Active nematic defects in compressible and incompressible flows

Area of Science:

• Soft Matter Physics
• Active Matter Dynamics
• Nematic Liquid Crystals

Background:

• Active nematic films are complex fluids with self-propelled constituent elements.
• Their behavior is influenced by flow dynamics and constraints like compressibility.
• Understanding defect organization is key to predicting large-scale patterns.

Purpose of the Study:

• To investigate the impact of compressibility and incompressibility constraints on active nematic film dynamics.
• To analyze the stability of arch patterns under different flow conditions.
• To elucidate the resulting nematic defect ordering.

Main Methods:

• Computational simulations of active nematic films.
• Theoretical analysis of fluid dynamics and defect interactions.
• Comparison of compressible versus incompressible flow scenarios.

Main Results:

• Arch patterns are stable in compressible active nematic films.
• These arches destabilize when subjected to the incompressibility constraint.
• Compressible flows at high activity yield smecticlike patterns and global polar ordering of +1/2 defects.
• Divergence-free (incompressible) flows result in local nematic order of antialigned +1/2 defect pairs.

Conclusions:

• The compressibility constraint fundamentally alters the large-scale organization of active nematic films.
• Stable arch patterns and global polar ordering are unique to compressible active nematics.
• Incompressible active nematics exhibit localized defect ordering, consistent with prior research.