Nanocomposites and nanomaterials
Sensitive liquid crystal composites for optical sensors 
Mykytyuk Z.M.1, Barylo G.I.1, Kremer I.P. 1, Kachurak Y.M.1 
Shymchyshyn O.Y.1, Ivakh M.S.1
1 Department of Electronic Engineering, Institute of Telecommunications, Radio Electronics and Electronic Engineering, Lviv Polytechnic National University. Mytropolyta Andreya str., 1, Lviv-79000, Ukraine. 
E-mail: yurii.m.kachurak@lpnu.ua

In recent years, the use of liquid crystal mixtures as sensitive elements of optical sensors is of increasing interest [1-3].
The paper presents a comparative analysis of liquid crystal cholesteric-nematic mixtures for their use as sensitive elements of gas sensors. Liquid crystalline mixtures based on nematic E7 and cholesteric impurity CB15 are considered. To determine the optimal composition of the mixture, their spectral characteristics were studied. The main bandwidths for different concentrations of optically active impurities were determined. The temperature characteristics of liquid crystal composites were measured to determine the threshold values ​​of their transition to the isotropic state and to establish stable temperature ranges for use in optical sensors.
The results of the research show that as a sensitive element of optical sensors it is advisable to use liquid crystal mixtures with CB15 impurity concentrations of 38% and 44%. Their main bandwidths are in the visible region of the spectrum of 500-600 nm. The first mixture has better temperature characteristics, but the second shows a higher sensitivity to vapors of organic matter.
Further study of mixtures can be carried out during the direct development of optical gas sensors.

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2.	Mykytyuk, Z.M., Kremer, I.P., Ivakh, M., Diskovskyi, I.S., Khomyak, S.V. Optical sensor with liquid crystal sensitive element for monitoring acetone vapor during exhalation// Molecular Crystals and Liquid Crystals. - 2021, 721(1), pp. 24–29.
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