Synthesis and characterization of novel liquid crystalline polymers containing cholesteryl pendant groups

In order to investigate the chiral effect of cholesteryl pendant groups on the induction of the cholesteric phase, a new cholesteryl-containing liquid crystalline monomer was synthesized and copolymerized with an achiral comonomer in various molar ratios. The layer-like arrangement of the smectic mesophase with different monomeric compositions of copolymers was investigated using an X-ray diffraction analysis. The cholesteric liquid phase was induced by the chiral segments; the dependence of the reciprocal central reflection wavelength on the mole fraction of the chiral monomer for copolymers was investigated. This paper demonstrates the effect of chiral pendant groups on the induction of the cholesteric phase and layered molecular arrangement of side-chain liquid crystalline polymers.     

羧酸吡啶类氢键液晶分子的合成及表征

以4-己氧基苯甲酸为质子给体,4-硝基苯乙烯基吡啶为受体,四氢呋喃为溶剂,制备了一种液晶超分子复合物—羧酸吡啶类氢键自主装型液晶复合物,用DSC和热台偏光显微镜对所合成化合物进行了相态和液晶性研究,并用IR1、H-NMR对所合成化合物进行了结构表征。结果表明:合成了目标化合物;IR结果证明了羧基和吡啶环间分子间氢键代替了羧基间的分子间氢键;相态及液晶行为研究证明了氢键复合物具有典型的热致液晶性能且呈现明显的向列型液晶态。     

Carbon nanotube dispersion in nematic liquid crystals: An overview

The aim of present review article is to present a comprehensive and current overview of scientific advancement in liquid crystal and carbon nanotube suspension. Particular attention has been paid to the recent developments and fundamental understanding of carbon nanotube dispersion in nematic liquid crystals. The dispersion and interaction of carbon nanotube in liquid crystal matrices and more elaborately the effect of dispersion on the properties of liquid crystalline materials has been extensively discussed. Recent progress has shown that even a very minute concentration of carbon nanotube in liquid crystals can have a reflective impact on the electrical and optical properties of liquid crystals. Liquid crystals provide a distinctive environment for controlling the alignment of carbon nanotubes whereas carbon nanotubes are important for the enhancement and fine-tuning of liquid crystalline properties. Potential applications of liquid crystal and carbon nanotube suspension are briefly discussed. Conclusion and future perspectives of this rapidly emerging field is provided at the end.     

新型液晶共聚酯的合成与表征

设计合成了对苯二甲酸 (4 ,4’ 二甲氧酰基 )二苯酯和间苯二甲酸 (4 ,4’ 二甲氧酰基 )二苯酯 ,并利用红外分析、核磁分析对液晶基元进行了表征。考察了温度和催化剂对液晶基元合成反应的影响。通过熔融酯交换法 ,以液晶基元为聚丁二酸丁二醇酯 (PBS)的共聚组分 ,合成了两个系列的液晶共聚酯。考察了催化剂种类及液晶含量对聚合物分子量的影响 ,并对其进行了表征     

Nano-engineering of the anchoring of liquid crystals on solid surfaces

The solid surface in the conventional liquid crystal displays, being responsible for the liquid crystal alignment in the absence of external fields, is playing only a passive role in the switching of the liquid crystal layer. Recently, we have shown that the anchoring strength and the easy axis, two important parameters characterizing the liquid crystal alignment, can effectively be controlled by light via photo-induced nano-scale changes of the solid surface properties. We have also introduced two novel concepts of commanded anchoring, the electrically commanded surfaces (for mediating switching of the liquid crystal) and the high performance alignment layers (for facilitating the switching of the liquid crystal) realized practically by means of a proper nano-engineering of the alignment layer. Electrically commanded anchoring concepts are strong candidates for implementation in a new generation of advanced liquid crystal displays and devices.     

共聚低热膨胀聚酰亚胺薄膜的制备与表征

以4,4′-(六氟异丙烯)二酞酸酐(6FDA)为含氟二酐,4,4′-二氨基-2,2′-双三氟甲基联苯(TFMB)为含氟二胺,通过引入分子结构相对对称的刚性单体1,2,4,5-均苯四甲酸二酐(PMDA)进行共聚合成了5种含氟比例不同的透明聚酰亚胺薄膜,并对其性能进行了表征。分析表明:引入刚性单体共聚后薄膜的热稳定性和耐热性有所提高;薄膜的介电常数随着PMDA含量的上升而增加;共聚薄膜在可见光领域的透光率低于均聚薄膜;拉伸实验显示在添加少量PMDA后,薄膜的拉伸强度和弹性模量有所增大,但当PMDA含量过高时其力学性能反而下降;随着PMDA含量的增加,薄膜的热膨胀系数明显降低。     

含柔性间隔基丙烯酸液晶化合物的合成及介晶性研究

以丙烯酸、溴乙醇、对羟基苯甲酸、4-羟基苯甲醛、4-甲氧基苯胺为原料,经醚化、酰氯化、酯化和希夫碱反应合成中间体和液晶化合物.通过红外光谱、核磁共振等对化合物的结构进行表征.最后利用偏光显微镜测试目标产物的液晶性能.结果表明:含柔性间隔基的化合物具有很好的向列相液晶性能,目标化合物的液晶相宽度达到110～C左右,具有广阔的应用前景.     

Optical properties of organo-soluble polyimide thin films and their applications in liquid crystal displays

Three organo-soluble polyimide powders have been synthesized. Their imidization was verified by Fourier transform infrared (FTIR) and thermal gravimetric analysis (TGA) techniques. The amorphous morphology of their thin films were confirmed by X-ray diffraction. Polyimide thin films were prepared by solution casting or spin coating. UV–visible transmission spectra of thin films revealed that they are almost transparent in the range of visible light. With in-plane orientation, revealed by FTIR spectra, negative birefringence (Δn) of thin films were observed, and refractive indices of the thin films along the film plane (n_TE) and normal to the plane (n_TM) were measured by a prism coupler. Because of negative birefringence of the thin films, they can be substituted for the compensation films for twisted nematic liquid crystal displays (TN-LCDs) to extend their viewing angles. In this paper, a 90°C TN-LCD and 120°C TN-LCD were taken as examples to show the compensation effect of thin films of a qualified polyimide.     

Na~+对KDP晶体热膨胀及硬度的影响

Na+是KDP原料中一种常见的杂质离子,采用"点籽晶"快速生长法生长了一系列掺杂Na+的KDP晶体,研究了不同掺杂浓度下Na+对KDP晶体热膨胀及硬度的影响。实验表明,随着Na+掺杂浓度的增大,KDP晶体Z向热膨胀系数逐步增大;KDP晶体(001)面的显微硬度整体大于(100)面的硬度,随着Na+掺杂浓度升高,KDP晶体各晶面硬度显著降低。     

Synthesis and characterization of tetraethylammonium tetrachlorocobaltate crystals

Single crystals of tetraethylammonium tetrachlorocobaltate were grown by solution method and characterized through single crystal X-ray diffraction, thermogravimetric analysis (TGA), differential scanning calorimetric studies (DSC) and infrared spectroscopic technique (IR). The crystals were bright, transparent and blue coloured. The unit cell parameters were found to bea =b = 90363 Å andc = 14.9879 Å and α = β = γ = 90°, showing tetragonal lattice from the XRD data. Thermogravimetric analysis showed a loss of weight at 683 K from which the decomposition reaction was formulated. Thermal anomalies were found for this crystal at temperatures 200 K, 220 K in the cooling cycle and at temperatures 200 K, 240 K in the heating cycle, respectively which showed that this crystal was associated with first order phase transition. All the vibrational frequencies corresponding to (TEA)⁺ ions and CoCl ₄ ^2? ions were assigned from the IR spectral data of this crystal.     

Pattern of liquid crystalline droplets induced by two beam interference in azobenzene derivative

A pattern of liquid crystalline droplets dispersed in the isotropic liquid can be formed during illumination by two interfering laser beams in certain range of the temperature and the light intensity. Azobenzene derivative substituted by long alkyl and alkoxy chains exhibiting smectic phases has been used for the study. The pattern can be reversibly erased and rewritten by shutting down and opening of the interfering beams. Polarized microscope images have shown the formation of numerous liquid crystalline droplets at bright regions of the interference fringes. Influence of the temperature and the light intensity has been studied by measuring the diffraction efficiency dynamics. Photothermal and photoorientational mechanisms of the formation of liquid crystalline droplets pattern have been proposed and discussed.     

共聚制备低热膨胀透明聚酰亚胺薄膜

为了在尽量不影响其透光性的前提下解决含氟聚酰亚胺薄膜热膨胀系数(CTE)过大的问题,以4,4′-(六氟异丙烯)二酞酸酐(6FDA)、4,4′-二氨基-2,2′-双三氟甲基联苯(TFMB)和3,3′,4,4′-联苯四羧酸二酐(BPDA)为原料,通过两步法合成了5种BPDA掺杂量分别为0、10%、20%、30%和40%的共聚PI薄膜,并采用红外光谱分析(IR)、热重分析(TGA)、热机械性能分析(TMA)等方法对其性能进行了表征.分析表明:共聚薄膜的热性能相比均聚薄膜有所提高;薄膜的介电常数与BPDA的含量成正比,而其在可见光领域的透光率与BPDA的含量成反比;在BPDA含量较低时,薄膜的拉伸强度和弹性模量随BPDA含量的增加而增大,但当BPDA摩尔分数超过30%时其力学性能开始降低;随着共聚单体含量的上升,薄膜的热膨胀系数大幅减小.     

含侧甲基液晶双马来酰亚胺的合成及表征

通过甲基对苯二酚和对马来酰亚胺基苯甲酸,制得了一种低熔点的酯类液晶双马来酰亚胺.应用FT-IR、1H-NMR、DSC、HSPM对液晶双马来酰亚胺的结构和液晶行为进行了表征.结果表明,这类液晶双马来酰亚胺具有较低的熔点,侧甲基的存在使得液晶双马来酰亚胺的熔点下降了39℃.由HSPM观察到所合成的液晶单体具有向列型液晶所具有的典型的纹影织构,呈现出较好的热致液晶行为,并且液晶织构可以通过端基的交联聚合反应固定在交联网络中.     

Effect of stoichiometry on the thermal expansion coefficients of lithium niobate single crystals

The chemical analysis of LiNbO₃ single crystals, with different melt compositions (Li/Nb) _m =0·945, 1·0, 1·1 and 1·2, grown by slow cooling technique, reveals a remarkable difference in solid and melt compositions. The thermal expansion coefficients alonga andc axes, determined by using Newton’s ring experiment, are found to increase anisotropically with increase in (Li/Nb) _m ratio. The variation in thermal expansion coefficient with increase in the (Li/Nb) _m ratio is discussed in the light of defect chemistry i.e. the partial replacement of Li⁺ by excess Nb⁵⁺ creates additional cation vacancies to attain the electro-neutrality in the crystal.     

Quadrupolar moment calculations and mesomorphic character of model dimeric liquid crystals

Model dimeric compounds CH₃---(CH₂)_nCOO---R---OOC---(CH₂)_p---COO---R---OOC(CH₂)_n---CH₃, where (R=---C₆H₄---C(CH₃)=HC---C₆H₄---), of semiflexible liquid crystal polymers (LCP) have been studied by molecular modeling techniques. First, a conformational analysis of the molecules was made in order to find the lowest energy conformation structure. In a second stage, geometry optimization calculations of these conformers were performed at the quantum mechanics semiempirical PM3 level. Some molecular parameters (electric dipolar and quadrupolar moments) were obtained at the improved ab initio Hartree–Fock HF/6-31G(d)//PM3 level and are related with the mesomorphic character of these systems. It is found that the trace of the quadrupole moment tensor correlates with the spacer (---(CH₂)_p-linkage) length, and this can be an indication of the trend that this magnitude exhibits in aromatic liquid crystal systems.     

Langmuir-Blodgett films of palladium(II)-imidazole liquid crystals

The self-assembly of organic-inorganic compounds of palladium(II)-bis(N-long chain substituted imidazole) dichloride complexes has been investigated. The presence of a hydroxyl group at the 2-position of alkyl chain induced liquid crystal properties. Molecular ordering of Pd(II)-imidazole complexes upon mechanical compression at the air/water interface is studied by surface pressure-area (π-A) isotherms and Brewster angle microscope. Incorporation of lateral hydroxyl group in the alkyl chain enhances the stability of the films via intramolecular hydrogen bonding interactions. Langmuir-Blodgett (LB) films formed by these compounds were studied by various techniques to characterize their surface morphology, hydrophilic/hydrophobic property, surface functionalities and interlayer spacings. U-shaped interdigitated assembling, good crystallinity and in-air stability of these LB films were demonstrated.     

Photorefractivity in polymer dissolved liquid crystal composites composed of low-molecular-weight nematic liquid crystals and copolymer comprising mesogenic side groups

This paper describes the photorefractive effect of the liquid crystalline composite materials comprising low-molecular-weight nematic liquid crystals (L-LC), copolymer with mesogenic side groups and a small amount of photosensitizer. Copolymers with four kinds of mesogenic side groups were investigated with respect to the compatibility between the L-LC and the copolymer and the photorefractivity of the composites. Two of them could be miscible with L-LC and the composite exhibited LC phase even though the copolymer itself did not show a LC phase. High gain coefficients (> cm^K1) under the low applied dc electric field (<1V/mm) was observed when the composites showed a mesophase without any macroscopic phase separation.     

Synthesis and structural characterization of Tm:Lu2O3 nanocrystals. An approach towards new laser ceramics

Nanocrystals of Tm³⁺ Thulium doped cubic sesquioxides, Tm:Lu₂O₃, with a maximum size around 30 nm have been synthesized by a modified Pechini sol-gel method. The calcination temperature for the synthesis is 1073 K. Electron microscopy was used to analyze the presence of aggregates, and the type of boundary between the nanocrystals. The linear coefficient of thermal expansion for these nanocrystals has been determined to be around 7.5 × 10⁻⁶ K⁻¹. The growth of the nanocrystals has been studied in terms of temperature and time. Nanocrystals start to grow at temperatures around 1267 K. Finally, the grain growth activation energy of this material has been evaluated to be 76 kJ/mol, indicating a diffusion growth mechanism. Linear thermal expansion of prepared nanocrystals is ≈7.5 × 10⁻⁶ K⁻¹.     

Langmuir Blodgett films of arachidic acid and a nematic liquid crystal: Characterization and use in homeotropic alignment

We study the behavior of a mixed Langmuir monolayer consisting of a fatty acid and a nematic liquid crystal. We demonstrate that the mixed monolayer successfully transfers as a Langmuir-Blodgett film and characterize the transferred film using UV spectroscopy. An important application of Langmuir-Blodgett films is in the alignment of liquid crystals for electro-optical applications, such as displays. We show that including the liquid crystal in the Langmuir-Blodgett film produces homeotropic alignment for a system which fails to align by other standard techniques.     

四-(对酰氧基苯基)卟啉的合成及液晶性能研究

合成了4个系列的中位－四（对酰氧基苯基）卟啉化合物，通过元素分析，紫外－可见光谱，红外光声光谱和核磁共振氢谱等分析手段表征了4种卟啉自由碱化合物，并肜DSC和偏光显微镜研究这些化合物的液晶行为，探讨了碳链长度对卟啉自由碱液晶性能的影响。