Avalanches, Plasticity, and Ordering in Colloidal Crystals Under Compression

TL;DR

This study uses simulations to explore how colloidal crystals respond to compression, revealing elastic distortions, avalanches of plastic rearrangements, and ordering changes, with implications for understanding dislocation dynamics and hysteresis.

Contribution

It demonstrates the occurrence of shear banding and avalanche dynamics in colloidal crystals under compression, highlighting the role of plastic events and ordering transitions in two-dimensional systems.

Findings

Avalanches involve shear banding and lattice rearrangements.

Velocity distributions during avalanches have power law tails.

Hysteresis indicates irreversibility of plastic events.

Abstract

Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compressions, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or even smectic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.