arXiv subjects

Dennis Kwaria

Publications and source records attributed to Dennis Kwaria.

4 recordsLinked to original sources

arXiv2026

Electrically Tunable Heliconical Smectic Superstructure in Polar Fluids

The ferroelectric nematic (NF) phase and related polar liquid-crystalline phases form a new class of strongly polarized yet fluid soft matter. Well-recognized heliconical ferroelectric phases such as NTBF and SmC_P^H exist, but their electro-optic functionality in smectic systems has been largely unexplored. Here, we report a newly designed single-component achiral molecule exhibiting a hierarchical polar phase sequence: SmAF-NTBF-HEC-SmC_P^H. The key feature of the SmC_P^H phase is its ability to form a stable macroscopic orientation without any alignment layers and to enable continuous, reversible pitch modulation over a wide spectral range at ultralow electric fields, approximately one-third of those required for conventional heliconical nematics. The system exhibits characteristic electro-optic properties in the sub-kilohertz range, differentiating it from heliconical materials controlled by dielectric-elastic balance at higher frequencies. In addition, the SmC_P^H phase's polar heliconical smectic structure facilitates enhanced second-harmonic generation via favorable phase matching, thereby establishing a simple and robust platform for low-voltage photonic applications.

cond-mat.soft↗

arXiv2025

Three-Dimensional Hieratical Twists in Polar Fluids: Chirality Regulation by Ultra-Low Electric Field

Recently discovered helical polar fluid adopts a spontaneous chiral symmetry breaking (CSB) driven by polarization escape and conformational chirality. Ferroelectric nematic and smectic phases are intrinsically chiral in the ground state and can be stabilized in an extrinsic twisted configuration through surface anchoring. Herein, we introduce extrinsic CSB as a novel technique in chiral engineering. To demonstrate this concept, we constructed the extrinsic structure of a helielectric conical mesophase (HEC)-three-dimensional chiral system. Considering the challenges of controlling chirality at the macroscopic scale owing to magnetic fields, light, and fluid vortex motion, the proposed three-dimensional chiral system enables chirality (twist) modulation through an ultralow electric field, thereby controlling unique diffraction pattern and circular polarized light-switching capabilities.

physics.optics↗

arXiv2025

Spontaneous Twist of Ferroelectric Smectic Blocks in Polar Fluids

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.

cond-mat.soft↗

arXiv2024

Emergent Ferroelectric Nematic and Heliconical Ferroelectric Nematic States in an Achiral "Straight" Polar Rod Mesogen

Ferroelectric nematic liquid crystals (NFLCs) are distinguished by their remarkable polarization characteristics and diverse physical phenomena, sparking significant interest and excitement within the scientific community. To date, over 150 NFLC molecules have been developed; however, there are no reports regarding straight linear polar molecules with a parallel alignment of the permanent dipole moment and the molecular axis. The straight polar mesogen nBOE exhibited an enantiotropic NF phase with a wide temperature window (up to 100 K) despite having a longer alkyl chain (up to n = 6) than the critical alkyl chain length of conventional models. Interestingly, nBOE with a medium length alkyl chain displayed an exotic phase sequence of NF-HCNF-SmCF during the elimination of positional displacement among adjacent molecules. Furthermore, we demonstrate the reflective color modulation of the HCNFLC over the entire VIS-NIR spectral regime by ultralow E-field (up to 0.14 V um^-1).

cond-mat.mtrl-sci↗