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Liquid-crystalline Materials (liquid-crystalline + material)
Selected Abstracts3,5-Disubstituted Isoxazolines as Potential Molecular Kits for Liquid-Crystalline MaterialsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2009Aline Tavares Abstract A collection of 3,5-disubstituted isoxazolines have been synthesized by 1,3-dipolar [3+2] cycloaddition reactions. Some isoxazolines were selected and transformed into liquid crystals. These new liquid crystals exhibit nematic and smectic C mesophases. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Fabrication of a Superhydrophobic Surface from a Smectic Liquid-Crystal Defect ArrayADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Yun Ho Kim Abstract A novel fabrication method is developed for the preparation of superhydrophobic surfaces. The procedure uses focal conic structures of semi-fluorinated smectic liquid crystals (LCs) whose periodic toric focal conic domains (TFCDs) are prepared on a surface modified substrate. Reactive ion etching (RIE) on the periodic TFCD surface leads to a superhydrophobic surface with a water contact angle of ,160° and a sliding angle of ,2° for a 10,µL water droplet. The results show that this phenomenon is due to the development of a dual-scale surface roughness arising from the nanoscale protuberance caused by applying the RIE process to the top of the microscale TFCD arrays. The unique surface behavior is further verified by demonstrating that RIE on a flat lamellar liquid crystal film, in which the director is aligned parallel with surface, results in a relatively low hydrophobicity as compared to when periodic TFCDs are subjected to REI. The observations made in this publication suggest that a new approach exists for selecting potential candidates of superhydrophic surface formation based on spontaneous self-assembly in smectic liquid-crystalline materials. [source] EPR studies of the dynamics and phase behaviour of dithiadiazolyl radicals derived from mesogenic precursorsMAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2009Jeremy M. Rawson Abstract A series of liquid-crystalline materials based on 4-substituted cyanobiphenyls, RC6H4C6H4CN (R = C5H11, C6H13, C7H15, C8H17 and C12H25, commonly referred to as 5CB, 6CB, 7CB, 8CB and 12CB, respectively) were functionalised to give the corresponding dithiadiazolyl organic radicals RC6H4C6H4CNSSN, (compounds 1,, 2,, 3,, 4, and 5,, respectively). EPR spectra of n -C12H25C6H4C6H4CNSSN, (5,) reveal that it adopts a dimeric diamagnetic structure in the solid state with a small number of paramagnetic defect sites. Variable temperature electron paramagnetic resonance (EPR) studies reveal a thermally activated rotation about the molecular long axis at temperatures above 314 K. The energy barrier to rotation about the phenylene,dithiadiazolyl bond was estimated as 25 kJ mol,1 using density functional theory (DFT). At elevated temperatures thermal annealing was also observed, quenching the sample's paramagnetism. Copyright © 2008 John Wiley & Sons, Ltd. [source] Distinct Columnar and Lamellar Liquid Crystalline Phases Formed by New Bolaamphiphiles with Linear and Branched Lateral Hydrocarbon ChainsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2008Marko Prehm Dr. Abstract A universal building block for the convergent synthesis of a wide variety of different T-shaped ternary amphiphiles was developed and used for the synthesis of a series of new liquid-crystalline materials composed of a rigid biphenyl core with polar glycerol groups at both ends and linear or branched alkyl chains in a lateral position. In addition, compounds with bulky achiral (2,4,6-trimethylphenoxy, adamantane-1-carboxylate, benzoate) or chiral (menthyl or cholesteryl) substituents attached to the end of the lateral alkyl chain were also investigated. In all cases the lateral chains were connected to the aromatic core by an ether linkage. The effect of the ether linking unit on mesophase stability and mesophase type is discussed with respect to conformational effects. The liquid-crystalline phases were investigated by polarizing microscopy, calorimetry, and X-ray diffraction of surface aligned samples. Upon enlarging the lateral chains a series of different polygonal cylinder phases was observed, which were replaced by lamellar phases and a non-cylinder hexagonal columnar phase by further increasing the size of these substituents. Remarkably, only pentagonal, hexagonal, and giant hexagonal cylinder phases could be observed, whereas mesophases composed of cylinders with a smaller number of sides are missing. No distinct chirality effects were observed for the menthyl- and cholesteryl-substituted compounds. However, the rodlike shape of the polycyclic cholesteryl core leads to a unique phase structure combining an organization of the alicyclic cholesteryl cores perpendicular to the layer planes and the aromatic biphenyl cores parallel to the layer planes. [source] | ||||||||||