The dynamics of colloids in a narrow channel driven by a non-uniform force

TL;DR

This study uses simulations to explore how non-uniform forces affect colloid dynamics in narrow channels, revealing shear-induced melting, elastic-plastic transitions, and boundary effects influenced by force gradients and colloid density.

Contribution

It introduces a detailed analysis of colloid behavior under non-uniform driving forces, highlighting the transition from elastic to plastic regimes and boundary effects, which were not previously characterized.

Findings

Shear-induced melting occurs under non-uniform driving forces.

Plasticity initiates near boundaries due to density and force gradients.

System response varies with force magnitude, channel width, and colloid density.

Abstract

Using Brownian dynamics simulations, we investigate the dynamics of colloids confined in two-dimensional narrow channels driven by a non-uniform force F(y). We considered linear-gradient, parabolic and delta-like driving-force profiles. This driving force induces melting of the colloidal solid (i.e., shear-induced melting), and the colloidal motion experiences a transition from elastic to plastic regime with increasing F. For intermediate F (i.e., in the transition region) the response of the system, i.e., the distribution of the velocities of the colloidal chains, in general does not coincide with the profile of the driving force F(y), and depends on the magnitude of F, the width of the channel and the density of colloids. For example, we show that the onset of plasticity is first observed near the boundaries while the motion in the central region is elastic. This is explained by: (i) (in)commensurability between the chains due to the larger density of colloids near the boundaries, and (ii) the gradient in F. Our study provides a deeper understanding of the dynamics of colloids in channels and could be accessed in experiments on colloids (or in dusty plasma) with, e.g., asymmetric channels or in the presence of a gradient potential field.