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G R Luckhurst - One of the best experts on this subject based on the ideXlab platform.
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on Orientational Order in nematic and twist bend nematic phases a 2h nmr study of binary mixtures of the odd dimer 1 9 bis 4 cyanobiphenyl 4 yl nonane cb9cb and the monomer 4 pentyl 4 cyanobiphenyl 5cb d2
Liquid Crystals, 2018Co-Authors: G R Luckhurst, Bakir A. Timimi, Neil J Wells, Herbert ZimmermannAbstract:In this article, we explore those factors that influence the Orientational Order in both nematic and twist-bend nematic phases. The systems used for our NMR experiments are binary mixtures of a dim...
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twist tilt and Orientational Order at the nematic to twist bend nematic phase transition of 1 9 bis 4 cyanobiphenyl 4 yl nonane a dielectric 2 h nmr and calorimetric study
Physical Review E, 2015Co-Authors: Beatriz Robleshernandez, Nerea Sebastian, Rosario M De La Fuente, D O Lopez, S Diezberart, J Salud, Blanca M Ros, D A Dunmur, G R LuckhurstAbstract:The nature of the nematic-nematic phase transition in the liquid crystal dimer 1″,9″-bis(4-cyanobiphenyl-4'-yl) nonane (CB9CB) has been investigated using techniques of calorimetry, dynamic dielectric response measurements, and (2)H NMR spectroscopy. The experimental results for CB9CB show that, like the shorter homologue CB7CB, the studied material exhibits a normal nematic phase, which on cooling undergoes a transition to the twist-bend nematic phase (N(TB)), a uniaxial nematic phase, promoted by the average bent molecular shape, in which the director tilts and precesses describing a conical helix. Modulated differential scanning calorimetry has been used to analyze the nature of the N(TB)-N phase transition, which is found to be weakly first Order, but close to tricritical. Additionally broadband dielectric spectroscopy and (2)H magnetic resonance studies have revealed information on the structural characteristics of the recently discovered twist-bend nematic phase. Analysis of the dynamic dielectric response in both nematic phases has provided an estimate of the conical angle of the heliconical structure for the N(TB) phase. Capacitance measurements of the electric-field realignment of the director in initially planar aligned cells have yielded values for the splay and bend elastic constants in the high temperature nematic phase. The bend elastic constant is small and decreases with decreasing temperature as the twist-bend phase is approached. This behavior is expected theoretically and has been observed in materials that form the twist-bend nematic phase. (2)H NMR measurements characterize the chiral helical twist identified in the twist-bend nematic phase and also allow the determination of the temperature dependence of the conical angle and the Orientational Order parameter with respect to the director.
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a deuterium nuclear magnetic resonance investigation of the symmetry and Orientational Order of the nematic phase of 4 3 4 5 tris 4 dodecyloxybenzyloxy benzoyloxy 4 4 dodecyloxybenzoyloxy 1 1 biphenyl a biaxial nematic
Journal of Chemical Physics, 1997Co-Authors: J R Hughes, Bakir A. Timimi, G R Luckhurst, Gerd Kothe, J Malthete, M E Neubert, I Shenouda, M TittelbachAbstract:The first compound for which the previously predicted biaxial nematic phase was claimed is 4-[3,4,5-tris(4-dodecyloxybenzyloxy)benzoyloxy]-4′-(4-dodecyloxybenzoyloxy)-1, 1′-biphenyl (I). This assignment was based on the observation of the optical texture and the x-ray diffraction pattern. To confirm this identification of the biaxial nematic phase, we have studied the deuterium nuclear magnetic resonance (NMR) spectra of nonuniformly aligned samples with the deuterons located specifically in the mesogen itself or in the disklike solute, hexamethylbenzene-d18, dissolved in the mesogen. These experiments allow us to determine the biaxiality in the partially averaged quadrupolar tensor. For both systems, the biaxiality parameter is found to be zero within the experimental error which is estimated to be less than ±0.08 for the pure mesogen and ±0.06 for the solute. The Orientational Order parameters determined from the quadrupolar splitting change discontinuously at the nematic-isotropic transition thus confi...
Nerea Sebastian - One of the best experts on this subject based on the ideXlab platform.
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twist tilt and Orientational Order at the nematic to twist bend nematic phase transition of 1 9 bis 4 cyanobiphenyl 4 yl nonane a dielectric 2 h nmr and calorimetric study
Physical Review E, 2015Co-Authors: Beatriz Robleshernandez, Nerea Sebastian, Rosario M De La Fuente, D O Lopez, S Diezberart, J Salud, Blanca M Ros, D A Dunmur, G R LuckhurstAbstract:The nature of the nematic-nematic phase transition in the liquid crystal dimer 1″,9″-bis(4-cyanobiphenyl-4'-yl) nonane (CB9CB) has been investigated using techniques of calorimetry, dynamic dielectric response measurements, and (2)H NMR spectroscopy. The experimental results for CB9CB show that, like the shorter homologue CB7CB, the studied material exhibits a normal nematic phase, which on cooling undergoes a transition to the twist-bend nematic phase (N(TB)), a uniaxial nematic phase, promoted by the average bent molecular shape, in which the director tilts and precesses describing a conical helix. Modulated differential scanning calorimetry has been used to analyze the nature of the N(TB)-N phase transition, which is found to be weakly first Order, but close to tricritical. Additionally broadband dielectric spectroscopy and (2)H magnetic resonance studies have revealed information on the structural characteristics of the recently discovered twist-bend nematic phase. Analysis of the dynamic dielectric response in both nematic phases has provided an estimate of the conical angle of the heliconical structure for the N(TB) phase. Capacitance measurements of the electric-field realignment of the director in initially planar aligned cells have yielded values for the splay and bend elastic constants in the high temperature nematic phase. The bend elastic constant is small and decreases with decreasing temperature as the twist-bend phase is approached. This behavior is expected theoretically and has been observed in materials that form the twist-bend nematic phase. (2)H NMR measurements characterize the chiral helical twist identified in the twist-bend nematic phase and also allow the determination of the temperature dependence of the conical angle and the Orientational Order parameter with respect to the director.
Herbert Zimmermann - One of the best experts on this subject based on the ideXlab platform.
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on Orientational Order in nematic and twist bend nematic phases a 2h nmr study of binary mixtures of the odd dimer 1 9 bis 4 cyanobiphenyl 4 yl nonane cb9cb and the monomer 4 pentyl 4 cyanobiphenyl 5cb d2
Liquid Crystals, 2018Co-Authors: G R Luckhurst, Bakir A. Timimi, Neil J Wells, Herbert ZimmermannAbstract:In this article, we explore those factors that influence the Orientational Order in both nematic and twist-bend nematic phases. The systems used for our NMR experiments are binary mixtures of a dim...
Bakir A. Timimi - One of the best experts on this subject based on the ideXlab platform.
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on Orientational Order in nematic and twist bend nematic phases a 2h nmr study of binary mixtures of the odd dimer 1 9 bis 4 cyanobiphenyl 4 yl nonane cb9cb and the monomer 4 pentyl 4 cyanobiphenyl 5cb d2
Liquid Crystals, 2018Co-Authors: G R Luckhurst, Bakir A. Timimi, Neil J Wells, Herbert ZimmermannAbstract:In this article, we explore those factors that influence the Orientational Order in both nematic and twist-bend nematic phases. The systems used for our NMR experiments are binary mixtures of a dim...
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a deuterium nuclear magnetic resonance investigation of the symmetry and Orientational Order of the nematic phase of 4 3 4 5 tris 4 dodecyloxybenzyloxy benzoyloxy 4 4 dodecyloxybenzoyloxy 1 1 biphenyl a biaxial nematic
Journal of Chemical Physics, 1997Co-Authors: J R Hughes, Bakir A. Timimi, G R Luckhurst, Gerd Kothe, J Malthete, M E Neubert, I Shenouda, M TittelbachAbstract:The first compound for which the previously predicted biaxial nematic phase was claimed is 4-[3,4,5-tris(4-dodecyloxybenzyloxy)benzoyloxy]-4′-(4-dodecyloxybenzoyloxy)-1, 1′-biphenyl (I). This assignment was based on the observation of the optical texture and the x-ray diffraction pattern. To confirm this identification of the biaxial nematic phase, we have studied the deuterium nuclear magnetic resonance (NMR) spectra of nonuniformly aligned samples with the deuterons located specifically in the mesogen itself or in the disklike solute, hexamethylbenzene-d18, dissolved in the mesogen. These experiments allow us to determine the biaxiality in the partially averaged quadrupolar tensor. For both systems, the biaxiality parameter is found to be zero within the experimental error which is estimated to be less than ±0.08 for the pure mesogen and ±0.06 for the solute. The Orientational Order parameters determined from the quadrupolar splitting change discontinuously at the nematic-isotropic transition thus confi...
Beatriz Robleshernandez - One of the best experts on this subject based on the ideXlab platform.
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twist tilt and Orientational Order at the nematic to twist bend nematic phase transition of 1 9 bis 4 cyanobiphenyl 4 yl nonane a dielectric 2 h nmr and calorimetric study
Physical Review E, 2015Co-Authors: Beatriz Robleshernandez, Nerea Sebastian, Rosario M De La Fuente, D O Lopez, S Diezberart, J Salud, Blanca M Ros, D A Dunmur, G R LuckhurstAbstract:The nature of the nematic-nematic phase transition in the liquid crystal dimer 1″,9″-bis(4-cyanobiphenyl-4'-yl) nonane (CB9CB) has been investigated using techniques of calorimetry, dynamic dielectric response measurements, and (2)H NMR spectroscopy. The experimental results for CB9CB show that, like the shorter homologue CB7CB, the studied material exhibits a normal nematic phase, which on cooling undergoes a transition to the twist-bend nematic phase (N(TB)), a uniaxial nematic phase, promoted by the average bent molecular shape, in which the director tilts and precesses describing a conical helix. Modulated differential scanning calorimetry has been used to analyze the nature of the N(TB)-N phase transition, which is found to be weakly first Order, but close to tricritical. Additionally broadband dielectric spectroscopy and (2)H magnetic resonance studies have revealed information on the structural characteristics of the recently discovered twist-bend nematic phase. Analysis of the dynamic dielectric response in both nematic phases has provided an estimate of the conical angle of the heliconical structure for the N(TB) phase. Capacitance measurements of the electric-field realignment of the director in initially planar aligned cells have yielded values for the splay and bend elastic constants in the high temperature nematic phase. The bend elastic constant is small and decreases with decreasing temperature as the twist-bend phase is approached. This behavior is expected theoretically and has been observed in materials that form the twist-bend nematic phase. (2)H NMR measurements characterize the chiral helical twist identified in the twist-bend nematic phase and also allow the determination of the temperature dependence of the conical angle and the Orientational Order parameter with respect to the director.
