Liquid Crystals and Related Materials II

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作者: Mohammed Ibn-Elhaj, Sabrina Chappellet, Frédéric Lincker
摘要: Rolic® Light Controlled Molecular Orientation (LCMO) technology is the basis for todays advanced mass production technologies for large LCD-TV panel, high-resolution 3D patterned-retarders and high-resolution optical security devices. This fundamental technology allows an easy achievement of high resolution azimuthal LC-director patterns with defined bias angles, from homogeneous planar to homeotropic orientation, depending on the target application [1-7]. In addition to the control of bias angles, LCD panel manufacturers require alignment layers with a wide range of optimized properties. Thin alignment films must be easily coatable and should have high photosensitivity in order to achieve fast processing. The photoalignment film should also have high stability and good electrical properties such as Voltage Holding Ratio (VHR), Residual DC (RDC) and image sticking. Because of in-situ photo crosslinking during processing [1, 2], our proprietary LCMO photoalignment technology is shown to be thermally and optically stable. Last years, enormous progress has been made in the development of advanced materials that meet all requirements for mass production of large-area flat panel displays. LCMO-VA technology, for vertical alignment LCDs, is the basis for the state of the art UV2 A production technology recently used in the manufacturing of advanced new generation LCD-TV panel displays with reduced production costs and low energy consumption [8, 9]. LCMO-VA mechanism and performances of state of the art materials will be discussed.
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作者: Geetha G. Nair, R. Bhargavi
摘要: In this article, results of static/dynamic Freedericksz transformation and rheological studies on anisotropic thermoreversible gels formed by gelation of a nematic liquid crystal (NLC) with a monodisperse dipeptide are presented. Freedericksz transformation studies reveal a surprising result: the gel state possesses a very large Frank bend elastic constant value, order of magnitude higher than the sol state, whereas, the splay elastic constant shows relatively a small increase. The studies also demonstrate that the anisotropic gel to anisotropic sol transition can be tracked by simply monitoring the Freedericksz transformation. Other attractive features of the gel state include the vanishing of the undesirable backflow effect, and nearly an order of magnitude decrease of switching speed. Further, rheological studies bring out the soft glassy characteristics of these gels.
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作者: Kazuki Hiro, Tadahiro Wada
摘要: Phase diagrams including absolute negative pressure regions of thermotropic liquid crystals give useful information on science and technology. A phase diagram was depicted for ca. 40mg of a thermotropic liquid crystal in a pressure vs. temperature (P-T) plane by the Berthelot method using a metal tube. N-I phase transitions occurred even under-10MPa, and a polymorphism of the crystalline phase was observed.
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作者: Benjamin I. Outram, Steve J. Elston
摘要: The difference between e1 and e3 parameters for flexoelectric polarization, as originally defined byMeyer, is measured for nematic liquid crystal materials E7 and BL087 in Twisted Nematic (TN) cells with In-Plane Switching (IPS) electric fields using the crystal rotation method, which measures transmission as a function of angle of incidence. Values of e1 − e3 for E7 and BL087 are found to be 7.2±1.0 pCm−1 and 9.4±1.0 pCm−1 respectively.
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作者: Qing Lan Ma, Rui Xiong, Yuan Ming Huang
摘要: A typical liquid crystal (LC) N,N-(terephthalylidene) bis (4-decylbenzenamine) (TB10A) was firstly synthesized at room temperature. The synthesized LC TB10A were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), ultraviolet-visible (UV-vis) spectrophotometry, photoluminecence (PL) spectroscopy and electronic structure calculations. Upon the 325 nm excitation, the dilute tetrahydrofuran solutions of TB10A could give off blue PL. With Hückel tight-binding method, the electronic structures of the TB10A were calculated. Our results demonstrated that the deep-blue PL observed at about 489 nm (2.54 eV) can be assigned to the π* → n transition for the TB10A.
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作者: Ming Tao Run, Qing Chang Zhang, Wen Zhou, Yu Zhong
摘要: The crystal morphology, melt-crystallization and mechanical properties of poly (trimethylene terephthalate)/maleinized poly (octene-ethylene)/organo-montmorillonite nanocomposites were investigated by using polarized optical microscopy (POM), differential scanning calorimetry (DSC) and universal material testing machine, respectively. The results suggest that the nanocomposites form smaller or imperfect microcrystallites with lower melting point due to the influence of OMMT components and the nanocomposites have increased crystallization rate because OMMT is an effective nucleation agent. However, the crystallinity decreases because of the thickening effect of OMMT in the composites. The nanocomposite with 2%OMMT has the largest tensile and impact strength.
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作者: D. Madhavi Latha, V.G.K.M. Pisipati, M. Ramakrishna Nanachara Rao, P.V. Datta Prasad
摘要: Ultrasonic velocity measurements are carried out on four nOm compounds viz., N-(p-n-methoxy and ethoxy benzylidene)-p-n-dodecyl and tetradecyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. The first three compounds exhibit mono variant nematic phase while the last compound exhibits nematic and smectic-A phases with variable thermal ranges. The temperature dependence of sound velocity, U shows minima at the isotropic-nematic and nematic-smectic-A transitions. In conjunction with the density data of these compounds, the thermo acoustic parameters such as adiabatic compressibility (βad), the molar sound velocity (Rao’s number) (Rn), molar compressibility (W), molecular free length (Lf) and available volume (Va) are estimated. In addition the intermolecular free length (Lf) is estimated in three different ways employing density and ultrasonic velocity data. The results are compared with the data available in literature of other compounds.
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作者: Xin De Tang, Ye Chen, Xin Wang, Fa Qi Yu, Mei Shan Pei
摘要: A novel liquid crystalline polymer bearing azobenzene groups in both main chain and side chain has been successfully synthesized by atom transfer radical polymerization (ATRP). Dual bromide-terminated azobenzene was used as the initiator for the ATRP of azobenzene-containing monomer (M6C). The structure of the resulting polymer was confirmed by nuclear magnetic resonance (NMR), and the molecular weight and its dispersity was characterized by gel permeation chromatography (GPC). The mesomorphic properties of this novel polymer were characterized by means of polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The results demonstrated that this polymer can form mesophases.
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作者: Shu Fang Fu, Qiang Zhang, Qiang Hua Li
摘要: The effect of magnetic fields on the molecular configuration of liquid crystalline polymers (LCPs) under simple shear flows is numerically simulated using the Doi theory when the initial state of the director is out-of-plane. A method of effectively enhance the order parameter is discussed in this paper. The simulation results show that the degree of molecular alignment can be greatly increased along the direction of the magnetic field. It is an efficient way to improve the performance of LCP materials.
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