Molecular model for nematic, smectic-A, and smectic-C liquid crystals.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Physical Chemistry

Background:

• Liquid crystals exhibit diverse mesophases, including isotropic, nematic, smectic-A, and smectic-C.
• Understanding the molecular interactions governing phase transitions is crucial for materials design.
• Existing models like the McMillan model provide a basis for analyzing these transitions.

Purpose of the Study:

• To develop and analyze a molecular model for liquid crystal phase transitions.
• To describe the isotropic, nematic, smectic-A, and smectic-C phases and their interconversions.
• To investigate the role of molecular shape and interactions in determining phase behavior.

Main Methods:

• Analysis of a molecular model incorporating a pair potential with cylindrical symmetry.
• Inclusion of a biquadratic pair potential to favor molecular tilt within smectic layers.
• Comparison of the model's phase diagram with the McMillan molecular model.

Main Results:

• The model successfully describes phase transitions between isotropic, nematic, smectic-A, and smectic-C phases.
• The phase diagram for the first three phases resembles that of the McMillan model.
• A continuous phase transition line separates the smectic-C and nematic phases, characterized by a non-zero tilt angle.

Conclusions:

• The proposed molecular model accurately captures key liquid crystal phase behaviors.
• The biquadratic potential effectively models the molecular tilt in smectic phases.
• The tilt angle continuously vanishes at the smectic-C to smectic-A phase transition line.