Defect structures in nematic liquid crystals around charged particles

Area of Science:

• Materials Science
• Condensed Matter Physics
• Soft Matter Physics

Background:

• Nematic liquid crystals exhibit complex behavior around impurities.
• Charged particles introduce electrostatic interactions that can deform the director field.
• Understanding defect formation is crucial for liquid crystal display technology and advanced materials.

Purpose of the Study:

• To numerically investigate orientation deformations in nematic liquid crystals induced by charged particles.
• To characterize novel defect structures, such as "ansa" defects.
• To analyze the influence of dielectric anisotropy and particle charge on defect formation and particle alignment.

Main Methods:

• Utilizing a Ginzburg-Landau theory framework.
• Implementing numerical simulations with an inhomogeneous electric field.
• Analyzing director orientation and free energy minimization.

Main Results:

• Saturn-ring defects are observed for positive dielectric anisotropy (ε₁ > 0).
• Novel "ansa" defects (disclination lines) appear for negative dielectric anisotropy (ε₁ < 0).
• Oppositely charged particle pairs align parallel (ε₁ > 0) or perpendicular (ε₁ < 0) to the background director; identically charged pairs show reversed preferences.
• Competition between charge-induced and short-range anchoring is examined, with long-range electrostatics dominating far from the surface.

Conclusions:

• Charged particles induce distinct defect structures in nematic liquid crystals based on dielectric anisotropy.
• The alignment of charged particle pairs is dictated by electrostatic interactions and dielectric properties.
• Electrostatic interactions play a significant role in director orientation, especially in competition with surface anchoring effects.