Dynamic capillary assembly of colloids at interfaces with 10,000g accelerations

TL;DR

This study investigates the behavior of colloidal monolayers at interfaces under extreme, high-rate deformation driven by ultrasound, revealing inertial effects and transient network formation at accelerations near 10,000g.

Contribution

It demonstrates the first observation of inertial effects in colloids under extreme accelerations and visualizes microstructural evolution during high-rate deformation.

Findings

Inertial effects observed at 10,000g accelerations.

Transient string networks form during high-rate deformation.

Dynamic capillarity and hydrodynamics drive microstructure evolution.

Abstract

Extreme deformation of soft matter is central to our understanding of the effects of shock, fracture, and phase change in a variety of systems. Yet, despite, the increasing interest in this area, far-from-equilibrium behaviours of soft matter remain challenging to probe. Colloidal suspensions are often used to visualise emergent behaviours in soft matter, as they offer precise control of interparticle interactions, and ease of visualisation by optical microscopy. However, previous studies have been limited to deformations that are orders of magnitude too slow to be representative of extreme deformation. Here we use a two-dimensional model system, a monolayer of colloids confined at a fluid interface, to probe and visualise the evolution of the microstructure during high-rate deformation driven by ultrasound. We observe the emergence of a transient network of strings, and use discrete particle simulations to show that it is caused by a delicate interplay of dynamic capillarity and hydrodynamic interactions between particles oscillating at high-frequency. Remarkably, we find evidence of inertial effects in a colloidal system, caused by accelerations approaching 10,000g. These results also suggest that extreme deformation of soft matter offers new opportunities for pattern formation and dynamic self-assembly.