The structure of pores both grant a granular pack it's structural stability, as well as granting fluid a path to flow through this granular pack. The details of these pores can therefore determine the depth of water penetration, the ability of the medium to sustain a compressive load, or the liquification of the pack under extreme fluid pressure. Therefore, understanding how the microstructures of granular packs contribute to stability, flows, and dynamics of the bulk medium is a crucial question for anyone making use of these soils and other granular packs.

Droplet Dynamics in Microfluidic Porous Media

Droplets moving through porous media are a relevant question to those working on the cleanup of PFAS, a polluting surfactant that travels through groundwater. We study these systems in a microfluidic flow cell, with a Poisson disk pattern providing the obstacles of a high-porosity medium. We notice droplets in this system quickly change size via coalescence and breakup. Regardless of what size or polydispersity you inject the droplets, they arrive at a certain size distribution after a long time or distance down the chamber, set my the flow and channel geometries. This behavior is predictable from the microscopic breakup and coalescence dynamics. We are also able to characterize the flow of soft droplets perpendicular to the flow velocity, cast as an effective diffusion constant as a function of droplet softness.

Random Close Packing of Polydisperse Grains

A classic question is to try to guess the number of marbles in a jar, or the "packing fraction". This concept has been highly studied in monodisperse circle systems, but changing the size variety of the circles complicates the packing significantly. One significant change is the increased variety of circle packs; a single polydispersity (based on circle radii) could be generated by many different probability distribution functions (PDFs), that could all pack differently. We find that the individual PDF does not affect the packing besides the polydispersity and skewness of that PDF, and by just knowing the PDF, we can predict the circle packing fraction.