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Driven topological transitions in active nematic films.

David P Rivas1, Tyler N Shendruk2, Robert R Henry1

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Summary
This summary is machine-generated.

Active nematic films exhibit controllable topological defects. Applying stress can merge +1/2 defects into +1 vortices, altering flow dynamics and revealing anomalous viscoelasticity.

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Area of Science:

  • Soft Matter Physics
  • Active Matter Physics
  • Topological Defects

Background:

  • Topological properties are crucial for material behavior, especially in active materials far from equilibrium.
  • The dynamics of topological defects significantly influence the properties of active materials.

Purpose of the Study:

  • To demonstrate local manipulation of order, dynamics, and topological properties in microtubule-based active nematic films.
  • To investigate the influence of external stresses on topological defect behavior and active film hydrodynamics.

Main Methods:

  • Joint experimental and simulation study using microtubule-based active nematic films.
  • Magnetic actuation of disk-shaped colloids to create localized hydrodynamic stresses.
  • Lattice Boltzmann simulations to model film behavior and capture anomalous viscoelasticity.

Main Results:

  • Applied stresses influence the motion of +1/2 charge topological defects.
  • Sufficient stress drives the merger of two +1/2 defects into a +1 charge topological vortex.
  • Defect motion leads to ordering of vorticity and velocity, unlike passive films.
  • Topological vortex formation is linked to a rheological instability and increased flow velocities.

Conclusions:

  • Local stress application provides control over topological defects and dynamics in active nematics.
  • The study reveals the anomalous viscoelastic nature of active nematic films.
  • Lattice Boltzmann simulations effectively capture key features of the active nematic response to stress.