Liquid Crystals and Related Materials II

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Authors: Ming Tao Run, Zi Yu Qi, Meng Yao, Wen Zhou, Bing Tao Xing
Abstract: The phase morphology and dynamic rheology of poly (trimethylene terephthalate)/maleinized poly (octene-ethylene)/organo-montmorillonite nanocomposites were investigated by using transmission electron microscopy (TEM) and rotational rheometer. The results suggest that some of the OMMT are peeled off and the nanosheets are dispersed evenly in the polymer matrix. When the OMMT content is more than 4%, they are tended to form the aggregates in nanocomposites. The nanocomposites’ melt are pseudo-plastic fluid, and both complex viscosity and shear storage modulus increase with increasing OMMT content due to the interaction between the OMMT and polymers. The nanocomposites’ melt show more elasticity behavior with more OMMT content especially at low shear frequencies.
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Authors: Ye Chen, Tie Shi Wang, Fa Qi Yu, Xin De Tang, Mei Shan Pei
Abstract: Amphiphilic block copolymers have attracted increasing attention due to their potential applications in controlled release and biotechnology. The self-assembled aggregates consisit of a hydrophobic core and hydrophilic shell to produce a vehicle suitable for delivering hydrophobic drugs. In addition, stimuli-responsive polymers can be triggered by external factors and give rise to the corresponding physical and/or chemical changes. So far reports concerning the supramolecular assembly between two or more kinds of block copolymers are limited. In this work, supramolecular assembly of binary block copolymers of PEO-b-PMAA and PEO-b-PMAZO in the selective solvent was investigated.
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Authors: Wei Biao Zhu, Hai Xiao Gan, Yuan Yuan Zhuang, Wei Min Qin, Yan Ping Wang, Yi Min Wang
Abstract: Thermotropic liquid-crystalline polymers (TLCPs) have aroused wide public concern which is attributed to their high strength, stiffness, chemical resistance and perfect dimensional stability as high-performance engineering materials. Vectran heat treated after melt spinning is a representative commercial aromatic copolyester fiber. In this study, a novel TLCP melt-polymerized with 4,4’-diphenyloxide dicarboxylic acid (DODA), 4-acetoxybenzoic acid (ABA), hydroquinone diactate (HQA), 2,6-naphthalene dicarboxylic (NDA) and terephthalic acid (TA) were melt spun into fibers and heat treated to enhance the breaking strength and Young’s modulus. Intermolecular mechanical elements slipped between 120-130 °C and crystallization or the conformational rotations occurred along the extended polymer chain. For this new TLCP fiber, the optimal heat treatment temperature was 260 °C and the suitable heat-treatment time was over 48 hours. The breaking strength, Young’s modulus and breaking elongation of the as-spun fiber were improved from 1.58GPa, 45.21GPa and 1.97% to 3.20GPa, 133.44GPa and 2.42% respectively after heat treatment.
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Authors: M. Ramakrishna Nanachara Rao, P.V. Datta Prasad, D. Madhavi Latha, V.G.K.M. Pisipati
Abstract: Synthesis, characterization and phase transition studies (Dilatometry) have been carried out on three mesomorphic Schiff base compounds viz., N-(p-n-pentyl benzylidene)-p-n-hexadecyloxy aniline, 5.O16, N-(p-n-pentyloxy benzylidene)-p-n-hexadecyloxy aniline 5O.O16 and N-(p-n-pentyl benzylidene)-p-n-hexadecyl aniline, 5.16. The liquid crystalline phase identification and the phase transition temperatures have been carried out using SDTECHS polarising microscope attached with temperature controller with accuracy of ± 0.1 °C and for the conformation of the phase identification and the textures observed are compared with the standard textures. Further, the phase transition temperatures and the corresponding heats of transition across the phase transitions are recorded using DSC (Perkin Elmer). The characterization studies reveal that these compounds exhibit NG, N and A phase variants respectively. The nature of the phase transitions are studied through density results using dilatometric technique. The phase transitions exhibit first order nature in all the cases as expected. The results are discussed in the light of the body of the data available on other Schiff base compounds and on 5O.16.
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Authors: Ru Zheng Wang, Jian Jun Liu, Hui Li Li
Abstract: In this paper, using the theories of Bogolyubov-Hellman-Feynman (BHF) and mean-spherical approximation, we get the system free energy within the four-order self-consistent cumulant expansion. According to the conditions of equilibrium state and self-consistent equation, we obtain the relation between reduced temperature and inverse correlation length and disscuss that the cubic invariant item is important in explaining BPIII to isotropic transition.
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Authors: B.R. Rajeswari, P. Pardhasaradhi, M. Ramakrishna Nanachara Rao, P.V. Datta Prasad, D. Madhavi Latha, V.G.K.M. Pisipati
Abstract: The refractive indices measurements are carried out using a modified spectrometer connected with wedge shaped cell and also the direct measurement of birefringence,δn obtained from Newton’s rings method with an indigenous setup for the liquid crystalline compounds p-n-(phenyl benzylidene)-p-n-alkyl and alkyloxy anilines, PBnA and PBnOA compounds. The molecular polarizabilitiy anisotropy (α|| - α) is calculated for these compounds from different methods such as Lippincott δ-function model, molecular vibration method, Haller’s extrapolation method and scaling methods respectively. Further, the estimation of the molecular polarizabilities αe and αo are done from the isotropic Vuks and anisotropic Neugebauer models. The order parameter directly calculated from ∆n employing the method developed by Kuczynski is compared with the order parameter estimated from the different models using molecular polarizabilities.
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Authors: Xing Fang Jiang, Shu Xin Wu
Abstract: Polymer-dispersed liquid crystals are one kind of important devices. With a He-Ne laser and a photoelectric detector, we measured the driving-voltage dependent and viewing-angle dependent transmission for a polymer-dispersed liquid crystal device. Our results showed that the polymer-dispersed liquid crystal device worked at the driving voltage of 4 V and the effective viewing angle of about 65 degree.
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Authors: Yuan Ming Huang, Qing Lan Ma, Bao Gai Zhai
Abstract: With polarizing optical microscopy we have investigated the electro-optic properties of a nematic liquid crystal 4-n-pentyl-4′-cyanobipheny confined in the microchannels of porous silicon. Experimental study shows clearly that the liquid crystal molecules tend to align parallel to the direction of the pore columns in porous silicon. Schlieren textures with S = +1 and +2 disclinations were recorded. Our experimental investigations show that uniaxial alignment, the planar radial and the escaped radial configurations exist around the given microchannels of porous silicon.
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Authors: Xin De Tang, Ye Chen, Fa Qi Yu, Mei Shan Pei
Abstract: Stimuli-responsive water-soluble and amphiphilic polymers have attracted much attention because their micelles can be produced or destroyed by changing the temperatute, pH, ionic strength, and solvent polarity. In this work, a triply hydrophilic block copolymer of poly (ethylene glycol) and poly (methacrylic acid-co-dimethylamine ethyl methacrylate) [PEO-P(MAA-co-DMAEMA)] was synthesized and characterized. The copolymer system is believed to have the potential for drug delivery applications due to the biocompatibility of MAA and DMAEMA.
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Authors: Shezan Hasware, Ratnaraaj Parekh, Anil Devlekar, S.M. Bhatia
Abstract: The mixtures of nematic [4-Hexyloxy-4-Biphenyl carbonitrile] and cholesteryl propionate were investigated at various temperatures. Measurements of refractive index and transition temperatures were noted by using an Abbe refractometer with a heating arrangement. Ordinary and extraordinary refractive indices were obtained which helped us in calculating the order parameter and its variation with temperature. We also carried out Fabry-Perot Scattering Studies (FPSS) on our samples to confirm the various transition temperatures. Photographs of liquid crystal mixture samples placed between crossed nicols are taken at various temperatures to observe the phase transition.
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