Liquid Crystal Display Modes in a Nontilted Bent-Core Biaxial Smectic Liquid Crystal

Liquid crystal display (LCD) modes associated with the rotation of the secondary director in nontilted, biaxial smectic phase of an achiral bent-core compound are demonstrated. For LCDs, we find that at least four display modes are possible using SmAPA phase of the studied material, in which the minor directors in adjacent layers are aligned antiferroelectrically. The advantages of these modes include low driving field (1–2 V/ µm), high contrast ratio 1000:1, relatively fast switching time of 0.5 ms and continuous gray scale. The molecular short axis or the polar axis in a negative dielectric, biaxial material is oriented by the in-plane electric field by a combination dielectric biaxiality and polarity at low electric fields and polarity at higher fields

A fast linear electro-optical effect in a non-chiral bent-core liquid crystal

We report the observation of an electro-optical effect for a linear rotation of the optical axis as function of the electric field in an achiral tilted bent-core liquid crystalline compound, in which 4-cyanoresorcinol bisbenzoate core is symmetrically terminated by long linear alkyl chains (n =16) on both ends. The linear electro-optic effect observed in this material is similar to the deformed helical ferroelectric liquid crystal (DHFLC) effect reported previously in a FLC material except that dimensions of the helical pitch differ by two orders of magnitude. In the chiral systems, the helical pitch usually lies on the scale of sub-optical wavelength, ~0.3 m depending on the material and temperature, whereas in the achiral system, the pitch lies on the nm scale. The DHFLC mode shows fast, analog switching due to a gradual distortion of the uniform helical structure by the electric field; the switching speed is faster than for the chiral systems. In contrast to the chiral FLCs, achiral liquid crystalline materials appear as better candidates for applications in displays and the photonic technologies

Electric field induced biaxiality and the electro-optic effect in a bent-core nematic liquid crystal

We report the observation of a biaxial nematic phase in a bent-core molecular system using polarizing microscopy, electro-optics, and dielectric spectroscopy, where we find that the biaxiality exists on a microscopic scale. An application of electric field induces a macroscopic biaxiality and in consequence gives rise to electro-optic switching. This electro-optic effect shows significant potential in applications for displays due to its fast high-contrast response. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field

Formation of a Double Diamond Cubic Phase by Thermotropic Liquid Crystalline Self-Assembly of Bundled Bolaamphiphiles

A quaternary amphiphile with swallow-tail side groups displays a new bicontinuous thermotropic cubic phase with symmetry Pn3‾ m and formed by two interpenetrating networks where cylindrical segments are linked by H bonds at tetrahedral junctions. Each network segment contains two bundles, each containing 12 rod-like mesogens, lying along the segment axis. This assembly leads to the first thermotropic structure of the "double diamond" type. A quantitative geometric model is proposed to explain the occurrence of this rare phase

Occurrence of Five Different Orthogonal Smectic Phases in a Bent-Core (BC) Liquid Crystal

Five orthogonal smectic phases (Sm-A, Sm-Ab, Sm-APR, Sm-APAR, and Sm-APA) were observed in a 4-cyanoresorcinol bisbenzoate with twoterephthalate–based wings achiral bent-core(BC) compound. The phase behavior was investigated by polarising optical microscopy, second harmonic electro-optic response(EO2) and dielectric spectroscopy. The field dependent biaxiality of polar and non-polar Sm-A phases was studied. It is obviously of enormous scientific significance and practical interest to find five different orthogonal smectic phases in a low molecular weight bent-core (BC) compound at relatively low temperatures

Structure and Polymorphism of Biaxial Bent-Core Smectic Liquid Crystal

The mesomorphic properties of a homologous series of achiral bent-core compounds are studied by polarizing optical microscopy, electro-optics and polarization measurements. Induction of a new orthogonal smectic phases with the increase of alkyl side chain length was observed. One of the compounds exhibits a unique phase transition between four non-tilted smectic phases (SmAPA–SmAPAR-SmAPR-SmA). The uniaxial but antiferroelectric nature of SmAPAR phase was confirmed by POM, current response, the 2nd harmonic electro-optic response and polarization measurements. The structure of SmAPAR phase was studied theoretically by Next-Nearest-Neighbor model and was identified as SmAPα

Chirality induction through nano-phase separation: Alternating network gyroid (I4132) phase by thermotropic self-assembly of X-shaped bolapolyphiles

The single gyroid phase as well as the alternating double network gyroid, composed of two alternating single gyroid networks, hold a significant place in ordered nanoscale morphologies for their potential applications as photonic crystals, metamaterials and templates for porous ceramics and metals. Here we report the first alternating network cubic liquid crystals. They form through self‐assembly of X‐shaped polyphiles, where the glycerol‐capped terphenyl rods lie on the gyroid surface while the semiperfluorinated and aliphatic side‐chains fill their respective separate channel networks. This new self‐assembly mode can be considered as a two‐color symmetry‐broken double gyroid morphology, providing a tailored way to fabricate novel chiral structures with sub‐10 nm periodicities using achiral compounds