Ordering of Oblate Hard Particles between Hybrid Penetrable Walls

Area of Science:

• Soft Matter Physics
• Materials Science
• Computational Chemistry

Background:

• Understanding molecular alignment in confined systems is crucial for liquid crystal display technology.
• Discotic liquid crystals (DLCs) exhibit unique self-assembly properties.
• Controllable wall interactions offer a method to tune molecular orientation.

Purpose of the Study:

• To investigate the alignment behavior of discotic liquid crystals confined between hybrid walls with tunable penetrability.
• To map the phase behavior of DLCs as a function of wall anchoring properties.
• To compare simulation results with theoretical predictions from density functional theory.

Main Methods:

• Monte Carlo (MC) simulations were employed to model discotic liquid crystals composed of oblate hard Gaussian overlap (HGO) particles.
• Particle-substrate interactions were designed to control wall anchoring from planar (D≈0) to homeotropic (D≈σ₀).
• Simulations explored various combinations of top and bottom substrate anchoring properties.

Main Results:

• Distinct alignment domains were identified: uniform planar (UP), uniform homeotropic (UH), and linear (Lin) transition.
• Bistable (P-Lin, H-Lin) and potentially tristable (P-H-Lin) regions were observed, wider than for prolate particles.
• Discrepancies were found between MC simulations and density functional theory (DFT) predictions, particularly for the Lin configuration.

Conclusions:

• The study demonstrates the ability to control DLC alignment through hybrid confinement.
• Onsager's second-virial approximation with Parsons-Lee rescaling shows limitations in accurately predicting DLC behavior in confinement.
• Further theoretical development is needed for accurate modeling of disc-like molecules compared to rod-like ones.