Spontaneous Twist of Ferroelectric Smectic Blocks in Polar Fluids

TL;DR

This paper reports the discovery of spontaneous twist in ferroelectric smectic blocks within polar fluids, showing how achiral molecules can exhibit chiral ferroelectric phases due to molecular structure and dipole interactions.

Contribution

It introduces two new achiral molecules with ferroelectric smectic phases, demonstrating inherited chirality and spontaneous twisting in these structures.

Findings

Achiral molecules can exhibit chiral ferroelectric smectic phases.

Molecular structure and dipole moments influence twist formation.

Spontaneous twist observed in specific ferroelectric smectic phases.

Abstract

In soft matter, the polar orientational order of molecules can facilitate the coexistence of structural chirality and ferroelectricity. The ferroelectric nematic (NF) state, exhibited by achiral calamitic molecules with large dipole moments, serves as an ideal model for the emergence of spontaneous structural chirality. This chiral ground state arises from a left- or right-handed twist of polarization due to depolarization effects. In contrast, the ferroelectric smectic state, characterized by a polar lamellar structure with lower symmetry, experiences significantly higher energy associated with layer-twisting deformations and the formation of domain walls, thus avoiding a continuously twisted layered structure. In this study, we develop two types of achiral molecules (BOE-NO2 and DIOLT) that possess different molecular structure but exhibit a NF-ferroelectric smectic phase sequence. We demonstrate that the chiral ground state of NF is inherited in the ferroelectric smectic phases of BOE-NO2, which features larger dipole moments and a steric hindrance moiety, thereby triggering the formation of the twisted polar smectic blocks.