# Shear-induced laning transition in a confined colloidal film

## TL;DR

This study uses Brownian dynamics simulations to reveal how shear flow induces lane formation and structural transitions in confined colloidal films, significantly affecting their rheological properties.

## Contribution

It uncovers the shear-induced laning transition in a three-layer colloidal film, a phenomenon not previously characterized in such confined systems.

## Key findings

- Shear flow causes the middle layer to split into two lanes with opposite velocities.
- Laning disrupts the shear profile and alters the system's rheology.
- At high shear, the system becomes disordered and then recrystallizes, similar to bilayer behavior.

## Abstract

Using Brownian dynamics (BD) simulations we investigate a dense system of charged colloids exposed to shear flow in a confined (slit-pore) geometry. The equilibrium system at zero flow consists of three, well-pronounced layers with square-like crystalline in-plane structure. We demonstrate that, for sufficiently large shear rates, the middle layer separates into two sublayers where the particles organize into moving lanes with opposite velocities. The formation of this micro-laned state results in a destruction of the applied shear profile. It has a strong impact not only on the structure of the system, but also on its rheology as measured by the stress tensor. At higher shear rates we observe a disordered state and finally a recrystallization reminiscent of the behavior of bilayer films. We expect the shear-induced laning to be a generic feature of thin films with three or more layers.