Spontaneous Twist of Ferroelectric Smectic Blocks in Polar Fluids

Area of Science:

• Soft matter physics
• Materials science
• Molecular physics

Background:

• Polar orientational order in soft matter can lead to coexisting structural chirality and ferroelectricity.
• The ferroelectric nematic (N_F) phase, formed by achiral calamitic molecules with large dipole moments, is a key model for spontaneous structural chirality.
• Depolarization effects in the N_F phase induce a helical twist in polarization, creating a chiral ground state.

Purpose of the Study:

• To investigate the emergence and inheritance of structural chirality in ferroelectric liquid crystal phases.
• To explore the relationship between molecular structure, dipole moments, and the formation of chiral states in ferroelectric nematic and smectic phases.
• To report on two novel achiral molecules, BOE-NO₂ and DIOLT, exhibiting a N_F-ferroelectric smectic phase sequence.

Main Methods:

• Synthesis and characterization of achiral molecules BOE-NO₂ and DIOLT.
• Phase behavior analysis of the synthesized molecules.
• Investigation of the structural and polar properties of the ferroelectric nematic and smectic phases.

Main Results:

• Both BOE-NO₂ and DIOLT exhibit a ferroelectric nematic to ferroelectric smectic phase transition.
• The ferroelectric smectic phase of BOE-NO₂ inherits the chiral ground state from the N_F phase.
• Larger dipole moments and steric hindrance in BOE-NO₂ promote the formation of twisted polar smectic blocks.

Conclusions:

• The chiral ground state of the ferroelectric nematic phase can be successfully transferred to ferroelectric smectic phases.
• Molecular design, including dipole moment and steric factors, is crucial for controlling chirality in ferroelectric soft matter.
• This work provides insights into the design principles for novel chiral ferroelectric materials.