Structural evolution of cuboidal granular media

Mono- and bi-disperse rectangular cuboidal granules are assembled from colloid-hydrogel suspensions via stop-flow lithography and fully submerged in hexadecane. Their packing density and structural evolution are studied as a function of agitation time using micro-computed X-ray tomography. When subjected to periodic agitation, the granule packing density increases logarithmically in time; concomitantly, the nearest-neighbor separation distance between granules decreases. Akin to spherical granular media, the distributions of Voronoi volume for these granule packings can be scaled using a shifted k-gamma probability distribution. This Boltzmann-type distribution maximizes packing entropy, indicating that the statistical mechanics approach to granular fluctuations is valid for non-spherical granular media.