Nanoparticle dispersion in porous media: Effects of array geometry and flow orientation

Particle dispersion through porous media with heterogeneous attractions

“…Imposed suspension velocities V N = 0-1000 resulted in Pe = 0-10 3 , covering the range accessible in experiment and relevant to probing regimes dominated by different transport mechanisms. 71,78,80,86 In the absence of attractions (u 0 = 0), D L /D 0 increases gradually with Pe for 10 0 r Pe r 10 1 (Fig. 6).…”

“…Here, d p is the particle diameter, k B is the Boltzmann constant, T is temperature, t d is the diffusive time scale, and Z is the dynamic fluid viscosity. Following our previous studies, 35,42,78 each nanopost was modeled as an immobile chain of 20 spherical beads of diameter d np = d p . The arrays consisted of 100 Â 100 nanoposts placed on a regular square lattice in the x-y plane of the simulation cell with their major axes aligned along the z direction (Fig.…”

“…Other details of SD simulations are identical to those in our previous studies. 35,42,78 Transport properties were determined by averaging over approximately 100 independent particle trajectories. Under quiescent conditions (i.e., V N = 0), the particle diffusivity was extracted from the long-time limit of the ensemble-averaged, three-dimensional mean-squared displacement (MSD), D q ¼ lim t!1…”

“…At large Pe (Pe Z 10 1 ), where advective transport is dominant, D L /D 0 increases rapidly and eventually crosses over to Pe n scaling with n E 2, as predicted for Taylor-Aris dispersion. 12,78,87 Longitudinal dispersion is increasingly enhanced for Pe Z 10 1 as the attraction strength u 0 is increased. For systems with low heterogeneity (b r 2), the increase in D L /D 0 is relatively uniform for Pe Z 10 1 .…”

“…In our previous study of particle transport in square and hexagonal arrays with repulsive, non-hydrodynamic particle-nanopost interactions (i.e., u 0 = 0), we observed a pronounced reduction in mean particle velocity and longitudinal dispersion for flow orientations slightly offset from the primitive lattice vectors. 78 This reduction was caused by directional locking, where steric interactions with the nanoposts lead to particle dynamics dominated by advection along a specific vector across a range of y. 23 In the context of practical applications, this phenomenon can be exploited in deterministic lateral displacement devices to sort particles by size.…”