Local biaxiality in cholesteric liquid crystals from the surface interaction model

Area of Science:

• Materials Science
• Physical Chemistry
• Soft Matter Physics

Background:

• Local biaxiality is a key feature of orientational order in twisted nematic and cholesteric liquid crystal phases.
• Understanding this biaxiality is crucial for characterizing liquid crystal behavior and their applications.
• Previous models often rely on approximations, necessitating a more comprehensive approach.

Purpose of the Study:

• To develop a tool for parameterizing the mean-field orientational potential based on surface interactions.
• To investigate the dependence of orientational order parameters on the pitch of the liquid crystal phase.
• To analyze the biaxiality parameter B and its sensitivity to molecular geometry in twisted phases.

Main Methods:

• Modeling the mean-field orientational potential using a surface interaction model.
• Developing a tool for complete potential parameterization for diverse molecular structures.
• Applying the method to various molecular geometries (ellipsoidal, conical, lath-shaped, propeller-like) and their enantiomers.
• Evaluating the dependence of second-rank orientational order parameters on phase pitch.

Main Results:

• The study successfully parameterized the mean-field orientational potential for general molecular structures.
• The long-pitch approximation commonly used for modeling molecular order was recovered.
• Calculations demonstrated the dependence of orientational order parameters on the phase pitch for different molecular shapes.
• The biaxiality parameter B was shown to be sensitive to molecular geometry, impacting NMR spectral analysis.

Conclusions:

• The developed tool provides a comprehensive method for analyzing local biaxiality in twisted liquid crystals.
• Molecular geometry significantly influences the orientational order and the biaxiality parameter B.
• The findings offer insights into interpreting experimental data, particularly from deuterium NMR (2H-NMR) spectroscopy, for twisted liquid crystal systems.