Lattice Boltzmann simulations of spontaneous flow in active liquid crystals: the role of boundary conditions

TL;DR

This paper uses lattice Boltzmann simulations to explore how boundary conditions influence spontaneous flow in active liquid crystals, revealing conditions that induce flow regardless of activity level and others that require a threshold.

Contribution

It demonstrates how boundary conditions affect spontaneous flow in active liquid crystals, providing new insights into their hydrodynamics and steady-state behavior.

Findings

Active liquid crystals can sustain spontaneous flow in steady state.

Conflicting boundary conditions induce flow at any activity level.

Unfrustrated boundaries require activity above a critical threshold for flow.

Abstract

Active liquid crystals or active gels are soft materials which can be physically realised e.g. by preparing a solution of cytoskeletal filaments interacting with molecular motors. We study the hydrodynamics of an active liquid crystal in a slab-like geometry with various boundary conditions, by solving numerically its equations of motion via lattice Boltzmann simulations. In all cases we find that active liquid crystals can sustain spontaneous flow in steady state contrarily to their passive counterparts, and in agreement with recent theoretical predictions. We further find that conflicting anchoring conditions at the boundaries lead to spontaneous flow for any value of the 'activity' parameter, while with unfrustrated anchoring at all boundaries spontaneous flow only occurs when the activity exceeds a critical threshold. We finally discuss the dynamic pathway leading to steady state in a few selected cases.