56 research outputs found

    Light-induced instabilities in photo-oriented liquid crystal cells

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    In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate instabilities occurred, when the cell was illuminated from the reference side. The instabilities were induced both by polarized white light source and monochromatic laser beams. Static and dynamic regimes were found; for laser irradiation dynamic instability was found only in a range of polarization directions. A model, developed for monochromatic excitation, predicts that at certain thicknesses dynamic instability is forbidden. Experiments on a wedge-like cell confirmed this conclusion.Comment: to appear in Mol. Cryst. Liq. Crys

    Phase behaviors of binary mixtures composed of banana-shaped and calamitic mesogens

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    In this work, five mixtures with different concentrations of banana-shaped and calamitic compounds have been prepared and subsequently studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction on non-oriented samples. The phase sequences and molecular parameters of the binary systems are presented

    Orientational Order, Molecular Organization, and Dynamics in Mixtures of Bent-Core and Rod-Shaped Mesogens: A H-2 NMR Study

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    Mixtures 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
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