Title: Geometrically Cohesive Granular Materials: Structure, Permeability and Porosity

Abstract:

Geometrically cohesive granular materials (GCGMs) are granular materials whose shape allows for particle entanglement that can result in extreme rigidity (c.f. bird nests, beaver dams and entangled clothes hangers). In this talk I’ll first review some surprising rheological features of GCGMs that arise from the collective particle interactions and introduce Super-ellipse Sector Particles, a construct that can parameterize a wide variety of particle shapes, including (pictured below) round and sickle-shaped blood cells, U-shaped staples, colloidal nanopods, long, thin rods and bent-core liquid crystals.

I’ll then describe new experiments on fluid flow through packings of large aspect-ratio granular rods which have significantly higher porosity, permeability and stability than those of ordinary, round granular materials. Practically, this allows rods used as proppant in hydraulic fracture to increase natural gas recovery rates by 10-13% and virtually eliminate the need for post-recovery processing to filter out unwanted sediment. We measure the permeability and porosity of rod packings for a variety of particle aspect ratios and container sizes and, separately, use refractive index matched (RIM) tomography to image the full 3d packing. This allows us to calculate not only bulk porosity but the size distribution for both voids and throats, where sediment clogging is most likely. We calculate the shortest connected paths across the pile as a function of intruder size and use this to predict packing filtration properties.