Optical Rotatory Power in the Isotropic Phase of Four Cholesteryl Esters

Recent theoretical work by numerous authors has indicated that pretransitional properties of the isotropic phase are highly dependent on the chirality of the nearby ordered phase. To test this aspect of the theories, we present results on the optical rotatory power in the isotropic phase for a series of four cholesteryl esters of varying chirality. The most important finding is that the separation between the first and second order transition temperatures decreases with an increase in chirality. However, the results of a recent experiment which claimed to present evidence for strong coupling between the structural modes of the ordered phase are not substantiated by the new measurements reported here.     

Detection of Photoemission of Electrons into Anthracene Crystals by Studying Recom ination Radiation

Evidence for photoemission of electrons from a calcium contact into anthracene crystals is presented. It is based on the observation of recombination radiation resulting from mutual annihilation of photoinjected electrons with holes which are supplied by an ohmic counter-electrode. The method avoids spurious effect's due to optical release of trapped electrons. The problem of photoemission of electrons from alkali-metals into anthracene crystals is discussed.     

Surface Order Parameter of 4-n-Heptyl-4′-Cyanobiphenyl

We measured the order parameter near the interface between a liquid crystal and the solid substrate treated by several methods. The interfacial order parameter is different according to the surface treatment, and is larger than the bulk order parameter. Moreover, in the temperature above the clearing point, the interfacial order still has a finite value.     

New Chiral Esters,Diastereomeric 2-(4-Carboxybenzylidene)-p-Menthane-3-One Derivatives,as Components of LC Systems with Induced Helical Structure

Abstract

Diastereomeric 1R, 4S- and 1R, 4R-2-carbomethoxybenzylidene-p-menthane-3-ones have been synthesized. The helical twisting power and the induced helical pitch temperature dependence have been measured for the liquid crystal mixtures based on the nematic 4-methoxybenzylidene-4′-butylaniline and 4-pentyl-4′-cyanobiphenyl containing the obtained diastereomeric chiral dopants. The distinction in the characteristics of the diastereomeric chiral dopants is discussed.     

Acid mediated tunability of stimulated laser emission from dye doped chiral microdroplets

Abstract

In the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal inside an immiscible isotropic fluid to create an emulsion. Since liquid crystals are extremely sensitive to external factors as temperature or external fields, laser tuning can be easily achieved. Here, we report on the possibility to tune the laser emission from dye doped cholesteric liquid crystals microdroplets dispersed in a glycerol matrix in presence of nitric acid molecules in the emulsion. Using a fluorescent dye with pH dependent optical properties, the emitted laser wavelength can be tuned in a range of 60?nm. This effect could find applications for the development of spectroscopy based sensors.     

Nonlocal Continuum Theory of Liquid Crystals

A nonlocal continuum theory of liquid crystals is constructed to explain and predict the physical behavior of liquid crystals under long range intermolecular forces Balance laws consist of conservation of mass and mocroinertia, balance of momenta and energy. Constitutive equations are given for the equibilibirium and non-equilibirium parts of the stress, couple strees, free energy, entropy an nonlocal body force and couple. Thermodynamic restrinctions and material frame-indifference are studied. The theory is valid for liquid crystals having arbitrary shapes (inertia), Passage is made to the thread-like molecuels and to local theory. Applications are considered to two-dimensional problmes, steady, plane shear flows and disperison of twist waves.     

Optical Rotatory Dispersion Measurements of the Liquid Crystalline Blue Phases in Thick Layers

The results of optical rotatory dispersion (ORD) measurements in liquid crystalline blue phases (BP) are reported for pure compounds and mixtures. They have been performed on polycrystalline samples (thick layers). Two features distinguish their spectra from those obtained from liquid single crystals:

(1) The magnitude of the rotation is much smaller, and

(2) no sharp anomalous ORD region is present.

The spectra possess a weak, broad anomalous region. Their sign and wavelength dependence follows the sense and pitch of the cholesteric helix. ORD experiments with mixtures of the same cholesteric esters with a nematic substance yield results typical of well oriented samples. The spectra exhibit larger rotation angles and a significantly smaller anomalous region.     

Infrared Linear Dichroism of Nematic Solutions I. Orientation of Guest Molecules in Nematic Hosts

The orientational order and the biaxiality of some mono-substituted benzenes in namatic liquid crystals have been determined from infrared linear dichroism measurements. The experimental results are in good agreement with the theoretical predictions of the mean field theory.     

Nonlinear Transport Phenomena in MX3

It was confirmed from experiments of the Hall effect that the non-linear conductivity of NbSe₃ results from depinning of CDW's. The non-linear conductivity was also observed in the monoclinic phase of TaS₃. The field dependence of the conductivity was very similar to that observed in the CDW state of NbSe₃.     

Liquid crystal material with gold nanoparticles as optical sensors active medium for the amino acids detection

Abstract

In the article, the possibility of using the cholesteric liquid crystal mixture doped by the gold nanoparticles as an active medium of optical amino acid sensors is shown. The BLO-62 and the 5CB were used as a cholesteric liquid crystal and a nematic liquid crystal correspondingly. This mixture was doped by the gold nanoparticles. The method of gold nanoparticles synthesis is considered and their parameters are determined. Studies on the spectral characteristics of the investigated materials have shown that the addition of gold nanoparticles to the system leads to a significant decreasing in the spectral characteristic steepness and give the possibility of expanding the measurement range of amino acid concentration.     

Epr Study of Polarons In a Conducting Polymer With Nondegen-Erate Ground States: asF5 Complexes of Poly(p-phenylene)

EPR measurements of temperature-dependent susceptibility and linewidth are reported for poly(p-phenylene) as a function of exposure time to dopant. Most of the charge is in bipolarons, rather than in the spin-associated polarons. Observed decreases in high temperature spin concentration as a function of doping time and post-doping anneal likely arise from both polaron-polaron reaction and polaron ionization to form bipolarons. The susceptibility of all the investigated AsF₅-doped samples strongly deviate from Curie-Weiss behavior at low temperatures. The observed temperature dependence can be explained by the low-temperature condensation of isolated polarons to form intermolecular polaron pairs in singlet ground states. The interaction between spins is antiferro-magnetic and the energy of the singlet-state polaron pair relative to two isolated polarons (-2.4 to -4.8 meV) is similar to that for the n-doped polymer (-2.4 to -2.7 meV).