Advances in Liquid Crystals

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Authors: Zi Qiang Huang
Abstract: Active matrices often related with high grade display devices, due to application of the storage elements, typically thin film transistor (TFT). Because of the complex procedures in the manufacturing TFT, investment of the high value manufacturing equipments and clarification plants is necessary, hence increasing the manufacturing cost of the flat panel, and more importantly, causing the pollution of water and air. As the contribution of TFT array merely exists in supplying storage function for the pixels of the display panel, large efforts have been made to find suitable cells that have bistable effect, so as to substitute the effect of TFT. As the bistable cell is just the storage pixel, one could construct a bistable cell to skip the needs of TFT active matrices. The paper is to introduce currently available bistable display devices in the following field: liquid crystal bistable displays with cholesteric liquid crystals, which is an example to introduce the bistable technology; iMod display devices based on mechanic induced bistable and light interference, which shows the possibility to construct bistable display; and the display based on solid powder movement in air or in vacuum, so called liquid powder displays, which shows how to improve the existed display.
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Authors: Yuan Ming Huang, Bao Gai Zhai
Abstract: With the ultraviolet-visible spectrometer and photospectrometer, we have investigated the optical absorption and light emission from the dilute tetrahydrofuran solutions of a classical banana-shaped liquid crystal 1,3-phenylene-bis[4-(4'-nonyloxy)phenyliminomethyl]benzoate. In the dilute tetrahydrofuran solutions, three optical absorption bands were recorded for the banana-shaped compound at about 255, 290 and 355 nm, respectively. Upon the 325 nm excitation, white light emissions were recorded for the solid phase of the banana-shaped liquid crystal whereas blue-greenish emissions were observed for the banana-shaped molecules in dilute solution.
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Authors: Shu Fang Fu, Jing Bai, Sheng Zhou, Xiu Rong Qu, Hua Li, Xuan Zhang Wang
Abstract: The effect of molecular shape on molecular configuration of liquid crystalline polymers under shear flows is numerically analyzed using the extended Doi theory. We can find that the molecular shape strongly affects on the transition among flow-orientation modes. The change in sign of the first normal stress difference is to speed up by the increasing .
216
Authors: Yuan Ming Huang, Bao Gai Zhai
Abstract: The effects of ionic conductivity on the electro-optical properties of a chiral banana-shaped liquid crystal 1,3-phenylene bis{4-[3-chloro-4-(3,7-dimethyloctyloxyl)] phenyliminomethyl} benzoate were investigated with the techniques of polarizing optical microscopy and dielectric spectroscopy. When the banana-shaped liquid crystal was experienced a low-frequency (1 Hz) triangular waveform electric field, its polarizing optical microscopic textures were first turned into gray and then into black at about 95oC, a few degrees lower than the clearing temperature of the banana-shaped liquid crystal. Detailed dielectric spectroscopic characterizations showed that ionic conductivity increased exponentially as the temperature increased from 72 to 110oC. Our results suggested that dominant ionic conductivity near its clearing temperature is responsible for the electric-field induced loss in the birefringence of the banana-shaped liquid crystal.
220
Authors: I Min Jiang, Yu Jen Chen, Wen Chi Hung, C.T. Kuo, D.J. Jang, Chia Chi Shih, Ming Shan Tsai
Abstract: Nematic liquid crystals (NLCs) can be easily reoriented by the laser beam at the temperature closed to the nematic–isotropic phase transition (TNI). At the temperature closed to TNI, the propagating mode of laser beam and the optically induced phase transition were explored by using a microscopic conoscope technique. This investigation demonstrates the formation of soliton at particular beam propagation modes. The interaction between nematic liquid crystals and the laser beam with different polarizations showed the nonlinearity in optical alignment.
224
Authors: Qing Lan Ma, Yuan Ming Huang
Abstract: Periodically birefringent thin films growing out of the isotropic phase of the banana-shaped liquid crystal 1,3-phenylene-bis (4-butoxybenzyldiamine) were investigated with polarized optical microscopy. The gown thin films of the periodic modulation of the birefringent index self-assembled by the banana-shaped LC molecules were attributed to the difference of the molecular composing structures. Further the driving forces of the banana-shaped molecular self-assembly were discussed.
228
Authors: Cai Juan Xia, Han Cheng Liu, Peng Fei Cheng, Chang Feng Fang
Abstract: Using nonequilibrium Green’s function and first-principles calculations, we investigate the effects of different molecular conformations induced by torsion angle on electronic transport and their stability in 4,4′-biphenyl bis (dithiocarboxylate) molecular junction under an applied electric field. The results indicate that there are two stable conformations existed in this molecular junction as external bias increasing. An electric field can be used to “switch” one conformation to the other, and there is an abrupt change in the degree of torsion angle in this process. This change is expected to cause a conductance switching in the system. Furthermore, the transport mechanism of this conformational molecular switch is discussed in detail.
232
Authors: Wei Wei Liu, Yuan Ming Huang
Abstract: Lyotropic liquid crystal synthesized by sodium dodecyl sulfonate in the mixed solvent of distilled water through make the different concentration. Using Polarized optical microscopy and ultraviolet-visible spectrometer and theoretical simulation, we have studied the relation between the samples concentration and light scattering. Our results have demonstrated that natural light scattering increased with the samples concentration increased. The results we have gotten now are almost equal to our theoretical simulation.
237
Authors: Jia Ling Wang, Xin Du, Jia Lv, Tian Chi Yu, Zhi Xin Fan
Abstract: For the cholesteric liquid crystal (hereinafter short for Ch-LC) possesses special optical properties, it has specific applications in the area of liquid crystal displays and optoelectronic devices. Specimens of Ch-LCs in planar and focal conic texture stably are prepared. The photographs of textures are shot by polarizing microscope and transmittance spectrums of different textures are measured by spectrophotometer. It is found that the specimen in focal conic texture with large crystal domains has the well transmission property. The experiment has an important significance for applications of liquid crystals.
241
Authors: Yuan Ming Huang, Qing Lan Ma, Bao Gai Zhai
Abstract: The influence of cooling rate on the phase transitions of a three-benzene-ring containing bent-core liquid crystal 1,3-phenylene-bis[4-(hexylcarboyloxyl)benzylideneamine] has been investigated by means of differential scanning calorimetry and polarized optical microscopy. Our results show that the cooling rates in the second cooling run pose significant effects on the phase transitions of the bent-core liquid crystal despite the cooling rates in the first cooling run pose little effects on the phase transitions. In the second cooling run, the banana phases survived only when the cooling rates were in the range of 14~15oC/min whereas both slow cooling rates which were less than 13oC/min and fast cooling rates which were higher than 16oC/min made the banana phases disappeared.
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