Advances in Liquid Crystals

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Authors: Wen Hao Yu, Yue Feng Bai, Yang Jing, Shi Chang Nie, Bi Qin Wang, Ping Hu, Ke Qing Zhao
Abstract: A series of disk-rod-disk liquid crystal trimers have been synthesized. Two triphenylene discogens have been connected to a biphenyl mesogen via CuI-NEt3 catalyzed alkyne azide cycloaddition in toluene at room temperature. The trimers have been characterized by using 1H NMR, IR, high resolution Mass spectra and the mesomorphic properties investigated with polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction. The result shows that the trimers exhibited rectangular columnar mesophase (Colr). The length of the flexible spacer connecting the three segments has important influence on the thermal behaviors of the trimers.
Authors: Wen Jun Yang, Guo Zhu Liu, Ji Min Wang, Du Ling Xia
Abstract: Birefringence of a polymer is caused by polymer chain orientation during an injection-molding, extrusion processing or heat drawing. Birefringence of polymers degrades the performance of optical devices that require focusing by lenses or maintaining the polarization state of incident light. Optical polymers which exhibit no birefringence with any orientation of polymer chains are desirable to realize high performance optical devices that handle polarized light. In this study we demonstrate the random copolymerization method for synthesizing the zero-birefringence polymers in which positive and negative birefringence homopolymer are blended. We synthesize a polymer that exhibits no orientational birefringence with any orientation degree in a system that is composed of Methyl methacrylate/Styrene/Benzyl methacrylate.
Authors: Jian Qiang Liu, Xing Cheng Zhang, You Yong Dai, Hong Di Xiao, Shi Shen Yan, Wan Guo Hou
Abstract: A new organometallic palladium coordinated liquid crystal that is written by PdS4 has been synthesized by chelating reaction of the tetrachloropalladate (PdCl42-) and the star-like liquid crystal (S4) containing four butoxyazobenzene mesogens in its periphery. The structure and liquid crystallinity (LC) of PdS4 were characterized by infrared absorption spectroscopy (IR), ultraviolet absorption spectra (UV), nuclear magnetic resonance spectroscopy (NMR), elemental analysis (EA), polarizing optical microscope (POM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The phase behavior of PdS4 is Cr167N232I200N170Cr, its melting point and clearing temperature are higher than those of the free azo ligand S4, its mesophase range is broader than S4’s. It will be used as a new type photoelectric functional material in the future.
Authors: Xin De Tang, Long Cheng Gao, Nian Feng Han
Abstract: The influence of the terminal substituent of azobenzene on the liquid crystalline property of ABA triblock copolymers was studied. Three kinds of azobenzene-containing monomers with different terminal substituents were respectively used to synthesize ABA triblock copolymers (denoted as PMMAzo12-PEG13-PMMAzo12, PEMAzo14-PEG13-PEMAzo14, and PNMAzo14-PEG13-PNMAzo14) by atom transfer radical polymerization (ATRP). These copolymers were characterized with 1H NMR and GPC, and exhibited controlled molecular weights and narrow molecular weight distributions. Differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) have shown that these copolymers have mesophases. PMMAzo12-PEG13-PMMAzo12 has a smectic mesophase and a nematic mesophase, while both PEMAzo14-PEG13-PEMAzo14 and PNMAzo14-PEG13-PNMAzo14 have a nematic mesophase. This demonstrates that the LC properties of these copolymers highly depend on the terminal substituent of azobenzene.
Authors: Wei Zhong Lu, Chun Wei, Qui Shan Gao
Abstract: Polymethylene bis(p-hydroxybenzoates) were prepared from methyl p-hydroxybenzoate and different diols by melted transesterification reaction. Three liquid crystalline polyesters were synthesized from terephthaloyl dichloride and polymethylene bis(p-hydroxybenzoates). Its structure, morphology and properties were characterized by Ubbelohde viscometer, Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), polarized optical microscopy (POM) with a hot stage, and wide-angle X-ray diffraction (WAXD). Results indicated that the intrinsic viscosities were between 0.088 and 0.210 dL/g. Optical microscopy showed that the TLCP has a highly threaded liquid crystalline texture and a high birefringent schlieren texture character of nematic phase and has wider mesophase temperature ranges for all polyesters. DSC analysis were found that the melting point (Tm), isotropic temperature (Ti) of TLCPs decreased and the temperature range of the liquid crystalline phase became wider with increased number of methylene spacers in the polyester. The WAXD results showed that TLCPs owned two strong diffraction peaks at 2θ near 19° and 23°.
Authors: Xu Ying Liu, Wen Guang Wang, Jia Ling Pu
Abstract: Due to hexa-peri-hexabenzocoronene (HBC)’s perfect structural and their promising electronic and optoelectronic properties, the novel derivatives of HBC have continuously attracted interest. Hexaphenylbenene, as a necessary precursor to synthesize HBC, is affected by the substituents during dehydrocyclization. New synthetic strategy of some HPC derivatives with long-chain ester groups is described. Their structures were established by 1H nuclear magnetic resonance (1HNMR) and infrared spectrometry (IR), ultraviolet-visible spectrograph (UV-vis). The results indicate that the substituents play an important role on oxydehydrogenation of HPCs.
Authors: Yang Yang, Ke Qing Zhao, Wen Hao Yu, Bi Qin Wang, Ping Hu
Abstract: Series of semi-fluorinated chain liquid crystals with [1,2,3]-triazole rings have been synthesized with CuI-Et3N catalyzed alkyne-azide cycloaddition reaction. The selectively produced 1,4-disubstituted regioisomers were characterized by using IR, NMR, and Mass. The mesomorphic behaviors were characterized with polarizing optical microscopy and differential scanning calorimetry. Compounds with perfluorinated chains have showed smectic A phase.
Authors: Chung Jung Chen, Chung K. Lai
Abstract: A new type of 3,3'-(2-hydroxypropane-1,3-diyl) bis(azan-1-yl-1-ylidene)bis(2-(4-alkoxy phenyl)prop-1-en-1-ol) and their copper complexes were prepared and mesomorphic properties characterized. The mesomorphic properties of these copper complexes were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and powder X-ray diffraction. X-ray structural crystallographic analysis showed that these bimetallic compounds have two copper centers coordinated with central square planar geometry. These molecules all have total two 1a or five alkoxy sidechains 1b appended around the central core. The mesomorphic behavior exhibited was found to be dependent on the sidechain density. All compounds in 1a exhibited smectic mesophases, however, compounds in 1b exhibited hexagonal columnar phases (Colh), which were characterized by optical textures and confirmed by powder x-ray diffraction.
Authors: Xiao Dong Chen, Nan Qiao Zhou, Hai Zhang
Abstract: A thermotropic liquid crystalline polyurethane (LCPU) was synthesized by the polyaddition reaction of 3,3'-dimethyl-4,4'-biphenylene diisocyanate (TODI) with 4,4-bis(6-hydroxyhexoxy)biphenyl (BHHBP). The liquid crystalline behavior of the polymer was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD). The LCPU exhibited a nematic phase with a threaded texture and had a wide mesophase temperature range. And thermogravimetric analysis (TGA) indicated the decomposition temperature of the LCPU was >300°C. The observation of POM showed that the LCPU was a thermotropic nematic liquid crystalline polymer at certain temperature range.
Authors: Ming Tao Run, Xiao Min Hu, Mei Bo Sun, Wei Tao Ma
Abstract: The poly(4-hydroxybenzoate) (PHBA) oligomer was synthesized by using the monomer of 4-acetoxybenzoic acid (PABA), and its blends with poly(trimethylene terephthalate) (PTT) are prepared by melt-blending at 250oC in nitrogen. Their chemical structure characterization and crystal morphology were investigated by using the fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1HNMR), and polarizing optical microscopy, respectively. The results suggest that PHBA oligomer with 3 polymerization degree was synthesized and it is a thermotropic liquid crystal with the nematic characteristics. When the blends crystallize from melt, because the rigid oriented PHBA molecules becomes the nucleating agents for PTT molecules’ crystallization, much transcrystalline layers formed in the blends, although the crystalline PTT/PHBA blends show spherulites morphology character without observing nematic LC phase.

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