Vortex Lattices in Active Nematics with Periodic Obstacle Arrays

TL;DR

This paper models active nematic systems with periodic obstacles, revealing a tunable vortex lattice state influenced by activity level and obstacle spacing, with potential transitions to turbulence.

Contribution

It introduces a numerical model showing how obstacle arrays can control vortex lattice formation and defect dynamics in active nematics.

Findings

Vortex lattice emerges with increased activity.

Lattice can be tuned from ferromagnetic to antiferromagnetic.

Various states including turbulence are mapped.

Abstract

We numerically model a two-dimensional active nematic confined by a periodic array of fixed obstacles. Even in the passive nematic, the appearance of topological defects is unavoidable due to planar anchoring by the obstacle surfaces. We show that a vortex lattice state emerges as activity is increased, and that this lattice may be tuned from ``ferromagnetic'' to ``antiferromagnetic'' by varying the gap size between obstacles. We map the rich variety of states exhibited by the system as a function of distance between obstacles and activity, including a pinned defect state, motile defects, the vortex lattice, and active turbulence. We demonstrate that the flows in the active turbulent phase can be tuned by the presence of obstacles, and explore the effects of a frustrated lattice geometry on the vortex lattice phase.