Search results for " liquid crystal"
showing 10 items of 100 documents
Structure and Dynamics of Liquid Crystalline Polymers from Deuteron NMR
1983
The molecular structures of thermotropic liquid crystalline polymers, which have been synthesized systematically in recent years, are described according to the model of decoupling the molecular motions of the mesogenic groups and the polymer chain by inserting a flexible spacer. The molecular structure is related to the properties of these systems, e.g., phase transition temperatures, mesophases formed, etc. The structure and mobility of a specific side chain, liquid crystalline polyacrylate with phenyl benzoate as a mesogenic group is investigated by deuteron NMR and compared with the behaviour of low molecular weight analogues selectively deuterated at equivalent positions, i.e., at the …
Melt processing of hexa-peri-hexabenzocoronene on the water surface
2011
A discotic polycyclic aromatic hydrocarbon, hexa-peri-hexabenzocoronene, was oriented by slow cooling from the isotropic phase on a water surface as a film. For melt processing at low temperatures, an HBC derivative with long swallow-tailed alkyl side chains was chosen. The supramolecular organization in the resulting thin layer was investigated by electron microscopy. In high-resolution mode, the structural study showed large domains in which the columnar structures were oriented uniaxially with an edge-on arrangement of the hydrophobic molecules. The length of the stacks exceeded several hundred nanometers without obvious defects. The small-area analysis by TEM allowed the direct visualiz…
Characterization of a fiber-reinforced new fully aromatic liquid crystalline polymer
1998
A new rigid liquid crystalline polymer that demonstrates good mechanical and thermomechanical properties and acceptable processing temperature has been recently synthesized and characterized. The melting temperature and some thermomechanical properties do not seem, however, suitable for use in some applications at high temperature or in the presence of aggressive fluids. The use of appropriate inorganic fillers can overcome these shortcomings. In this work the new LCP, polymerized in a bench-scale apparatus, and the same sample filled with carbon fibers are characterized. The properties of the carbon fiber filled LCP are compared with those of another filled wholly aromatic commercial LCP,…
Halogen-bonded photoresponsive materials
2015
The aim of the present review is to illustrate to the reader the state of the art on the construction of supramolecular azobenzene-containing materials formed by halogen bonding. These materials include several examples of polymeric, liquid crystalline or crystalline species whose performances are either superior to the corresponding performances of their hydrogen-bonded analogues or simply distinctive of the halogen-bonded species. submittedVersion Peer reviewed
Photoresponsive ionic liquid crystals assembled: Via halogen bond: En route towards light-controllable ion transporters
2017
We demonstrate that halogen bonding (XB) can offer a novel approach for the construction of photoresponsive ionic liquid crystals. In particular, we assembled two new supramolecular complexes based on 1-ethyl-3-methylimidazolium iodides and azobenzene derivatives containing an iodotetrafluoro-benzene ring as XB donor, where the iodide anion acted as an XB acceptor. DSC and X-ray diffraction analyses revealed that the preferred stoichiometry between the XB donors and acceptors is 2 : 1, and that the iodide anions act as bidentate XB-acceptors, binding two azobenzene derivatives. Due to the high directionality of the XB, calamitic superanions are obtained, while the segregation occurring betw…
2020
Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure–property relationships of the number of alkyl chains, their position, length and structure were studied.
Synthesis of New Functionalized Discotic Liquid Crystals for Photoconducting Aplications
1996
Abstract The columnar structure of discotic liquid crystals has been shown to be well suited for electronic transport parallel to the columnar axis. To tailor the processibility and mesophase behavior of such materials, several hydroxytriphenylene derivatives were synthesized. These hydroxytriphenylenes can be converted into oligomers, networks or polymers. Further, they can be reduced to arenes which posses reactive sites for classical aromatic substitutions. A number of mixed tail triphenylene derivatives and fluorescent, low symmetry triphenylene discotic liquid crystals were synthesized and characterized.
Infrared spectroscopic study of a phenyl benzoate side group—methacrylate main chain polymeric liquid crystal
1994
Abstract The temperature dependence of the infrared dichroism of a side chain polymeric liquid crystal was investigated for two homogeneously oriented samples, one aligned with a PVA coating and the other aligned by a magnetic field. From the apparent order parameters, it was found that the rotation of the mesogenic side group was restricted. Not only the rigid part of the side group, but also the alkyl chains were found to be partly ordered. Realignment of the side groups was observed in the case of the magnetically aligned sample at the smectic-nematic transition temperature. Unlike the other absorption bands, the C˭O bond vibration band shifted to higher wavenumbers with increasing tempe…
Structure formation in doped discotic polymers and low molar mass model systems
1992
Abstract Doping of low molar mass materials or polymers, possessing disc-like units, with electron acceptors leads to the stabilization of columnar discotic phases or even to the induction of such phases in compounds which either display a nematic discotic phase or only an amorphous phase in the absence of the electron acceptor. The induced columnar phase corresponds frequently to a hexagonally ordered one. We have observed, however, in addition the induction of new columnar phases such as the rectangularly ordered (Dro) and the columnar nematic phase (Nc). The enhancement of the tendency towards the formation of columnar phases is a consequence of electron acceptor—electron donor complex f…
Discotic liquid crystals at the air water interface
1991
The monolayer properties of two types of discotic liquid crystals, hexasubstituted triphenylenes 1 and azo derivatives of phloroglucinol 5, were examined. First investigations show that these discotic liquid crystals form stable monolayers. It could be shown that electron acceptors insert into the monolayer of 1. Azo discs display a packing behaviour at the monolayer that is ascribed to a side-on packing of the molecules.