ABSTRACT

Despite its considerable practical importance, the deposition of real Brownian particles transported in a channel by a liquid, at small Reynolds numbers, has never been described at a comprehensive level. Here, by coupling microfluidic experiments, theory, and numerics, we succeed in unravelling the problem for the case of straight channels at high salinity. We discover a broad regime of deposition (the van der Waals regime) in which particle-wall van der Waals interactions govern the deposition mechanism. We determine the range of existence of the regime, for which we calculate the concentration profiles, retention profiles, and deposition kinetics analytically. The retention profiles decay as the inverse of the square root of the distance from the entry, and the deposition kinetics are given by the expression [Formula see text], where S is a dimensionless deposition function, A is the Hamaker constant, and ξL is a dimensionless parameter characterizing fluid flow properties. These findings are well supported by numerics. Experimentally, we find that the retention profiles behave as x-0.5±0.1 (where x is the distance from the channel entry) over three decades in scale, as predicted theoretically. By varying the flow conditions (speed, geometry, surface properties, and concentration) so as to cover four decades in ξL and taking the Hamaker constant as a free parameter, we accurately confirm the theoretical expression for the deposition kinetics. Operating in the van der Waals regime enables control of the deposition rates via surface chemistry. From a surface science perspective, working in the van der Waals regime enables us to measure the Hamaker constants of thousands of particles in a few minutes, a task that would take a much longer time to perform with standard AFM.