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The paper presents a comparative analysis of liquid crystal cholesteric-nematic mixtures for their use as sensitive elements of gas sensors. Liquid crystal mixtures based on nematic mixture E7 and cholesteric impurity CB15 were considered. In order to determine the optimal mixture, a study of the spectral characteristics of the mixtures was carried out, and the main transmission peaks were determined for different concentrations of the optically active impurity. The temperature characteristics were measured to determine the threshold values for the transition of the mixtures to the isotropic state and stable temperature areas. As a result of the conducted research, we can state that as a sensitive element of optical sensors, it is advisable to use liquid crystal mixtures with impurity concentrations of CB15 of 38% and 44%. Their main transmission peaks are in the visible region of the spectrum of 500-600 nm. The temperature characteristics are slightly better in the 38% mixture, but we can claim a slightly higher sensitivity to organic substances in the 44% mixture. Further research of mixtures can be carried out during the direct development of optical sensors. [ABSTRACT FROM AUTHOR]

Use of a noninvasive method for the diagnosis of diabetes by determining the concentration of acetone in the air during exhalation has been suggested in the research. Optical sensor based on a mixture of cholesteric liquid crystal BLO-62 and nematic 5CB as a sensitive medium for the optical sensor of acetone vapor has been proposed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Liquid crystalline materials can be used as an active media for the new generation of planar light guides. The main characteristics which governs light-guiding and switching abilities of such devices are the spatial distributions of the refraction indices (defined via the distribution of nematic director) for the liquid crystal confined within a light-guiding pore. We aim to obtain these distributions from the molecular dynamics simulation of the liquid crystalline cell with the homeotropic boundary conditions being applied. We discuss the reorientation kinetics of the homeotropic-planar transition and obtain the equilibrium director profile upon application of the planar reorienting field. [ABSTRACT FROM AUTHOR]

We develop the method of determining the threshold voltages of a cholesteric-nematic transition which is based on the analysis of conoscopic images. To improve the measurement accuracy of the threshold voltages and to eliminate the effect of a radiation wavelength, we propose a new method which also could be efficiently used to study the influence of surface conditions on the liquid crystal texture and to obtain the additional information about the liquid crystal texture in the process of cholesteric-nematic transition. [ABSTRACT FROM AUTHOR]

In this article the investigation of the cholesteric-nematic transition in thin layers of nematic-cholesteric mixtures is carried out. Nematic-cholesteric mixtures based on a nematic matrix MLC-1 with a low concentration (up to 2%) of an optically active dopant were the object of this investigation. The dependencies of threshold voltages of focal-conic deformation and forward cholesteric-nematic transition for different thicknesses of a liquid-crystal layer are obtained. It was demonstrated that the twist effect in induced cholesterics can be considered as a simple case of a cholesteric-nematic effect in thin liquid-crystal layers. [ABSTRACT FROM AUTHOR]

We propose a technique for determining of elastic constants K22 and K33 of induced cholesterics, which is based on studies of the electro-optic characteristics of cholesteric-nematic transition, dielectric properties, and pitch of induced cholesterics. Instead of the linear approximation of experimental dependencies of the threshold fields, we propose to use the hyperbolic and parabolic approximations of experimental data to determine constants K22 and K33 with increased accuracy. [ABSTRACT FROM AUTHOR]

One of the important disadvantages of information display devices based on the cholesteric-nematic effect is a low contrast level. We propose a new constructive decision to solve this problem. The classic sandwich cell is a planar waveguide taking into account the correlation between the glass refraction index and the liquid crystal layer refraction index. Therefore, in a liquid crystal layer (at the homeotropic texture) the minimum amount of light radiation propagates along the planar waveguide and is scattered perpendicularly to the propagation direction. However, in the liquid crystal layer, the confocal texture is obtained due to a voltage change, and it leads to the light scattering. This constructive solution provides the increase in the contrast level. [ABSTRACT FROM AUTHOR]

This work is connected to investigation of frequency dependences of conductive value and dielectric conductivity of the indium-tin oxide-alignment layer-liquid crystal structure which allows to find new ways in formation of the electrically stabilized structure of liquid crystal materials for the optoelectronic devices. [ABSTRACT FROM AUTHOR]