Search results for "Liquid Crystal"
showing 10 items of 492 documents
Thermotropic properties and molecular packing of discotic tristriazolotriazines with rigid substituents.
2014
Tristriazolotriazines with a threefold dialkoxyaryl substitution have been prepared by Huisgen reaction of cyanuric chloride and the corresponding tetrazoles. Although these dyes show a negative or inverted solvatochromism of the UV/Vis absorption, their fluorescence is strongly positive solvatochromic. These discotic fluorophores are also emissive in their solid state and in their broad liquid-crystalline mesophase. The structural study indicates that the thermotropic properties and organization of these systems can be well tuned by the steric demand of the aryl groups. Depending on the substituents, the compounds showed either a pure crystalline phase or a highly complex helical superstru…
Self-assembly in surfactant-based mixtures driven by acid–base reactions: bis(2-ethylhexyl) phosphoric acid–n-octylamine systems
2013
Structural and dynamic features of bis(2-ethylhexyl) phosphoric acid (HDEHP)-n-octylamine (NOA) mixtures as a function of the NOA mole fraction (X-NOA) have been investigated by SAXS, WAXS, IR, dielectric spectroscopy and polarized optical microscopy. In the 0 <= X-NOA < 0.5 range, mixtures are transparent liquids, while the abrupt formation of a waxy solid characterized by an hexagonal bidimensional structure occurs at X-NOA = 0.5. Such a composition-induced phase transition results from the synergetic effect of the progressive increase in number density of ordered HDEHP-NOA nanodomains with X-NOA. Mainly driven by an HDEHP to NOA proton transfer, the increase of structural order with X-NO…
Dual-Mode Chiral Self-Assembly of Cone-Shaped Subphthalocyanine Aromatics
2020
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/jacs.0c07291
On the Structure and Chiral Aggregation of Liquid Crystalline Star‐Shaped Triazines H‐Bonded to Benzoic Acids
2020
The ability of a star-shaped tris(triazolyl)triazine derivative to hierarchically build supramolecular chiral columnar organizations through the formation of H-bonded complexes with benzoic acids was studied from a theoretical and experimental point of view. The combined study has been done at three different levels including the study of the structure of the triazine core, the association with benzoic acids in stoichiometry 1:3, and the assembly of 1:3 complexes in helical aggregates. Although the star-shaped triazine core crystallizes in a non-C3 conformation, the C3 -symmetric conformation is theoretically predicted to be more stable and gives rise to a favorable C3 supramolecular 1:3 co…
Optical Symmetry of Ferroelectric Liquid Crystal Cells
1990
We observe an exact optical symmetry in Surface Stabilized Ferroelectric Liquid Crystal (SSFLC) cells in polarized transmission optical microscopy and spectroscopy. A theoretical argument based on the intrinsic time reversibility of Maxwell's equations and energy conservation is developed to explain this symmetry. The results support the model of Clark and Rieker for zig-zag wall structure and illustrate the necessity of including the orientational binding of the director at the chevron interface.
Semiflexible Polymers in Spherical Confinement: Bipolar Orientational Order Versus Tennis Ball States
2017
Densely packed semiflexible polymers with contour length L confined in spheres with radius R of the same order as L cannot exhibit uniform nematic order. Depending on the chain stiffness (which we vary over a wide range), highly distorted structures form with topological defects on the sphere surface. These structures are completely different from previously observed ones of very long chains winding around the inner surface of spheres and from nematic droplets. At high densities, a thin shell of polymers close to the sphere surface exhibits a tennis ball texture due to the confinement-induced gradual bending of polymer bonds. In contrast, when the contour length of the chains is significant…
Fast electroclinic switching in a ferroelectric LC-polysiloxane
1992
Oxadiazolyl-Pyridinium as Cationic Scaffold for Fluorinated Ionic Liquid Crystals
2021
The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of sa…
Measurements of temperature polarization phenomena in membrane distillation channels by a thermographic technique
2014
In the present work, a recently presented experimental technique, based on the use of thermochromic liquid crystals (TLCs) and digital image processing, has been employed in order to measure the temperature and local heat transfer coefficient distribution on the membrane surface in a MD spacer-filler channel
Mesophase behaviour of 2,5-dibenzoyloxy-p-benzoquinone derivatives and tetrahydrobenzene tetraesters
1991
Abstract The synthesis of 2,5-dibenzoyloxy-p-benzoquinone derivatives, their products after reduction and tetraesters from tetrahydroxybenzene prepared from those products is described. Their phase behaviour was investigated by differential scanning calorimetry and polarizing microscopy and is discussed in terms of their detailed structure.