Defect Spirograph: Dynamical Behavior of Defects in Spatially Patterned Active Nematics

TL;DR

This paper investigates how topological defects in active nematic liquid crystals behave under activity gradients, revealing various dynamic modes and potential for microfluidic applications.

Contribution

It introduces a phase diagram describing defect dynamics in active nematics under activity and friction variations, supported by continuum simulations.

Findings

Identified distinct defect dynamical modes such as immobile, rotating, bouncing, dancing, and irregular states.

Developed a phase diagram linking activity and friction to defect behavior.

Suggested potential for creating synchronized defect arrays for microfluidic devices.

Abstract

Topological defects in active liquid crystals can be confined by introducing gradients of activity. Here, we examine the dynamical behavior of two defects confined by a sharp gradient of activity that separates an active circular region and a surrounding passive nematic material. Continuum simulations are used to explain how the interplay among energy injection into the system, hydrodynamic interactions, and frictional forces governs the dynamics of topologically required self-propelling $+1/2$ defects. Our findings are rationalized in terms of a phase diagram for the dynamical response of defects in terms of activity and frictional damping strength. Different regions of the underlying phase diagram correspond to distinct dynamical modes, namely immobile defects (ID), steady rotation of defects (SR), bouncing defects (TB), bouncing-cruising defects (BC), dancing defects (DA), and multiple defects with irregular dynamics (MD). These dynamic states raise the prospect of generating synchronized defect arrays for microfluidic applications.