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Flexoelectric properties – the effective flexoelectric coefficient and flexoelectric polarization – are investigated for a bimesogenic liquid crystal CBC11CB with a twist bend nematic phase (Ntb). Results show that the effective flexoelectric coefficient is at least two times higher than that for bimesogens that do not exhibit the Ntb phase. The flexoelectric polarization for the Ntb phase is also two times greater than that in the nematic phase. In a temperature gradient cell, we observe surprisingly a new phenomenon, in the bimesogens CBC7CB and CBC9CB and their mixtures with 5CB, of periodic self-assembly in the N phase close to the N–Ntb phase transition temperature. This phenomenon is reminiscent of the self-deformation and spontaneous chirality that appear in the system. [ABSTRACT FROM AUTHOR]

The fundamental parameter of the uniaxial liquid crystalline state that governs nearly all of its physical properties is the primary orientational order parameter (S) for the long axes of molecules with respect to the director. The biaxial liquid crystals (LCs) possess biaxial order parameters depending on the phase symmetry of the system. In this paper we show that in the first approximation a biaxial orthogonal smectic phase can be described by two primary order parameters: S for the long axes and C for the ordering of the short axes of molecules. The temperature dependencies of 5 and C are obtained by the Haller's extrapolation technique through measurements of the optical birefringence and biaxiality on a nontilted polar antiferroelectric (Sm-APA) phase of a homologous series of LCs built from the bent-core achiral molecules. For such a biaxial smectic phase both S and C, particularly the temperature dependency of the latter, are being experimentally determined. Results show that 5 in the orthogonal smectic phase composed of bent cores is higher than in Sm-A calamatic LCs and C is also significantly large. [ABSTRACT FROM AUTHOR]

Non-polar biaxial SmAb mesophase was observed in a 4-cyanoresorcinol bisbenzoate with two terephthalate–based wings bent-core (BC) compound (PAL 29) having 16 carbon atoms in the terminal alkyl chain. Electro-optic and dielectric properties of this phase have been studied in detail. The biaxial SmAb phase transforms to ferroelectric state by the application of higher voltage. The field dependent biaxiality is very small and the polarizing microscopic texture observations support the corresponding measurements. Dielectric study exhibits two relaxation processes in the polar phase temperature region and one in the apolar biaxial SmAb phase. [ABSTRACT FROM PUBLISHER]

The important parameter of the mesogens which governs nearly all fascinating physical properties is its order parameter. In the biaxial liquid crystals (LCs), there are two order parameters: primary (long axis) and secondary (short axis). The secondary orientational order parameter (η) of an achiral bent core (BC) LC material with terminal alkyl chain length 8 was estimated from the temperature dependent field induced biaxiality measurements in SmAPA phase for the first time. The Haller's extrapolation technique is used for the estimation of η as it can directly apply to biaxiality measurements rather than to refractive indices. [ABSTRACT FROM PUBLISHER]

We present the properties of different achiral orthogonal polar smectic phases observed in a homologous series of bent-core molecular compounds. The macroscopically uniaxial SmAPR phase transforms to biaxial state by the application of higher electric fields and biaxial SmAPA phase undergoes biaxial-uniaxial-biaxial texture transformation with increasing electric fields, i.e., initial antiferroelectric structure transforms into ferroelectric state under higher electric fields and it shows three different optically distinguishable states. The SmAPAR phase shows an entirely different response compared to other polar smectic phases under study. The dielectric measurements in the SmAPAR phase is the evidence of antiferroelectric behavior of uniaxial state. The polarizing microscopy texture observation supports the corresponding biaxiality measurements. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

The mesomorphic properties of an achiral bent-core liquid crystal derived from 4-cyanoresorcinol are studied by polarizing optical microscopy, x-ray diffraction, and second harmonic electro-optic response. It shows a novel sequence of four nontilted or orthogonal smectic phases on cooling: SmA-SmAPR-SmAPX-SmAPA. Here SmAPX is the new orthogonal polar uniaxial smectic phase. The electric-field-induced transformations in the SmAPX phase give rise to two biaxial states separated by a uniaxial one. The second harmonic electro-optic response in this phase is interpreted in terms of the polar interaction with the electric field. A comparison of the experimental results with the next-nearest-neighbor model for the structure of the SmAPX phase shows it to be an SmAPα phase. [ABSTRACT FROM AUTHOR]

We report the observation of biaxial nematic phase in a bent-core molecular system in which the biaxiality exists on a microscopic scale using polarizing microscopy, electro-optics and dielectric spectroscopy. An application of electric field induces a macroscopic biaxiality and therefore electro-optic switching. The observed electro-optic switching is explained in terms of the interaction of the ferroelectric clusters with the electric field. Dielectric spectra of the sample shows existence of low-frequency collective processes related to the microscopic polar clusters. The dielectric constant changes its sign from positive to negative and again to positive values. [ABSTRACT FROM AUTHOR]

We report the structural and relaxation investigations of an achiral bent-core compound in SmAPA phase. The studied material undergoes transition from one biaxial state to the other via a uniaxial state under electric field. These transformations are explained as successive transition from antiferroelectric to ferroelectric states, where, the intermediate uniaxial state has the molecular secondary directors in the neighbouring smectic layers perpendicular to each other. We also found that near SmAPR to SmAPA phase transition the second harmonic electro-optic response, induced polarization, and the dielectric behaviour hint softening behaviour in the material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Correction for ‘Flexoelectric behavior of bimesogenic liquid crystals in the nematic phase – observation of a new self-assembly pattern at the twist-bend nematic and the nematic interface’ by R. Balachandran et al., J. Mater. Chem. C, 2014, 2, 8179–8184. [ABSTRACT FROM AUTHOR]

The effects of temperature and applied voltage on the pyroelectric properties of an antiferroelectric liquid crystal are given. It has been found that the pyroelectric signal depends strongly on the bias voltage across the sample. The pyroelectric signal behaviour is interpreted with the aid of spontaneous polarization data and good agreement is found between the results from the pyroelectric and polarization techniques. The spontaneous polarization of the sample exhibits the temperature- and field-induced `Devil's staircase' behaviour, as predicted by the Ising model.