Coexistence of Defect Morphologies in Three-Dimensional Active Nematics

Area of Science:

• Soft Matter Physics
• Liquid Crystal Science
• Non-equilibrium Systems

Background:

• Active stress in nematic liquid crystals drives complex dynamic behaviors.
• Disclination lines are topological defects crucial to understanding material morphology.
• Chaotic flow introduces significant challenges in predicting defect line structures.

Purpose of the Study:

• To investigate the global impact of active stress on disclination line morphology.
• To identify and characterize length scales governing defect structures in active nematics.
• To understand the interplay between activity, defect topology, and chaotic flow.

Main Methods:

• Development of a defect detection algorithm utilizing local nematic orientation.
• Numerical simulations in a 3D periodic geometry.
• Analysis of defect line scaling and fractal dimensions.

Main Results:

• Active stress selects a crossover length scale, differentiating small defect loops from large, fractal defect lines (dimension 2).
• This length scale correlates with the average separation between defects, influenced by activity levels.
• A coexistence of regular, contractible defect loops and wrapping defect lines was observed.
• Regular defect lengths scale linearly with the active length scale, while wrapping defects show an inverse quadratic dependence.

Conclusions:

• Active stress fundamentally alters disclination line morphology in 3D active nematics.
• The identified crossover length scale is a key parameter governing defect organization.
• Defect line behavior, particularly wrapping, is strongly dependent on the active length scale and boundary conditions.