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271.
2H NMR spectroscopy is employed to investigate the orientational order, molecular structure and phase transitions of the chiral smectic liquid crystal 1-methylheptyl 4'-(4-n-decyloxybenzoyloxy)biphenyl-4-carboxylate (10B1M7), showing smectic A, C* and J phases, as well as several sub-smectic C* phases. Two optically pure, differently deuteriated isotopomers have been purposely synthesized and studied. 相似文献
272.
G. Gesekus I. Dierking Corresponding author S. Gerber M. Wulf V. Vill 《Liquid crystals》2013,40(2):145-152
This paper describes the synthesis and physical properties of a chiral bent-core liquid crystal containing the chiral non-aromatic central ring system 1,5-anhydro-2-desoxy-D-arabino-hexitol. The preparation involved a stepwise construction of the mesogenic side chains via a selective diesterification of glucal at positions three and six with 4-O-acetylbenzoyl chloride followed by selective deacetylation. Repeated esterification of the aromatic hydroxy group with a substituted benzoic acid and hydrogenation of the double bond resulted in the desired product. To our knowledge, this is the first banana shaped liquid crystal synthesized containing a sugar derivative as a chiral core. Investigation of the mesogenic properties and electro-optic experiments showed traditional calamitic phases along with banana phases. 相似文献
273.
In this work a set of experimental data points is used to study some scaling properties of Miesowicz coefficients. Using the fact that all the compounds studied present two critical points—the crystal–nematic and the nematic–isotropic phase transitions—a common temperature scale was defined. With the use of this unique temperature scale two relevant aspects that distinguish the viscosity of these materials can be simultaneously extracted and studied: (1) the molecular shape anisotropy and (2) the different strengths of molecular interaction of the different compounds. Through the study of the scaling properties associated with these properties, the existence of a common law connecting the Miesowicz coefficients with the associated decay time is proposed. 相似文献
274.
Cuihong Zhang Dongrui Wang Hui Cao Ping Song Chaoyong Yang Huai Yang Guo‐Hua Hu 《先进技术聚合物》2013,24(5):453-459
In this paper, polymer dispersed liquid crystals (PDLC) films with LC content as low as 40 wt% were prepared, and the electro‐optical properties were carefully investigated. To accomplish this, different (meth)acrylate copolymerizaiton monomers have been used. The electro‐optical properties and morphologies of the PDLC films were strongly influenced by the chemical structure of copolymerization monomers (hydroxypropyl methacrylate (HPMA), glycidyl methacrylate, hydroxypropyl acrylate) and their feed ratio. Lower driven voltage and higher contrast ratio were achieved when the PDLC films showed a morphology with suitably LC domain size. At high HPMA content, a thin polymer film was formed on the surface of PDLC samples, which is beneficial to decrease the total LC content in PDLC devices. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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276.
《Particuology》2018
Particle coatings are used extensively to generate dispersed solids with well-defined properties, e.g., to protect active ingredients, with most coating processes using core particles of a diameter larger than 200 μm. This work contributes to the development of a coating process for fine dispersed particles (diameter less than 50 μm) by combining two particle-formulation processes, namely, coating and spray drying. The feasibility of the operation is based on and demonstrated by the innovative application of a two-fluid nozzle. Experiments were conducted by using glass particles as core particles and sodium benzoate as the coating agent. The coating of finely dispersed particles is achieved by the spraying of particles and coating solution as a homogeneous suspension. The aim is to create droplets with only one contained particle at the nozzle outlet. After evaporation of the water in the droplet, a thin solid film is built on the particle surface. The suspension viscosity was measured and compared with empirical equations from the literature. The liquid-film thickness on the particle surface was calculated to predict the building of a uniform coating layer or agglomerates. In this study, the feasibility of pneumatic transport through the nozzle and an investigation of the process were illustrated. The agglomeration fraction and degree of coating of the particle surface were analyzed optically by scanning electron microscopy. In this way, the influence of different processes and suspension parameters on the product quality were determined. 相似文献
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279.
以高比表面积的介孔二氧化硅为载体, 采用等体积浸渍法制备了一系列介孔二氧化硅负载钒催化剂, 并探究了其乙烷选择氧化反应性能. 利用X射线衍射(XRD)、 紫外-可见漫反射光谱(UV-Vis DRS)和氢气程序升温还原(H2-TPR)等方法对催化剂的物化性质进行了表征, 研究了钒负载量对催化剂结构特征的影响. 结果表明,随着钒负载量的增加, 钒物种在催化剂表面的存在形式由高分散低聚的VO x 转变为高聚的VO x, 其中高分散钒物种有利于提高目标产物乙烯和乙醛的选择性. 相似文献
280.
We developed a highly regioselective synthesis of multi-substituted alkenylboronates via a heterogeneous ligand-free nano-copper catalyst that was highly dispersed and supported on the porous polyvinyl chloride. In this catalytic system, substituents on the terminal alkynes could affect the configuration of products. Terminal alkynes and general internal alkynes gave β-selective borylation products, whereas heteroatom-substituted alkynes like alkynamides, thioacetylenes, and ynol ethers gave α-selective borylation products in good chemical yields with exclusive regioselectivity. 相似文献