Advances in Liquid Crystals

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Authors: Xin De Tang, Nian Feng Han, Jing Xu
Abstract: A2BA2-type amphiphilic liquid crystalline block copolymers containing azobenzene were synthesized by atom transfer radical polymerization (ATRP). The macroinitiator prepared by the esterification reaction between poly(ethylene glycol) (PEG) and 2,2-dichloroacetyl chloride was used to initiate the ATRP of 6-[4-(4-ethoxyphenylazo)phenoxy]hexyl methacrylate (M6C). The resulting macroinitiator and block copolymers were characterized by 1H NMR, gel permeation chromatography (GPC). Polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) preliminarily revealed the liquid crystalline property of these block copolymers. These novel amphiphilic liquid crystalline block copolymers are promising in some areas, such as optical data storage, optical switch, and molecular devices.
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Authors: Jian Feng Ban, Shao Rong Lu, Chen Xi Zhang
Abstract: A series of novel biphenylnate liquid crystalline polyurethanes (BLCPs) were synthesized by polyaddition reaction of 4,4’-dihydroxybiphenyl with 2,4-TDI(2,4-toluenediisocyanate) and diethylene glycol through changing the molar ratio of diphenol and diol. The thermotropic properties, the melting point (Tm) and the isotropization temperature (Ti) of the synthesized polyurethanes were characterized by FT-IR, DSC, POM and WXRD. The results of experiments showed that all of the polyurethane polymers exhibited thermotropic liquid crystalline properties between 130°C and 230°C. The transition temperature (Tm and Ti) decreased with an increase in the length of the flexible chain.
158
Authors: Qing Yan, Ping Hu, Wen Hao Yu, Bi Qin Wang, Ke Qing Zhao
Abstract: To investigate the influence of alkyl chain on thermotropic and mesomorphic properties of 1,1’-disubstitued ferrocene derivatives, two series of ferrocene derivatives containing Schiff's base, 1,1’-C8H17FcC6H4COOC6H4CH=NC6H4OOCC6H4R1 (R1 = H, OCnH2n+1, n = 2, 4, 6, 8 ) and 1,1’-C8H17FcC6H4COOC6H4CH=NC6H4N=NC6H4R2 (R2 = Br, Cl, CH3 ) have been synthesized and characterized by IR and 1H NMR. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) results showed that all compounds exhibit nematic mesophase. The results show that the flexible alkyl chain connecting with ferrocene moiety could lower the melting points and clearing points, favor the formation of nematic mesophase.
162
Authors: Yuan Ming Huang
Abstract: A three-ring containing bent-core compound 1,3-phenylene-bis(4-butoxybenzylidene amine) was synthesized and characterized with differential scanning calorimetry and polarized optical microscopy. It exhibited mesophases in the temperature range of 48-54oC for the first cyclic heating and cooling. Our results demonstrated that three-ring containing bent-core molecules can form mesophases.
167
Authors: Muklesur Rahman, Wei Lee
Abstract: Colloids composed of liquid-crystal hydrosols exhibit a rich set of interesting phenomena. The coupling between liquid-crystalline media and colloidal particles plays an essential role leading to an abundant source of new physics. In the last few years, peculiar behaviors of carbon-nanotube-doped calamitic liquid crystals have attracted considerable attention. This paper provides a brief introduction to this alluring subject for its on-going research development in this laboratory. First presented are our current understandings of the nematic colloidal system comprising carbon nanotubes and of their possible orientation and dynamics under the application of an external field. Various electro-optical and electrical properties of a liquid-crystal display rectified by the nanoscale carbonaceous guest are then addressed to a larger extent. Dielectric relaxation obtained from a nematic impregnated with carbon nanotubes is also discussed. With historical significance for the dawn of the liquid-crystal–carbon-nanotube research, several important findings of enhanced nonlinear optical properties in typical nematic mesomaterials consisting of suspended nanotubes are delineated. With the new colloidal systems of elongated nanoscale solids dispersed in anisotropic fluids in the mesophase, many new intriguing phenomena are awaiting theoretical and experimental explorations. Collaborations are called to draw attention of interested theoretical physicists, in particular.
173
Authors: Yuan Ming Huang, Bao Gai Zhai
Abstract: The optical absorption and photoluminescence spectra of banana-shaped molecules 1,3-phenylene bis(4-methoxybenzylideneamine) have been investigated with an ultraviolet-visible spectrometers and a spectrofluorometer, respectively. The optical characterizations indicate that the banana-shaped molecules exhibit strong absorptions in a broad range of 260-370 nm and that they can give off strong purple photoluminescence when excited by ultraviolet photons. Using Hückel tight-binding program, we have calculated the electronic structures of the banana-shaped molecules. In light of the calculated electronic structures, the origin of the purple photoluminescence is discussed, and our results have demonstrated that not only the lowest unoccupied molecular orbital and the highest occupied molecular orbital but also the localized energy levels of the lone pairs are responsible for the recorded purple photoluminescence.
182
Authors: Wen Jun Zheng, Chen Yan Chiang, Chi Wi Ong
Abstract: The effect of temperature on the tilt of discotic columns in a columnar phase has been studied. The homogenous alignment of discotic columns is achieved by applying a mechanical shearing. In the columnar phase, the tilt of the discotic columns at substrate surface is found to change with temperature. A decrease in the temperature of the substrates causes an increase in the pretilt of the discotic columns. The phenomenon is explained based on the consideration of surface free energy at the interface of the substrate.
186
Authors: Lan Li Chen, Bao Gai Zhai, Yuan Ming Huang
Abstract: We have investigated the photostability of an antiferroelectric banana-shaped liquid crystal 4-chloro-1,3-phenylene bis [4-(4-n-tetradecyl) phenylimino methyl] benzoate by measuring its polarization as a function of photo-irradiation duration. Upon intense photo-irradiation for three hours, the banana-shaped liquid crystal exhibits a significant photostability although it bears the linkages of –COO– and –CH=N–.
194
Authors: Jing Bai, Shu Fang Fu, Xuan Zhang Wang
Abstract: Nonlinear bulk polaritons in uniaxial antiferromagnetic film are investigated under a magnetic field that is along the anisotropy axial. The numerical calculations show that the nonlinear shift in frequency is very obvious. The antiferromagnetic film presents the strong anisotropy under the magnetic field.
198
Authors: Bao Gai Zhai, Lan Li Chen, Yuan Ming Huang
Abstract: By triangular wave method, the polarization currents of an azo-containing banana-shaped antiferroelectric liquid crystal were investigated as a function of the time of 365-nm ultraviolet irradiation. Under the 365-nm irradiation, the polarization currents were observed to evolve with the time of ultraviolet irradiation until they diminished. The roles of photoisomerization, photolysis and thermolysis were discussed for the azo-containing banana-shaped liquid crystal.
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