# Edges control clustering in levitated granular matter

## TL;DR

This paper demonstrates that acoustic levitation can induce highly directional forces along edges of macroscopic particles, enabling control over cluster shapes and interactions in granular matter.

## Contribution

It introduces a novel method to tune interactions between macroscopic particles using acoustic levitation, revealing edge-dependent contact forces and diverse cluster formations.

## Key findings

- Edges control contact forces in levitated granular clusters
- Edge curvature directly influences force magnitude
- Diverse cluster shapes emerge from directional interactions

## Abstract

The properties of small clusters depend dramatically on the interactions between their constituent particles. However, it remains challenging to design and tune the interactions between macroscopic particles, such as in a granular material. Here, we use acoustic levitation to trap macroscopic grains and induce forces between them. Our main results show that particles levitated in an acoustic field prefer to make contact along sharp edges. The radius of curvature of the edges directly controls the magnitude of these forces. These highly directional interactions, combined with local contact forces, give rise to a diverse array of cluster shapes. Our results open up new possibilities for the design of specific forces between macroscopic particles, directing their assembly, and actuating their motion.