Biaxial nematic phase in bent-core thermotropic mesogens

Area of Science:

• Materials Science
• Condensed Matter Physics
• Crystallography

Background:

• Theoretical models predicted a biaxial nematic phase with D(2h) symmetry.
• This phase requires simultaneous alignment of molecular long and short transverse axes with two orthogonal directors.
• Bent-core mesogens are candidates for exhibiting such complex liquid crystalline phases.

Purpose of the Study:

• To experimentally investigate the existence of a biaxial nematic phase in rigid bent-core mesogens.
• To characterize the structural properties of this phase using X-ray diffraction.
• To validate theoretical predictions and computational models for bent-core liquid crystals.

Main Methods:

• Synthesis and characterization of three rigid bent-core mesogens.
• Low-angle X-ray diffraction measurements on the synthesized mesogens in their nematic phases.
• Ab initio calculations incorporating molecular shape and positional correlations.

Main Results:

• Unique low-angle X-ray diffraction patterns indicative of biaxiality were observed.
• The experimental diffraction data clearly revealed the presence of the biaxial nematic phase.
• Ab initio calculations successfully reproduced the observed X-ray diffraction patterns.

Conclusions:

• The experimental results confirm the existence of the predicted biaxial nematic phase in bent-core mesogens.
• The study validates the use of X-ray diffraction for identifying and characterizing molecular biaxiality in liquid crystals.
• Computational modeling, including molecular shape, is effective in simulating and understanding these complex phases.