Novel achiral four-ring bent-shaped nematic liquid crystals with trifluoromethyl and methyl substituents in the central molecular core: an unusually large Kerr constant in blue phase III of nematic-chiral dopant mixture
Nematic phases in achiral unsymmetrical four-ring bent-core azo compounds possessing strongly polar cyano and nitro moieties as end substituents: Synthesis and characterization
transverse direction of the molecule. The molecular structure characterization is consistent with elemental and spectroscopic analysis data. The materials thermal behaviour and phasecharacterization have been investigated by differential scanning calorimetry and polarizing optical microscopy. All the compounds exhibit enantiotropic nematic phase over a widetemperaturerange. The light induced cis–trans
Orthogonal smectic and nematic ordering in three-ring polar bent-core molecules with anti-parallel arrangement
作者:Supreet Kaur、Vidhika Punjani、Golam Mohiuddin、Santanu Kumar Pal
DOI:10.1039/c7nj00272f
日期:——
are shown to exhibit nematic and orthogonal smectic phases at lower temperatures. The occurrence of the orthogonal smectic and nematicordering has been confirmed by optical texture, DSC study and temperature dependent X-ray diffraction measurements. X-ray structure analysis in the crystalline state of one of the compounds (2-4) ascertained the antiparallel arrangement of the polar bent-core molecules
Viscoelasticity, dielectric anisotropy, and birefringence in the nematic phase of three four-ring bent-core liquid crystals with an L-shaped molecular frame
作者:Nejmettin Avci、Volodymyr Borshch、Dipika Debnath Sarkar、Rahul Deb、Gude Venkatesh、Taras Turiv、Sergij V. Shiyanovskii、Nandiraju V. S. Rao、Oleg D. Lavrentovich
DOI:10.1039/c2sm26448j
日期:——
Molecular shape is an important factor in determining the material properties of thermotropic liquid crystals (LCs). We synthesized and investigated several LC compounds formed by asymmetrically bent molecules with a rigid four-ring core in the shape of the letter ‘L’. We measured the temperature dependencies of dielectric permittivities, birefringence, splay K1 and bend K3 elastic constants, splay viscosity ηsplay and flow viscosities η|| and η⊥. The bend–splay anisotropy δK31 = K3 − K1 is negative, similar to the case of nematic LCs formed by symmetrically bent molecules of V-shape. The dielectric anisotropy Δε and birefringence are positive in the entire nematic range. The splay viscosity ηsplay and the flow viscosities η|| and η⊥ are smaller than the viscosities measured for the symmetric V-shaped bent-core materials at similar temperatures. The ratio Γ = ηsplay/η||,⊥ is in the range 5–4 that is typical for rod-like LCs. The reported L-shaped bent-core nematic LCs combine the useful features of bent-core LCs (such as a negative δK31, suitable for formulation of broad-range blue phases) with the relatively low viscosities, a property typical for rod-like LCs and beneficial for electro-optic switching applications.
分子形状是决定热致液晶(LC)材料性质的重要因素。我们合成并研究了几种由不对称弯曲分子构成的液晶化合物,这些分子具有一个形状像字母“L”的刚性四环核心。我们测量了介电常数、双折射、撓曲 K1 和弯曲 K3 弹性常数、撕裂粘度 ηsplay 以及流动粘度 η|| 和 η⊥ 的温度依赖性。弯曲-撕裂各向异性 δK31 = K3 − K1 为负,类似于由对称弯曲的 V 形分子形成的向列型液晶的情况。介电各向异性 Δε 和双折射在整个向列相范围内均为正。撕裂粘度 ηsplay 和流动粘度 η|| 及 η⊥ 小于在类似温度下测得的对称 V 形弯曲核心材料的粘度。比率 Γ = ηsplay/η||,⊥ 在 5-4 范围内,这是典型的杆状液晶的特征。报道的 L 形弯曲核心向列型液晶结合了弯曲核心液晶的有用特征(例如负的 δK31,适合于广范围蓝相的形成)与相对较低的粘度,这是杆状液晶的典型特性,对于电光开关应用具有益处。