Binary mixtures of liquid crystalline compounds with a reentrant smectic-A* phase

Area of Science:

• Materials Science
• Condensed Matter Physics
• Crystallography

Background:

• Chiral liquid crystals exhibit complex phase behaviors, including ferroelectric and paraelectric smectic phases.
• The reentrant Smectic A* (SmA*(RE)) phase, appearing below the ferroelectric SmC* phase, presents unique characteristics.
• Understanding phase transitions and stabilization mechanisms in liquid crystal mixtures is crucial for advanced material applications.

Purpose of the Study:

• To investigate the stabilization of the reentrant Smectic A* (SmA*(RE)) phase in binary mixtures of chiral liquid crystalline homologs.
• To characterize the phase behavior and transitions in mixtures of 9ZBL with 8ZBL and 10ZBL.
• To elucidate the relationship and distinguish the nature of the SmA* and SmA*(RE*) phases.

Main Methods:

• Synthesis and study of binary mixtures of chiral liquid crystalline compounds (9ZBL, 8ZBL, 10ZBL).
• X-ray diffraction studies to analyze layer spacing and structural changes.
• Dielectric spectroscopy, polarization, and tilt angle measurements for phase characterization.

Main Results:

• The reentrant SmA*(RE*) phase was observed in 9ZBL-10ZBL mixtures across all concentrations.
• In 9ZBL-8ZBL mixtures, small additions of 8ZBL (up to 0.5 mol%) suppressed the SmC* phase.
• An anomaly in layer spacing and reduced X-ray intensity in 9ZBL-8ZBL mixtures (up to 20 mol% 8ZBL) indicated a boundary between SmA* and SmA*(RE*) phases.

Conclusions:

• The study successfully stabilized the reentrant Smectic A* (SmA*(RE)) phase in binary liquid crystal mixtures.
• The observed anomaly confirms the distinct nature of the SmA* and SmA*(RE*) phases, providing evidence for a phase boundary.
• These findings contribute to a deeper understanding of phase complexity in chiral liquid crystalline systems.