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Orientational Order, Molecular Organization, and Dynamics in Mixtures of Bent-Core and Rod-Shaped Mesogens: A H-2 NMR Study
No full textMixtures of a bent-core mesogen (ClPbis10BB) and a calamitic mesogen (6OO8), showing a nematic phase over the entire compositional range and one or two smectic phases (namely, SmA, SmC, or SmCA) below the nematic one over a wide concentration range, were investigated by means of 2H NMR spectroscopy, exploiting selectively deuterated isotopomers of both mesogens. The analysis of 2H NMR spectra recorded in the liquid crystalline phases on several representative mixtures gave information on the orientational order properties and the molecular organization within the phases as well as on the alignment properties upon application of a magnetic field. On the other hand, the analysis of 2H longitudinal relaxation times (T1Z and T1Q) in 6OO8- d2/ClPbis10BB mixtures and pure 6OO8-d2 allowed the influence of the bent-core mesogen on the dynamics of the calamitic one to be highlighted
Deuterium NMR evidences of slow dynamics in the nematic phase of a banana-shaped liquid crystal
No full textC-13 and H-2 NMR study of structure and dynamics in banana B-2 phase of a bent-core mesogen
No full textIn this paper, the difficulty in orienting the B-2 phase of the banana mesogen 1,3-Phenylene-bis 4-[4-(10-undecenyloxy)- benzoyloxy] benzoate ( Pbis11BB) in a relatively high magnetic field is reported based on some observations using both C-13 and H-2 NMR. H-2 NMR spectra recorded for the two labeled isotopomers of Pbis11BB in the isotropic and B-2 phases are shown here. Preliminary results on the deuteron spin-spin relaxation (T-2) data are reported at 61 MHz in order to underline the peculiar slow dynamics of banana-shaped liquid crystals (BLC), and these results are discussed in the framework of recent studies on similar BLC. The molecular structure and dynamics in the B-2 and crystalline phases are also studied by C-13 solid-state NMR techniques. The results also point to the slow dynamics in the B-2 phase of Pbis11BB. In particular, two-dimensional MAS exchange experiment has been performed to shed light on the molecular conformation structure of the five-ring banana core in the crystalline phase of Pbis11BB, and to compare with that of quantum mechanical calculations reported in the literature
H-2-NMR of the induced Chiral Phases of Acrylate-Metacrylate Liquid Crystalline Polymers
No full textIt is shown that the addition of 2 to 6 wt.%of a chiral dopant (CD) to a series of nematic copolymers (Pn) induces blue and cholesteric mesophases. The mesomorphic behaviour of various CD + Pn mixtures is investigated by polarized optical microscopy and the phase transition temperatures are determined by DSC measurements. Deuterium NMR spectra are recorded as a function of temperature within the mesophases and the spectral line shapes characteristic of different local orientational order parameters and orientational ordering processes of molecules in a magnetic field are observed depending on temperature, heating or cooling process, chiral dopant concentration, copolymer composition, and magnetic field strength
Deuterium NMR evidences of slow dynamics in the nematic phase of a banana-shaped liquid crystal
No full textExperimental evidences of the slow dynamic behaviour of a banana-shaped liquid crystal (LC) detected by means of Deuterium Nuclear Magnetic Resonance (DNMR) in its nematic phase are reported. Deuterium line-shape and line-width trends of DNMR spectra of three selectively deuterium-labelled isotopomers of 4-chloro 1,3-phenylene bis {4-4 '-(11-undecenyloxy) benzoyloxy} benzoate (ClPbis11BB) are discussed in comparison with those of a deuterated probe dissolved in ClPbis11BB, used as LC solvent. Different dynamic regimes are observed for the central and lateral aromatic rings of the probe. These experimental remarks are discussed in terms of overall and internal molecular motions
Microscopic Organization and Tilt angle in Smectic A and Chiral Smectic C* Phases: Characterization and Orientational Order by 2H-NMR and Electric Polarization Measurements
No full text’H-NMR spectroscopy is employed to investigate the orientational order, tilt angle and layers organization of the chiral smectic liquid crystal (-)-(S)-[4-(2-methylbutyloxy carbonyl) phe- nyl] 4-n-heptyl-biphenyl carboxylate-d8 (MBHB-d,) in the magnetic field. The electrooptical behaviour of this material has a150 been investigated. The results from these two different techniques show the importance of molecular conformation for the electric and structural properties of this mesogen
Orientation, Structure and Dynamics in The Higly Ordered Smectic Phases of 7BEF5 by 2H NMR
No full textPartially deuterated liquid crystalline monomers and polymers: Characterization and order by 2H-NMR
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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