Structure induced laminar vortices control anomalous dispersion in porous media

Natural porous systems, such as soil, membranes, and biological tissues comprise disordered structures characterized by dead-end pores connected to a network of percolating channels. The release and dispersion of particles, solutes, and microorganisms from such features is key for a broad range of environmental and medical applications including soil remediation, filtration and drug delivery. Yet, owing to the stagnant and opaque nature of these disordered systems, the role of microscopic structure and flow on the dispersion of particles and solutes remains poorly understood. Here, we use a microfluidic model system that features a pore structure characterized by distributed dead-ends to determine how particles are transported, retained and dispersed. We observe strong tailing of arrival time distributions at the outlet of the medium characterized by power-law decay with an exponent of 2/3. Using numerical simulations and an analytical model, we link this behavior to particles initially located within dead-end pores, and explain the tailing exponent with a hopping across and rolling along the streamlines of vortices within dead-end pores. We quantify such anomalous dispersal by a stochastic model that predicts the full evolution of arrival times. Our results demonstrate how microscopic flow structures can impact macroscopic particle transport. Most porous systems comprise structures characterized by dead-end and transmitting pores. Here, authors show that macroscopic transport through such porous medium is controlled by structure-induced laminar vortices inside each dead-end pore, and such cannot be explained by diffusion alone.

Automated summary

This study investigates the influence of dead-end pore structure on particle transport and dispersion using a microfluidic model system. The authors observe a tailing phenomenon in the arrival time distribution and explain it as a result of hopping and rolling of particles within dead-end pores. The results demonstrate the impact of microscopic flow structures on macroscopic particle transport.