Flow around topological defects in active nematic films.

Area of Science:

• Soft Matter Physics
• Hydrodynamics
• Active Matter Systems

Background:

• Active nematic films exhibit complex flow patterns driven by self-propelled constituent elements.
• Defects in these systems significantly influence fluid dynamics and emergent behaviors.
• Dissipation mechanisms, including viscous and frictional damping, play a crucial role in modulating system dynamics.

Purpose of the Study:

• To investigate the active flow dynamics around isolated defects in a nematic film.
• To analyze the self-propulsion velocity of topological defects under varying dissipation conditions.
• To understand the interplay between viscous dissipation, frictional damping, and hydrodynamic screening effects.

Main Methods:

• Theoretical modeling of active nematic hydrodynamics.
• Analysis of defect-induced flow fields and vorticity.
• Mathematical formulation of dissipation mechanisms and their impact on defect motion.

Main Results:

• The size of shear vorticity around an isolated defect is dictated by system size in the absence of screening.
• Frictional damping leads to vorticity field decay beyond the hydrodynamic dissipation length.
• Defect self-propulsion velocity exhibits a system-size dependent behavior, saturating in large systems or at high friction.

Conclusions:

• The hydrodynamic dissipation length is a key parameter controlling flow screening and defect behavior.
• Both viscous and frictional dissipation are critical in determining the dynamics of active nematic defects.
• The self-propulsion of defects is tunable through system geometry and substrate friction.