Spontaneous Twist of Ferroelectric Smectic Blocks in Polar Fluids

Abstract

In soft matter, the polar orientational order of molecules can facilitate the coexistence of structural chirality and ferroelectricity. The ferroelectric nematic (N_F) 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, two types of achiral molecules (BOE-NO₂ and DIOLT) are reported that possess different molecular structures but exhibit a N_F–ferroelectric smectic phase sequence. It is demonstrated that the chiral ground state of N_F 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.