The Experts below are selected from a list of 126 Experts worldwide ranked by ideXlab platform
Junji Watanabe - One of the best experts on this subject based on the ideXlab platform.
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Smectic Mesophase behavior of dimeric compounds showing antiferroelectricity frustration and chirality
Japanese Journal of Applied Physics, 2006Co-Authors: Tatsuya Izumi, Sungmin Kang, Teruki Niori, Yoichi Takanishi, Hideo Takezoe, Junji WatanabeAbstract:We have prepared a series of dimeric compounds, mOAM5AMOm, which comprise two Schiff's base mesogens. These compounds formed three types of fluid Smectic liquid crystals. When the alkoxy tail length is short (m=4 and 6), the alkoxy tail groups mix randomly with the alkyl spacer groups, resulting in the SmCAs phase. The compounds with m longer than 14 form the SmCAb phase with a bilayer character, in which the spacer and tail groups segregate from each other and consequently two mesogenic layers (so-called bilayer) are included within a repeat unit. In such a bilayer association of twin dimers, spontaneous polarization appears in each bilayer. In this SmCAb phase, furthermore, the molecules are tilted to the layer so that chirality is spontaneously formed in addition to ferroelectricity. The structure was identified as SmCAPA type. The compounds with intermediate m of 8–12 formed the frustrated SmCAf phase with a density modulation (frustration) along the layer. On cooling from the Smectic phases, crystallization takes place for mOAM5AMOm with m=4–8, while the chiral Crblue phase with the TGB-like helical structure was clearly identified with m=14–18. The structure and properties of these exotic phases in twin dimers are described in detail.
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Smectic Mesophase properties of dimeric compounds 2 distinct formation of Smectic structures with antiferroelectric ordering and frustration
Molecular Crystals and Liquid Crystals, 2000Co-Authors: Junji Watanabe, Teruki Niori, Yoichi Takanishi, Tatuya Izumi, Masahito Zennyoji, Hideo TakezoeAbstract:Abstract We have prepared two series of dimeric compounds, which comprise the schiff's base mesogen, alkyl spacer with the carbon number of 5 and alkyl or alkoxy tail with the carbon number of m = 4∼16. In these compounds, we observed three types of Smectic liquid crystals, the single layer phase with the tail group randomly mixing with the spacer, the bilayer phase in which the segregation of the spacer and tail groups takes place and so two mesogenic layers are included within a repeat unit, the frustrated Smectic phase in which the density modulation appears along the layer as well as the layer normal. The bilayer phase was found to be antiferroelectric and the frustrated Smectic phase was considered to result from the two dimensional escape from the dipolar interaction. The phase behaviour with m and the structure and properties of each phase will be described in detail.
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Smectic Mesophase properties of dimeric compounds 1 dimeric compounds based on the mesogenic azobenzene unit
Liquid Crystals, 1995Co-Authors: Teruki Niori, Seiji Adachi, Junji WatanabeAbstract:Abstract We have studied the Mesophase behaviour and structure of certain dimeric compounds, the α,ω-bis(4-n-alkoxyazobenzene-4′-carbonyloxy)alkanes, in which two azobenzene moieties with alkoxy tails are linked by a polymethylene spacer. The effect of the length of the (CH2)n spacer was examined by preparing four series of the dimers in which the carbon number of the spacer, n, is varied from 3 to 9 while the carbon number of the terminal chain, m, is held constant at either 2, 4, 8 or 12. A marked odd-even effect typical of main chain polymers was observed, such that the transition parameters and Mesophase structures strongly depend on the odd-even parity of the carbon number of the spacer. The effect of the alkyl tail length was also examined in six series of the dimers with the other combination in which n is held constant at either 4, 5, 6, 7, 8 or 9. For the dimers with even n, a short alkyl tail tends to produce a nematic phase. Increase in the length stabilizes a Smectic A phase, but a further inc...
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a new type of main chain liquid crystal polymer derived from 4 hydroxybiphenyl 4 carboxylic acid and its Smectic Mesophase behaviour
Journal of Materials Chemistry, 1994Co-Authors: Yasukazu Nakata, Junji WatanabeAbstract:A homologous series of polymers (PHBC-n) has been prepared from 4′-hydroxybiphenyl-4-carboxylic acid and ω-bromoalkan-1-ols containing five to nine methylene units which can serve as mesogen and flexible spacer groups, respectively. The PHBC-n polymers are characterized by having two different linkage groups, ether and ester groups, to connect the biphenyl mesogen to the methylene spacer, and are classified on a new type of main-chain liquid-crystal polymer. All polymers exhibit the enantiotropic Smectic phase. The Smectic behaviour and structure were examined by differential scanning calorimetry, optical microscopic and X-ray diffraction methods, and are discussed in comparison with the corresponding date of the BB-n polyesters, which include only the ester linkage group.
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thermotropic liquid crystals of polyesters having a mesogenic 4 4 bibenzoate unit Smectic Mesophase properties and structures in dimeric model compounds
Liquid Crystals, 1993Co-Authors: Junji Watanabe, Hidehiro Komura, Teruki NiioriAbstract:Abstract In this study, we prepared a homologous series of dimeric compounds, di-BB-n These compounds have two mesogenic groups linked by a flexible methylene spacer and so can be regarded as model compounds for main chain liquid crystalline BB-n polyesters. In this dimeric system, we observed distinct odd-even effects in which the Smectic Mesophase properties and structures are significantly affected by the number of carbon atoms in the flexible spacer. The most interesting effect among them was observed for a type of Smectic phase. From detailed optical microscopy and X-ray observations, we found that the even-membered di-BB-n materials form a Smectic A while the odd-membered ones form a Smectic C2 phase. Such a distinct odd-even effect was concluded to result from the confined spatial orientation of mesogenic groups which is controlled by the conformation of the flexible spacer similar to the BB-n polymeric system.
Sergey V Dvinskikh - One of the best experts on this subject based on the ideXlab platform.
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molecular and segmental orientational order in a Smectic Mesophase of a thermotropic ionic liquid crystal
Crystals, 2018Co-Authors: Jing Dai, Boris B Kharkov, Sergey V DvinskikhAbstract:We investigate conformational dynamics in the Smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution C-13 nuclear magnetic resona ...
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15n 13c dipole couplings in Smectic Mesophase of a thermotropic ionic liquid
Applied Magnetic Resonance, 2018Co-Authors: Mario Cifelli, Valentina Domenici, Vladimir I Chizhik, Sergey V DvinskikhAbstract:Unique combination of ionic conductivity and anisotropic physical properties in ionic liquid crystals leads to new dynamic properties exploited in modern technological applications. Structural and dynamics information at atomic level for molecules and ions in Mesophases can be obtained by nuclear magnetic resonance (NMR) spectroscopy through the measurements of dipole–dipole spin couplings. While 13C–1H and 15N–1H dipolar NMR spectra can be routinely acquired in samples with natural isotopic abundance, recording 15N–13C dipolar NMR spectra is challenging because of the unfavourable combination of two rare isotopes. In the present study, an approach to measure 15N–13C dipole-dipole NMR spectra in static liquid crystalline samples with natural abundance is introduced. We demonstrate that well-resolved spectra can be recorded within 10 h of experimental time using a conventional NMR probe and a moderately strong magnetic field. The technique is applied to a thermotropic Smectic Mesophase formed by an ionic liquid with imidazolium-based organic cation.
John W Goodby - One of the best experts on this subject based on the ideXlab platform.
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a nematic to nematic transformation exhibited by a rod like liquid crystal
Physical Chemistry Chemical Physics, 2017Co-Authors: Richard J Mandle, Stephen J Cowling, John W GoodbyAbstract:A novel, highly polar rod-like liquid crystal was found to exhibit two distinct nematic Mesophases (N and NX). When studied by microscopy and X-ray scattering experiments, and under applied electric fields, the nematic phases are practically identical. However, calorimetry experiments refute the possibility of an intervening Smectic Mesophase, and the transformation between the nematic phases was associated with a weak thermal event. Analysis of measured dielectric data, along with molecular properties obtained from DFT calculations, applying the Maier–Meier relationship allowed for the degree of antiparallel pairing of dipoles in both nematic phases to be quantified. Based on the results, we conclude that the onset of the lower temperature phase is driven by the formation of antiparallel molecular associations.
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interfacial layer interactions their effects on synclinic and anticlinic Smectic Mesophase behaviour in liquid crystals
Chemical Communications, 2006Co-Authors: Stephen J Cowling, John W GoodbyAbstract:Through the use of bulky cyclic terminal groups, anticlinic Smectic C phases have been observed in 2-methylbutyl materials based on the MHPOBC motif.
A R Rennie - One of the best experts on this subject based on the ideXlab platform.
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temperature dependent Smectic Mesophase ordering in fluorocarbon side chain polyesters
Liquid Crystals, 1995Co-Authors: L M Wilson, Bernd Stuhn, A R RennieAbstract:Abstract Smectic Mesophase behaviour in perfluorooctyl side chain polyesters with hydrocarbon comonomers has been investigated by DETA and X-ray diffraction at different temperatures. The polymers show clear transitions from the solid to the fluid Mesophase and from the Mesophase to the isotropic liquid.
Teruki Niiori - One of the best experts on this subject based on the ideXlab platform.
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thermotropic liquid crystals of polyesters having a mesogenic 4 4 bibenzoate unit Smectic Mesophase properties and structures in dimeric model compounds
Liquid Crystals, 1993Co-Authors: Junji Watanabe, Hidehiro Komura, Teruki NiioriAbstract:Abstract In this study, we prepared a homologous series of dimeric compounds, di-BB-n These compounds have two mesogenic groups linked by a flexible methylene spacer and so can be regarded as model compounds for main chain liquid crystalline BB-n polyesters. In this dimeric system, we observed distinct odd-even effects in which the Smectic Mesophase properties and structures are significantly affected by the number of carbon atoms in the flexible spacer. The most interesting effect among them was observed for a type of Smectic phase. From detailed optical microscopy and X-ray observations, we found that the even-membered di-BB-n materials form a Smectic A while the odd-membered ones form a Smectic C2 phase. Such a distinct odd-even effect was concluded to result from the confined spatial orientation of mesogenic groups which is controlled by the conformation of the flexible spacer similar to the BB-n polymeric system.