Structural and elastic properties of a confined 2D colloidal solid: a molecular dynamics study

TL;DR

This study uses molecular dynamics simulations to explore how confinement affects the structural and elastic properties of a 2D colloidal solid, revealing boundary condition sensitivities and incommensurability effects.

Contribution

It provides new insights into the influence of confinement and boundary conditions on the structural and elastic properties of 2D colloidal crystals.

Findings

Orientational order persists near walls at high temperatures.

Incommensurability significantly alters system properties.

Elastic constants depend on density and channel width.

Abstract

We implement molecular dynamics simulations in canonical ensemble to study the effect of confinement on a $2d$ crystal of point particles interacting with an inverse power law potential proportional to $r^{-12}$ in a narrow channel. This system can describe colloidal particles at the air-water interface. It is shown that the system characteristics depend sensitively on the boundary conditions at the two {\it walls} providing the confinement. The walls exert perpendicular forces on their adjacent particles. The potential between walls and particles varies as the inverse power of ten. Structural quantities such as density profile, structure factor and orientational order parameter are computed. It is shown that orientational order persists near the walls even at temperatures where the system in the bulk is in fluid state. The dependence of elastic constants, stress tensor elements, shear and bulk modulii on density as well as the channel width is discussed. Moreover, the effect of channel incommensurability with the triangular lattice structure is discussed. It is shown that incommensurability notably affects the system properties. We compare our findings to those obtained by Monte Carlo simulations and also to the case with the periodic boundary condition along the channel width. .