Annihilation of nematic point defects: pre-collision and post-collision evolution

Area of Science:

• Nematic liquid crystals
• Defect dynamics
• Soft matter physics

Background:

• Nematic liquid crystals exhibit topological defects like hedgehogs and anti-hedgehogs.
• Understanding defect interactions and annihilation is crucial for predicting material behavior.

Purpose of the Study:

• To investigate the annihilation dynamics of nematic hedgehogs and anti-hedgehogs within an infinite cylinder.
• To analyze the distinct stages of defect interaction and their resulting structures.

Main Methods:

• Utilized a semi-microscopic lattice-type model.
• Employed Brownian molecular dynamics simulations.
• Distinguished four stages: early/late pre-collision and early/late post-collision.

Main Results:

• Defect interaction is negligible for large initial separations (xi(0)d/(2R) > 1).
• Annihilation occurs within the simulation window for closer defects (xi(0)d/(2R) < 1).
• Separation scales as (t(c) - t)^(0.4+/-0.1) before collision; anisotropic media affect defect speeds.

Conclusions:

• Post-collision, a charge-less ring forms, evolving into an untwisted circular structure.
• For mu < 0.25, the ring collapses into an escaped radial structure.
• For mu > 0.25, the ring nucleates a planar polar structure with line defects.