A Fluid Liquid‐Crystal Material with Highly Polar Order

Abstract

An anomalously large dielectric permittivity of ≈10 is found in the mesophase temperature range (MP phase) wherein high fluidity is observed for a liquid-crystal compound having a 1,3-dioxane unit in the mesogenic core (DIO). In this temperature range, no sharp X-ray diffraction peak is observed at both small and wide Bragg angles, similar to that for a nematic phase; however, an inhomogeneous sandy texture or broken Schlieren one is observed via polarizing optical microscopy, unlike that for a conventional nematic phase. DIO exhibits polarization switching with a large polarization value, i.e., P = 4.4 µC cm , and a parallelogram-shaped polarization-electric field hysteresis loop in the MP phase. The inhomogeneously aligned DIO in the absence of an electric field adopts a uniform orientation along an applied electric field when field-induced polarization switching occurs. Furthermore, sufficiently larger second-harmonic generation is observed for DIO in the MP phase. Second-harmonic-generation interferometry clearly shows that the sense of polarization is inverted when the +/- sign of the applied electric field in MP is reversed. These results suggest that a unidirectional, ferroelectric-like parallel polar arrangement of the molecules is generated along the director in the MP phase.

First-principles experimental demonstration of ferroelectricity in a thermotropic nematic liquid crystal: Polar domains and striking electro-optics

“…3C). The resulting P increases continuously from small values at the transition, saturating at low T at a value P ∼ 6 μC/cm 2 , a value comparable to the ∼4 μC/cm 2 found by Kikuchi et al in the compound DIO (29). Polarization in the N-N F transition temperature region may include pretransitional contributions in the N phase due to the divergence of e ‖ (30), but this has not yet been studied in detail.…”

“…In 2017, Mandle et al (28) and Kikuchi et al (29) separately reported new LC compounds exhibiting unusual phase behavior: two distinct, fluid nematic phases separated in temperature by a weakly first-order phase transition. In both cases, the molecules were rod-shaped, with several intramolecular dipoles distributed along their length whose projections onto the molecular long axis summed to a large overall axial dipole moment of ∼10 Debye.…”

“…In both cases, the molecules were rod-shaped, with several intramolecular dipoles distributed along their length whose projections onto the molecular long axis summed to a large overall axial dipole moment of ∼10 Debye. The high-temperature phase of both mesogens was reported to be a typical nematic, but they exhibited dramatic paraelectric (30,29) and ferroelastic (30) pretransitional effects, with a dielectric constant surpassing 1,000 as the transition to the lowtemperature phase was approached. The low-temperature phase exhibited enhanced dipolar molecular associations, reported to be antiparallel in the Mandle system (28) and suggested to be parallel in the Kikuchi system, the latter being termed "ferroelectric-like" (29), giving macroscopic polar ordering in response to an applied electric field.…”

Nature‐Inspired Emerging Chiral Liquid Crystal Nanostructures: From Molecular Self‐Assembly to DNA Mesophase and Nanocolloids

“…[558][559][560][561][562][563][564][565] Supramolecular ferroelectrics with high spontaneous polarization and fast electro-optic switching attributes have been demonstrated in diverse liquid crystalline systems such as thermotropic and lytropic chiral smectic phases as well as ferroelectric columnar mesophases. [566][567][568][569][570] Ferroelectric LCs could be strategic materials for future ultrafast switching devices such as optical computing, optical recognition, spatial light modulators, and telecommunications switching. [571][572][573] The arbitrary control over the wavefront of light reflected from chiral LC superstructures has been achieved through appropriately manipulating the spatial distribution of the helix phase, which is expected to open unprecedented paths toward the development of next-generation advanced optical elements for spin-orbit photonic technologies.…”

Orientational order in the splay nematic ground state

“…It is possible that the 'MP' phase reported by Kikuchi et al is another example of the splay nematic phase. 14 Barbero and Lelidis recently discussed the possibility of periodic modulated splay-nematic phases that results from a negative value of K 11 . 15 The proposed structure of the N S phase is polar, biaxial and antiferroelectric and therefore of significant interest for electrooptic devices.…”