Structure induced laminar vortices control anomalous dispersion in porous media

Abstract

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.

Spatial structure, chemotaxis and quorum sensing shape biomass accumulation in complex systems

“…Each experiment is accompanied by an independent experiment wherein the WT strain is replaced by a mutant ( E. coli Δ luxS) lacking the AI-2 synthase LuxS . First, we saturate the device with a motility buffer (10 mM potassium phosphate, 0.1 mM EDTA, 10 mM lactate, 1 mM methionine, pH 7.0), followed by a sharp injection (see [23]) of bacterial suspension. At this stage, the bacteria are suspended only within the motility buffer, which allows the injected bacteria to swim (propelled by their flagella), but not to divide and grow.…”

“…In a spatially complex micro-environment, the local availability of dissolved AI-2 is controlled by the coupling of fluid flow in advection dominated zones connecting areas of fluid stagnation [41,49]. In this work, we use microfluidic experiments and automated time-lapse video-microscopy to explore the role of different structures, Transmitting and Dead-End pores, and the consequent flow heterogeneity on bacterial colonization of a system that mimics the spatial complexities in the gut [23]. We show that flow heterogeneity translates into persistent gradients of signaling molecules and carbon resources (here, glucose) with consequences on the colonization and spatial organization of E. coli.…”

“…Microfluidic devices. We designed the porous micromodel exploiting the method of solid-state dewetting, which results in a surface morphology exhibiting spinodal-like structure and a disordered hyperuniform character described in [23]. We printed the micromodel geometry into a silicon wafer via soft lithography, depositing a layer of SU-8 2150 (MicroChem Corp., Newton, MA) with controlled thickness (0.05 mm) via spin-coating.…”

“…Numerical simulation of flow velocity. We performed a stationary creeping flow simulation using COMSOL Multiphysics over a smaller microfluidic domain of 9.6 mm × 3.6 mm with the same structure, as in [23]. The computational resolution is high enough to ensure a divergence free velocity field.…”

“…Structural properties of heterogenous environments control the flow of fluids (i.e. advection) [22,23] , transport of suspensions (e.g. bacteria) [7], solutes (e.g.…”