Tilt order parameters, polarity, and inversion phenomena in smectic liquid crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Smectic liquid crystals exhibit complex phase transitions, notably from the smectic-A to smectic-C phase.
• Understanding the molecular basis of these transitions is crucial for developing advanced materials.
• Chiral smectic-C* phases are known for exhibiting spontaneous polarization and unique optical properties.

Purpose of the Study:

• To formulate order parameters for the smectic-A to smectic-C phase transition based on molecular symmetry.
• To investigate the origin of indigenous polarity in smectic-C phases.
• To develop a phenomenological theory explaining experimental observations in chiral smectic-C* materials.

Main Methods:

• Formulation of order parameters derived from molecular symmetry and structure.
• Application of Landau expansion theory using tilt and polar order parameters.
• Analysis of the coupling between order parameters to explain experimental phenomena.

Main Results:

• Identified multiple tilt and polar order parameters arising from molecular ordering in the smectic-C phase.
• Established that indigenous polarity is a key factor in spontaneous polarization, independent of chirality.
• Developed a model predicting sign inversions in spontaneous polarization and helical pitch.

Conclusions:

• The proposed phenomenological theory accurately describes the smectic-A to smectic-C phase transition.
• The theory provides a molecular interpretation for inversion phenomena observed in chiral smectic-C* materials.
• This work enhances the understanding of structure-property relationships in liquid crystals.