Search results for "Liquid Crystal"

Tristriazolotriazines: Luminescent Discotic Liquid Crystals

2018

Synthesis and Characterization of Fluorescent, Low-Symmetry Triphenylene Discotic Liquid Crystals:  Tailoring of Mesomorphic and Optical Properties

1996

A series of monofunctionalized triphenylene-based discotic liquid crystals were synthesized starting from 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene. These compounds are unique in that they possess a single electron-withdrawing group (and consequently a large dipole moment) connected directly to the polyaromatic core. All of the new liquid crystals show a significantly broader range of mesogenicity relative to the parent compound 2,3,6,7,10,11-hexakis(pentyloxy)triphenylene. Moreover, some of the new mesogens exhibit a more ordered mesophase relative to the hexagonal columnar phase (Dh) at lower temperatures. Monofunctionalization of the triphenylene core has a dramatic effect on…

Naturally occurring polyphenols as building blocks for supramolecular liquid crystals – substitution pattern dominates mesomorphism

2021

A modular supramolecular approach towards hydrogen-bonded liquid crystalline assemblies based on naturally occurring polyphenols is reported. The combination of experimental observations, crystallographic studies and semi-empirical analyses of the assemblies provides insight into the structure–property relationships of these materials. Here a direct correlation of the number of donor OH-groups as well as their orientation with the mesomorphic behavior is reported. We discovered that the number and orientation of the OH-groups have a stronger influence on the mesomorphic behavior of the supramolecular assemblies than the connectivity (e.g. stilbenoid or chalconoid) of the hydrogen bond donor…

Inhibition of the precipitation of barium salts in sodium dodecyl sulfate/0.1 M HCl/n-pentanol microemulsions and liquid crystals

1989

Abstract The phase ternary diagram of the sodium dodecyl sulfate (SDS)/0.1 M HCl/n-pentanol system is studied. Three monophase regions were observed: water rich and n-pentanol rich microemulsions, and a liquid crystal. These media have a strong ability to control the rate of crystal growth of barium sulfate and barium dodecyl sulfate, the precipitation being totally inhibited in the liquid crystal region.

Photoconductivity in Discotic Liquid Crystals: A New Class of High-Mobility Materials

1994

Abstract Using a time-of-flight technique, different transport mechanisms, deep trapping, multiple shallow trapping and Gaussian transport, can be observed in the different temperature and phase regions of the liquidcrystalline (LC) photoconductor hexapentyloxytriphenylene (HPT). Transient photocurrents and carrier mobilities for various temperatures, electric fields, and sample histories were examined. The ideal intrinsic Gaussian transport, observed for holes in the mesophase, puts HPT into a new class of highmobility materials with both hole mobilities on the order of 1.10−3cm2/Vs and a steplike current decay. These features result from the fact that there is obviously neither a position…

Confinement effects on the interactions of native DNA with Cu(II)-5-triethyl ammonium methyl salicylidene orto-phenylendiiminate in C12E4 liquid crys…

2008

Confinement effects of native calf thymus DNA interacting with the complex Cu(ii)-5-(triethylammoniummethyl)salicylidene ortho-phenylendiiminate (CuL(2+)) perchlorate in tetraethylene glycol monododecyl ether (C(12)E(4)) liquid crystals have been investigated by UV absorption spectrophotometry, circular dichroism (CD) and small angle X-ray scattering (SAXS). The results indicate the occurrence of dramatic structural changes of both the DNA and the CuL(2+)-DNA system, when going from aqueous solution to C(12)E(4) liquid crystals, due to confinement constrains imposed by the closed structure of C(12)E(4) reverse micelles. Further marked departures from the behaviour observed in aqueous soluti…

Electrohydrodynamic instabilities and orientation of dielectric ellipsoids in low-conducting fluids.

2000

We study the dynamics of an ellipsoidal particle in a weakly conducting dielectric liquid when submitted to a dc electric field. At low field intensities, the particle long axis is aligned in the field direction. When the field strength is increased, we show that, depending on the initial orientation of the particle, there exist two stable orientations: the one with the long axis parallel to the field direction remains possible while a spinning state with the long axis perpendicular to the field appears. This last striking orientation is due to the finite Maxwell-Wagner polarization relaxation time. For sufficiently high field intensities, each state loses its stability and the particle dyn…

Fluctuating Interfaces in Liquid Crystals

2008

We review and compare recent work on the properties of fluctuating interfaces between nematic and isotropic liquid-crystalline phases. Molecular dynamics and Monte Carlo simulations have been carried out for systems of ellipsoids and hard rods with aspect ratio 15:1, and the fluctuation spectrum of interface positions (the capillary wave spectrum) has been analyzed. In addition, the capillary wave spectrum has been calculated analytically within the Landau-de Gennes theory. The theory predicts that the interfacial fluctuations can be described in terms of a wave vector dependent interfacial tension, which is anisotropic at small wavelengths (stiff director regime) and becomes isotropic at l…

Computer simulation study of a liquid crystal confined to a spherical cavity.

2007

The interplay of surface ordering and elasticity can be studied on the example of a liquid crystal confined to a cavity. We present a computer simulation study of a liquid of hard spherocylinders in a hard spherical cavity. With increasing density, first a uniaxial surface film forms and then a biaxial surface film, which eventually fills the entire cavity. We studied how the surface order, the adsorption, and the shape of the director field depend on the curvature of the wall. We find that orientational ordering at a curved wall is stronger than at a flat wall, while adsorption is weaker. For densities above the isotropic-nematic transition, we always find bipolar configurations.

Textures in hexatic films of nonchiral liquid crystals: Symmetry breaking and modulated phases

1994

Novel modulated textures, such as stripes and multiarmed star defects, have been observed in freely suspended films of nonchiral liquid crystals just below the smectic-$C$ to hexatic phase transition. Detailed studies using depolarized reflection microscopy suggest that the stripes are locally chiral surface splay domains of the smectic-$L$ phase, a tilted hexatic not previously identified in thermotropic liquid crystals. Line defects which form additional domain walls in the hexatic lattice lead to characteristic modulations of the basic one-dimensional stripe pattern. Inside thick circular islands, for example, stripes form circumferentially and the lines form centered 12-armed stars, res…