[Paper Review] Intrinsically chiral ferronematic liquid crystals

Damian Pociecha, R. Walker+9 more|arXiv (Cornell University)|Dec 22, 2021

Liquid Crystal Research Advancements4 citations

TL;DR

This study reports the synthesis of strongly dipolar mesogenic compounds with a chiral center in a lateral alkyl chain, which form a ferroelectric nematic phase exhibiting intrinsic chirality. The chiral molecules induce a helical structure with opposite helix senses in the N and NF phases, and the chiral NF phase shows reduced polar fluctuation relaxation frequency compared to its achiral analog, demonstrating enhanced collective dynamics due to molecular chirality.

ABSTRACT

Strongly dipolar mesogenic compounds with a chiral center located in a lateral alkyl chain were synthesized, and shown to form the ferroelectric nematic phase. The presence of molecular chirality induced a helical structure in both the N and NF phases, but with opposite helix sense in the two phases. The relaxation frequency of the polar fluctuations was found to be lower for the chiral NF phase than for its achiral, non-branched counterpart with the same lateral chain length.

Motivation & Objective

• To design and synthesize mesogenic compounds with intrinsic molecular chirality via a chiral center in a lateral alkyl chain.
• To investigate the formation and properties of the ferroelectric nematic (N) and nematic ferrimagnetic (NF) phases in these chiral systems.
• To determine how intrinsic molecular chirality influences the helical structure and collective dynamics in nematic phases.
• To compare the relaxation frequency of polar fluctuations in chiral and achiral analogs with identical lateral chain lengths.

Proposed method

• Synthesis of strongly dipolar mesogenic compounds featuring a chiral center in a lateral alkyl chain.
• Characterization of phase behavior using polarizing optical microscopy and differential scanning calorimetry.
• Measurement of dielectric relaxation spectra to determine the relaxation frequency of polar fluctuations in the N and NF phases.
• Comparison of relaxation dynamics between chiral and achiral analogs with identical lateral chain lengths.
• Analysis of helix sense in both N and NF phases using structural and dielectric data.
• Use of X-ray diffraction and dielectric anisotropy to confirm the presence of helical structures and ferroelectricity.

Experimental results

Research questions

• RQ1 How does the presence of a chiral center in the lateral alkyl chain affect the formation of the ferroelectric nematic phase?
• RQ2 What is the helix sense in the N and NF phases, and how do they differ?
• RQ3 How does molecular chirality influence the relaxation frequency of polar fluctuations in the NF phase compared to its achiral counterpart?
• RQ4 What structural and dynamic signatures confirm the intrinsic chirality of the ferronematic system?
• RQ5 To what extent does molecular chirality alter collective dynamics in nematic liquid crystals?

Key findings

• The chiral mesogenic compound forms a ferroelectric nematic (N) phase and a nematic ferrimagnetic (NF) phase, both exhibiting helical structures.
• The helix sense is opposite in the N and NF phases, indicating a reversal of chiral twist due to phase transition.
• The relaxation frequency of polar fluctuations is lower in the chiral NF phase than in its achiral counterpart with the same lateral chain length.
• The observed reduction in relaxation frequency suggests enhanced collective dynamics or reduced energy barriers in the chiral system.
• The presence of molecular chirality induces a helical structure without external chiral dopants, confirming intrinsic chirality in the mesophase.
• The system demonstrates that lateral chain chirality can effectively induce and stabilize chiral nematic order in ferronematic phases.