Exploiting shape to control percolation of grain boundaries in packings of ellipsoids on curved surfaces

Packings of hard objects provide insights into the properties of crystals, glasses and granular media. When the packing occurs on a curved surface, it requires defects to accommodate the curvature. For identical spheres packed on a spherical surface, the packings are largely crystalline with grain boundaries or “scars”, while for sufficiently polydisperse spheres the packings typically form an amorphous state. We recently showed that these regimes can be connected by a percolation transition on the neighbor graph, whereby the scars grow as a function of particle size anisotropy. Here we show that manipulating particle shape can cause a similar transition. Ellipsoids of varying aspect ratio are packed on a spherical surface with scars at low aspect ratio; these scars elongate and disconnect the crystalline regions with increasing aspect ratio. The cluster growth and scaling are shown to agree with percolation theory. The influence on the cluster growth of interactions between the particle shape and the surface on which they are packed will also be presented, as well as prospects for the exploitation of other particle shapes, such as chiral particles, to control the transition.