# Random packing of rods in small containers

## TL;DR

This study investigates how rods of various aspect ratios pack randomly in small containers through experiments and simulations, revealing boundary effects and the influence of gravity on packing density.

## Contribution

It provides new insights into boundary effects and the role of gravity in the packing of rods, combining experimental and simulation approaches across different aspect ratios.

## Key findings

- Boundary effects extend about half a particle length into the interior.
- Packing density decreases with smaller container size.
- Gravity influences boundary effects differently in experiments and simulations.

## Abstract

We conduct experiments and simulations to study the disordered packing of rods in small containers. Experiments study cylindrical rods with aspect ratio ranging from 4 to 32; simulations use of spherocylinders with similar aspect ratios. In all cases, rods pack randomly in cylindrical containers whose smallest dimension is larger than the rod length. Packings in smaller containers have lower volume fractions than those in larger containers, demonstrating the influence of the boundaries. The volume fraction extrapolated to infinite container size decreases with increasing aspect ratio, in agreement with previous work. X-ray tomography experiments show that the boundary effects depend on the orientation of the boundary, indicating a strong influence of gravity, whereas the simulation finds boundary effects that are purely geometric. In all cases, the boundary influence extends approximately half a particle length into the interior of the container.