Pattern-induced anchoring transitions in nematic liquid crystals

Area of Science:

• Soft Matter Physics
• Materials Science
• Surface Science

Background:

• Nematic liquid crystals (NLCs) exhibit unique optical and electrical properties.
• Substrate patterning is crucial for controlling NLC alignment in devices.
• Homeotropic anchoring describes NLC molecules aligning perpendicular to a surface.

Purpose of the Study:

• To investigate the behavior of nematic liquid crystals interacting with patterned substrates.
• To analyze the influence of substrate geometry (sawtooth, crenellated, sinusoidal) on NLC anchoring.
• To understand the role of topological defects in NLC texture transitions.

Main Methods:

• Utilized the modified Frank-Oseen formalism for theoretical analysis.
• Modeled substrates as periodic arrays of parallel grooves with defined cross-sections.
• Considered homeotropic anchoring conditions favoring perpendicular alignment.

Main Results:

• Observed distinct nematic textures and far-field orientations dependent on substrate patterns.
• Identified transitions between homeotropic, planar, and oblique anchoring states.
• Found that topological defects near the substrate are linked to anchoring transitions.

Conclusions:

• Substrate periodicity significantly larger than extrapolation length leads to defect-mediated transitions.
• Sawtooth and sinusoidal substrates show a homeotropic to planar transition with increasing roughness.
• Crenellated substrates exhibit a complex homeotropic to oblique transition dependent on roughness and anchoring strength.