Partially Disordered Crystal Phases and Glassy Smectic Phases in Liquid Crystal Mixtures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Liquid crystals exhibit diverse mesophases crucial for advanced materials.
• Understanding phase transitions and glass formation in liquid crystalline mixtures is vital for developing new functional materials.
• The interplay between molecular structure and macroscopic properties in liquid crystals remains an active area of research.

Purpose of the Study:

• To investigate the phase behavior of MHPOBC and 3F5FPhF6 mixtures.
• To analyze the impact of varying molar ratios on the formation of smectic A*, C*, and C_A* phases.
• To study the vitrification and crystallization phenomena in these mixtures and characterize their relaxation dynamics.

Main Methods:

• Preparation and investigation of three liquid crystalline mixtures (MIX5FF6-1, MIX5FF6-2, MIX5FF6-3) with varying molar ratios of MHPOBC and 3F5FPhF6.
• Observation of liquid crystalline phases using [mention technique if available, otherwise omit].
• Broadband dielectric spectroscopy to study relaxation times in smectic and crystal phases.

Main Results:

• All mixtures exhibited smectic A*, smectic C*, and smectic C_A* phases.
• The hexatic smectic X_A* phase present in pure MHPOBC disappeared with increasing 3F5FPhF6 concentration.
• Vitrification of smectic C_A* was observed in the equimolar mixture, with comparable glass transition temperature and fragility index to pure 3F5FPhF6.
• Partial crystallization to disordered crystal phases occurred in mixtures with lower 3F5FPhF6 fractions upon cooling.

Conclusions:

• The addition of 3F5FPhF6 significantly alters the phase behavior of MHPOBC, suppressing the hexatic smectic X_A* phase and promoting vitrification.
• Dielectric spectroscopy revealed distinct relaxation dynamics in the supercooled smectic X_A* and smectic C_A* phases, analyzed using established models.
• The study provides insights into the structure-property relationships in binary liquid crystal systems, relevant for designing materials with tailored thermal and dielectric properties.