Compression and fracture of ordered and disordered droplet rafts

TL;DR

This study uses simulations to investigate how ordered and disordered droplet arrays fracture under compression, revealing the influence of array structure and size on fracture behavior and force response.

Contribution

It provides new insights into the fracture mechanisms of droplet rafts, especially how order, size, and polydispersity affect rupture dynamics under compression.

Findings

Ordered arrays show a force peak before fracture.

Larger arrays exhibit multiple, competing fractures.

Polydispersity disrupts fracture patterns and force responses.

Abstract

We simulate a two-dimensional array of droplets being compressed between two walls. The droplets are adhesive due to an attractive depletion force. As one wall moves toward the other, the droplet array is compressed and eventually induced to rearrange. The rearrangement occurs via a fracture, where depletion bonds are quickly broken between a subset of droplets. For monodisperse, hexagonally ordered droplet arrays, this fracture is preceded by a maximum force exerted on the walls, which drops rapidly after the fracture occurs. In small droplet arrays a fracture is a single well-defined event, but for larger droplet arrays, competing fractures can be observed. These are fractures nucleated nearly simultaneously in different locations. Finally, we also study the compression of bidisperse droplet arrays. The addition of a second droplet size further disrupts fracture events, showing differences between ideal crystalline arrays, crystalline arrays with a small number of defects, and fully amorphous arrays. These results are in good agreement with previously published experiments.