# Unjamming of particle–laden interfaces: effects of geometry and history

## TL;DR

This paper studies how compressed particle layers unjam when a hole is opened, revealing different unjamming behaviors influenced by geometry and preparation history.

## Contribution

The study identifies three distinct unjamming behaviors and shows how geometry and preparation history affect stress relaxation in particle rafts.

## Key findings

- Minimal unjamming does not allow significant relaxation in particle rafts.
- Axial unjamming creates a channel that may extend through the raft and lead to partial stress relaxation.
- Lateral unjamming via erosion causes significant stress relaxation after axial unjamming.

## Abstract

The unjamming of uniaxially compressed particle rafts triggered by the opening of a finite orifice on the opposite side is experimentally studied. Using glass beads of about 100 μm, three main behaviors are identified. Minimal unjamming does not allow significant relaxation. Axial unjamming corresponds to the growth of the unjammed domain along the compression direction with an almost constant width. The resulting channel, possibly extends through the entire raft length and may lead to partial stress relaxation. Finally, after the completion of axial unjamming, lateral unjamming may occur according to an erosion process during which jammed blocks detach from the channel edges. This is associated with important stress relaxation. By using different raft geometries, i.e. various raft lengths, compression levels, and opening widths, we rationalize the occurrence of these behaviors, attributing them to the rupture of the force chain network against shear and elongation, respectively. Comparing results from equally densely packed rafts prepared with three different protocols demonstrates that these two thresholds are strongly affected by the raft's history.

Compressed particle rafts are left to flow through a finite orifice placed opposite to the compressive barrier. Top view pictures evidence the influence of the opening width and raft history on raft unjamming (red) and particle release (blue).