Механіко-енергетичний факультет
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Browsing Механіко-енергетичний факультет by Author "Bordyuh, Hanna"
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Item Cubic Susceptibility and Hyper-polarizability of the Lyotropic Liquid Crystal−Viologen System(Ukr. J. Phys. 2008, Vol. 53, N 12, p.1167-1173, 2008) Bordyuh, Hanna; Polishchuk, ArkadiyNonlinear optical properties of the “lyotropic liquid crystal–viologen” system are investigated. The system shows electrochromism under the action of an external electric field. For the colored samples, the recording of dynamic holographic gratings is obtained, by using the pulse laser method. The main characteristics of a recording on such samples are studied. On their base in view of the electrooptical properties of the system, the mechanism of the recording of gratings is proposed. The recording is realized due to a change in the polarizability of the π-electron system of viologen derivatives under the action of an intense laser radiation. The main nonlinear optical parameters (n2, χ(3), γ) of the system under study are determined.Item Dynamic grating recording in lyotropic ionic smectics of metal alkanoates doped with electrochromic impurities(Elsevier, Optical Materials 31 (2009) 1109–1114, 2009) Bordyuh, Hanna; Polishchuk, ArkadiyIn this work, we investigated nonlinear-optical properties in lyotropic ionic liquid crystals (LILC) of potassium caprilate doped with electrochromic impurities (viologens). It is known that after applying a direct electric field to the LILC-viologen cells colouration of samples is observed [1]. Dynamic grating recording under the action of nanosecond pulse laser radiation was obtained for the coloured samples. We analyzed the origin of the optical nonlinearity in the investigated materials taking into account their electrochemical and electrooptical properties. To explain grating recording in LILC doped with viologens, we proposed the mechanism of photoconversion in viologen molecules.Item Electrooptical and Nonlinear Optical Properties of Lyotropic Liquid Crystals Doped with Electrochromic Viologen(Український фізичний журнал, 2012) Bordyuh, Hanna; Polishchuk, ArkadiyThis work presents the results of experimental studies of the electrooptical and nonlinear optical properties of lyotropic ionic liquid crystals (LILC) with soluted electrochromic admixtures of viologens. It is established that the Smectic A ordering of the LILC of potassium caprylate is not disrupted by the introduction of viologens. Moreover, LILC-viologen composites obtain electrochromic properties inherent to viologens, which produce colored radical cations and dimers, while reducing. The presence of radical cations and dimmers is fixed by the optical absorption spectra. It is found that, under the action of an electric field, the LILC-viologen samples form a bilayer structure consisting of a liquid crystal layer and an absorptive layer of viologen redox products (radical cations and dimers). A dynamic grating recording is realized and studied in bilayer LILC-viologen cells. It is determined that the recording takes place in the colored layer of viologen redox products. A possible mechanism of grating recording in LILC-viologen cells is proposed.Item Fast Nolinear Optical Mechanisms in Bi-Layered Cells Composed by Lyotropic Ionic Liquid Crystals with Dye and Viologen Films(Taylor & Francis Group, LLC, Mol. Cryst. Liq. Cryst., Vol. 508, pp. 296[658]–308[670], 2009, 2009) Bordyuh, HannaMechanisms of the fast optical nonlinearity are studied in two types of cells based on lyotropic ionic liquid crystals (LILC) of metal alkanoates. They are (I) bi-layer cell, which consists of a thin dye film covered by LILC, and (II) LILC with electrochromic impurity (viologen). Applying dc electric voltage to the cell II leads to adsorption of viologen redox products with formation of a thin nanosized layer on the cathode. The dynamic holographic technique with pulsed laser radiation of the nanosecond duration was used to investigate nonlinear optical properties in both types of cells. The mechanism of photoconversion of viologen redox products under strong laser radiation is proposed to explain grating recording in the cell II.Item Holographic grating recording in “lyotropic liquid crystal – viologen” system(Національний Авіаційний Університет, 2013) Bordyuh, Hanna; Polishchuk, ArkadiyThis work presents the results of nonlinear optical experiment run on the samples of lyotropic liquid crystal (LLC) with viologen admixtures. During the experiment we obtained dynamic grating recording on bilayered LLC-viologen samples and determined main characteristics of recoded gratings. It was found out that the recording takes place in a thin near-cathode coloured viologen layer. The analysis of kinetics of thermal gratings erasing showed that contribution of a thermal nonlinearity into general diffraction efficiency is negligible small. The last fact is connected with a separation of LLC-viologen samples under the action of an electric field and heat sink into the liquid crystal layer.Item Liquid crystal materials with regulated optical properties(Національний Авіаційний Університет, 2013) Bordyuh, HannaIn this work we present the results of structural and electrooptical investigations of the new-created composites based on lyotropic liquid crystals (LLC) of potassium caprylate and viologens. Provided structural analysis showed the presence of a Smectic ordering in the investigated samples and allowed to determine its main parameters. It was shown that the electrochromic properties of viologens are preserved after their solution in the liquid-crystalline matrix. They reveal themselves as a coloration of the samples under applying of an electric field and are proved by the optical absorption spectra. Also we analyzed the processes taking place in LLC-viologen composites in the case of an electric field applying.Item Mechanism of dimerization of viologens in liquid crystalline medium(Ukr. J. Phys. 2017. Vol. 62, No. 4 294-298, 2017) Bordyuh, HannaThis work presents the analysis of experimental data on electrooptical properties of viologens incorporated into the liquid crystalline medium. These data along with theoretical considerations allow specifying the mechanism, which leads to the double color change in the liquid crystal – viologen samples stipulated by the application of increasing voltage values. Specifically, it is proved that the first color change takes place due to the one-electron reduction of viologen molecules, and the second color change is caused by the dimerization between viologen molecules, which were fully reduced under the action of a voltage applied, and initial viologen molecules.Item Mechanism of dimerization of viologens in liquid crystalline medium(Національний Авіаційний Університет, 2015) Bordyuh, HannaThis work presents the analysis of experimental data on optical properties of viologens introduced to the liquid crystalline medium stipulated by the application of increasing voltage values. These data along with quantum mechanical theory allowed to specify the mechanism of dimerization of violoden molecules which leads to the colour change of the liquid crystal-viologen sample. Specifically, the dimerization of viologen molecules in liquid crystalline medium occurs due to interaction between viologen molecules, which were fully reduced under the action a voltage applied, and initial viologen molecules.Item Mechanism of optical nonlinearity in “Lyotropic Liquid Crystal-Viologen” system(2014) Bordyuh, Hanna; Polishchuk, ArkadiyIn the present work we analyze the characteristics of holographic grating recording and consider a mechanism of optical nonlinearity in the lyotropic liquid crystal (LLC) —viologen samples. Taking into account structural and electrooptical properties of the admixture molecules it is possible to suggest that the recording is realized due to the change of polarizability of -electron system of coloured viologen derivatives under the action of laser radiation. The main nonlinear optical parameters such as nonlinear refraction coefficient, cubic nonlinear susceptibility, and hyperpolarizability were calculated.Item Structure and Intermolecular Interactions in Ionic Liquid Crystals Doped with Electrochromic Viologen(Russian Journal of Physical Chemistry, Vol. 79, Suppl. 1, 2005, pp. S66–S70, 2005) Bordyuh, Hanna; Polishchuk, ArkadiyThe results of an investigation of structural and electrooptical properties of potassium caprylate lyotropic liquid crystals (LCs) doped with electrochromic viologen are presented. The samples are colored when an electric field is applied. The color deepens with the voltage applied, and relevant features appear in electronic absorption spectra. Two stages may be recognized in the processes that occur in a sample in the field. The first stage (at 2–2.5 V) involves the formation of radical cations (RCs) from viologen molecules, which makes the samples blue (two absorption bands appear at wavelengths of 395 and 610 nm in optical spectra). At the second stage (at 3.5–4 V), the radical cations are dimerized, and the sample becomes red (the spectra show bands in the region of 365 and 520 nm). Absorption in a lyotropic LC increases with the viologen concentration increasing from 1 to 2 to 4%. Small-angle X-ray scattering was measured on unoriented samples of pure potassium caprylate with thicknesses ranging from 30 μm to 1 mm. In all samples, a smectic order was observed in lyotropic ionic LC (LILC). From the X-ray scattering data, the bilayer thickness and the smectic correlation length were computed. It was inferred that viologen molecules, when present in low concentrations (1–4%), are organically incorporated into the matrix without spoiling the layer order intrinsic to the matrix.