Nematic-Isotropic Interfaces Under Shear: A Molecular Dynamics Simulation

TL;DR

This study uses molecular dynamics simulations to analyze how nematic-paranematic interfaces behave under shear, revealing interface broadening, shear banding, and flow symmetry breaking, and constructs a nonequilibrium phase diagram.

Contribution

It provides detailed insights into the behavior of nematic interfaces under shear, including interface broadening, flow symmetry breaking, and phase stability, using large-scale molecular dynamics simulations.

Findings

Interfacial width increases under shear.

Shear banding causes inhomogeneous strain distribution.

Flow symmetry breaking occurs in the vorticity direction.

Abstract

We present a large-scale molecular dynamics study of nematic-paranematic interfaces under shear. We use a model of soft repulsive ellipsoidal particles with well-known equilibrium properties, and consider interfaces which are oriented normal to the direction of the shear gradient (common stress case). The director at the interface is oriented parallel to the interface (planar). A fixed average shear rate is imposed with Lees-Edwards boundary conditions, and the heat is dissipated with a profile-unbiased thermostat. First we study the properties of the interface at one particular shear rate in detail. The local interfacial profiles and the capillary wave fluctuations of the interfaces are calculated and compared with those of the corresponding equilibrium interface. Under shear, the interfacial width broadens and the capillary wave amplitudes at large wavelengths increase. The strain is distributed inhomogeneously in the system (shear banding), the local shear rate in the nematic region being distinctly higher than in the paranematic region. Surprisingly, we also observe (symmetry breaking) flow in the {\em vorticity} direction, with opposite direction in the nematic and the paranematic state. Finally, we investigate the stability of the interface for other shear rates and construct a nonequilibrium phase diagram.