The Observation of Formation and Annihilation of Solitons and Standing Strain Wave Superstructures in a Two-Dimensional Colloidal Crystal

TL;DR

This study investigates the formation, stability, and annihilation of solitons and strain wave superstructures in a confined two-dimensional colloidal crystal, revealing how boundary conditions influence defect patterns and strain distribution.

Contribution

It introduces a coarse-grained dynamic model to analyze soliton behavior and strain patterns in colloidal crystals under confinement, highlighting the role of structured walls.

Findings

Solitons form along boundaries with structured walls under compression.

Defect structures resemble soliton staircases affecting strain distribution.

Dynamics of soliton formation and annihilation are characterized and visualized.

Abstract

Confining a colloidal crystal within a long narrow channel produced by two parallel walls can be used to impose a meso-scale superstructure of a predominantly mechanical elastic character [Chui et al., EPL 2008, 83, 58004]. When the crystal is compressed in the direction perpendicular to the walls, we obtain a structural transition when the number of rows of particles parallel to the walls decreases by one. All the particles of this vanishing row are distributed throughout the crystal. If the confining walls are structured (say with a corrugation along the length of the walls), then these extra particles are distributed neither uniformly nor randomly; rather, defect structures are created along the boundaries resembling "soliton staircases", inducing a non-uniform strain pattern within the crystal. Here we study the conditions of stability, formation and annihilation of these solitons using a coarse grained description of the dynamics. The processes are shown by comparing superimposed configurations as well as molecular animations obtained from our simulations. Also the corresponding normal and shear stresses during the transformation are calculated. A study of these dynamical processes should be useful for controlling strain wave superstructures in the self-assembly of various nano- and meso scaled particles.