Spontaneous Patterning of Confined Granular Rods

TL;DR

This study investigates how vertically vibrated rod-shaped granular materials confined in quasi-2D form various patterns, including a density-dependent isotropic-nematic transition and complex boundary-influenced structures, modeled with continuum elastic theory.

Contribution

It demonstrates the spontaneous patterning and phase transitions of granular rods under vibration, supported by experiments, simulations, and a continuum elastic model.

Findings

Density-dependent isotropic-nematic transition observed.

Wetting layers form along the container walls.

Complex patterns emerge at high densities due to bulk-boundary interactions.

Abstract

Vertically vibrated rod-shaped granular materials confined to quasi-2D containers self organize into distinct patterns. We find, consistent with theory and simulation, a density dependent isotropic-nematic transition. Along the walls, rods interact sterically to form a wetting layer. For high rod densities, complex patterns emerge as a result of competition between bulk and boundary alignment. A continuum elastic energy accounting for nematic distortion and local wall anchoring reproduces the structures seen experimentally.