(584e) Leveraging Viscoelastic Flow Instabilities for Remediation of Soiled Porous Media

The pollution of groundwater aquifers by microplastics, biofilms, and other chemical contaminants presents an urgent need for safe and efficient remediation strategies. One proposed remediation method involves the injection of viscoelastic fluids into the subsurface environment: a process actively employed in enhanced oil recovery. However, how exactly viscoelasticity of the displacing fluid may influence particle mobilization from surfaces in a 3D, spatially complex environment remains largely unexplored. Here, we investigate the flow-induced removal of deposited microplastics from a model porous medium using injection of a viscoelastic dilute polymer solution. We use fluid refractive index-matching and confocal microscopy to directly visualize the pore-scale dynamics of particle removal under imposed fluid flow, and further quantify the 3D morphology of deposits and overall particle deposition profile across the medium. Under matched flow rate conditions, we find that polymer solution injection—above a threshold flow rate—achieves greater removal efficacy compared to an equivalent flow of a viscous Newtonian solvent. We hypothesize that the improved cleaning performance of the polymer solution results from two mechanisms: (1) increased extensional stresses along and away from surfaces arising from elongation of polymer chains as they traverse the tortuous pore space, and (2) the onset of an elastic flow instability that produces chaotic spatiotemporal flow fluctuations—even at low Reynolds number. These mechanisms in turn modulate both the local drag and lift forces acting on deposits, which collectively enhance removal of the particles compared to the largely viscous drag-dominated mode of removal for Newtonian fluids. Our work thus provides important insight into the in situ removal dynamics of microplastics in geometrically-complex environments and highlights the exciting potential of viscoelastic fluid flows towards the remediation of contaminated porous media.