The NTB phase in an achiral asymmetrical bent-core liquid crystal terminated with symmetric alkyl chains

The characteristics of the twist-bend nematic (NTB) phase of an achiral asymmetrical rigid bent-core liquid crystal (LC), the ends of which are terminated by symmetric alkyl chains, are reported. The nematic�nematic phase transition and its properties are studied by differential scanning calorimetry (DSC), polarising microscopy and the electro-optic techniques. Large domains of opposite handedness are observed in the absence of the external field in the NTB phase. Another set of periodic striped pattern consisting of domains with sharp boundaries is formed when a high-frequency electric field with a magnitude above its threshold is applied across a planarly aligned cell. The neighbouring domains are of opposite chirality. The temperature dependence of the heliconical angle θ0 is determined from the birefringence measurements using Haller�s extrapolation technique. This material shows lower values of the heliconical angle (~9.3° at a temperature of 155°C within the NTB phase) when compared with the previously reported dimer-based twist-bend nematic LCs (31°±3°). © 2016 Informa UK Limited, trading as Taylor & Francis Group

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

Design and Investigation of de Vries Liquid Crystals Based on 5-Phenyl-Pyrimidine and (R,R)-2,3-Epoxyhexoxy backbone.

Calamitic liquid crystals based on 5-phenyl-pyrimidine derivatives have been designed, synthesized, and characterized. The 5-phenyl pyrimidine core was functionalized with a chiral (R,R)-2,3-epoxyhexoxy chain on one side and either siloxane or perfluoro terminated chains on the opposite side. The one involving a perfluorinated chain shows SmA^{*} phase over a wide temperature range of 82 °C, whereas the siloxane analog exhibits both SmA^{*} and SmC^{*} phases over a broad range of temperatures, and a weak first-order SmA^{*}-SmC^{*} transition is observed. For the siloxane analog, the reduction factor for the layer shrinkage R (relative to its thickness at the SmA^{*}-SmC^{*} transition temperature, T_{AC}) is ∼0.373, and layer shrinkage is 1.7% at a temperature of 13 °C below the T_{AC}. This compound is considered to have de Vries smectic characteristics with the de Vries coefficient C_{deVries} of ∼0.86 on the scale of zero (maximum-layer shrinkage) to 1 (zero-layer shrinkage). A three-parameter mean-field model is introduced for the orientational distribution function (ODF) to reproduce the electro-optic properties. This model explains the experimental results and leads to the ODF, which exhibits a crossover from the sugar-loaf to diffuse-cone ODF some 3 °C above T_{AC}

On the occurrence of an interesting leafless orchid <i>Neottia listeroides</i> Lindl. In Himachal Pradesh, northwestern Himalaya, India

Field explorations in Himachal Pradesh (2002-2010) have resulted in documenting some new distributional records of orchids for the state. They exhibited a variety of life forms (epiphytes/ terrestrials/ lithophytes) and are mostly distributed in the temperate hills. Present communication provides notes on taxonomy, distribution, habitat ecology and conservation of Neottia listeroides Lindl., an interesting leafless orchid in the state