Transport of dilute suspensions in porous media with heterogeneous particle-media attractions

Porous media that find widespread use in practical applications naturally exhibit variations in their composition and surface charge. These variations create diverse physicochemical interactions between the material and particles moving through it. Nonetheless, there remains limited understanding of how these interactions influence particle transport. We employed Stokesian dynamics simulations to investigate the impact of these heterogeneous interactions on the diffusion and dispersion of particles in ordered arrays of nanoposts. Our findings reveal that, under quiescent conditions, particle transport involves two mechanisms: diffusion through open spaces and intermittent hopping between attractive sites on different nanoposts. As the degree of heterogeneity of attractions increases, the latter mechanism becomes more dominant. This leads to greater complexity in particle trajectories, deviations from the typical Gaussian behavior in particle displacement patterns, and a reduction in long-time particle diffusion. Similarly, under flow conditions characterized by low Péclet numbers (Pe), larger attraction heterogeneity causes particles to become temporarily trapped near the nanoposts, resulting in a wider particle distribution and enhanced dispersion in the direction of flow. However, at high Pe values where advection dominates, the longitudinal dispersion coefficient remains unaffected by attraction heterogeneity and follows Taylor-Aris behavior. Our study sheds light on the ways in which heterogeneous physicochemical interactions can impact the transport of particles in complex three-dimensional porous material.