Browsing by Author "Polishchuk, Arkadiy"

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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, Arkadiy
Nonlinear 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.
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, Arkadiy
In 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.
Electrooptical and Nonlinear Optical Properties of Lyotropic Liquid Crystals Doped with Electrochromic Viologen
(Український фізичний журнал, 2012) Bordyuh, Hanna; Polishchuk, Arkadiy
This 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.
Holographic grating recording in “lyotropic liquid crystal – viologen” system
(Національний Авіаційний Університет, 2013) Bordyuh, Hanna; Polishchuk, Arkadiy
This 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.
Mechanism of optical nonlinearity in “Lyotropic Liquid Crystal-Viologen” system
(2014) Bordyuh, Hanna; Polishchuk, Arkadiy
In 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.
Nonlinear Optical Response of Smectic Glasses Based on Cobalt Alkanoates
(Український фізичний журнал, 2012) Gridyakina, Alexandra; Polishchuk, Arkadiy
The nonlinear-optical response of anisotropic smectic glasses based on cobalt-alkanoates is studied using the method of dynamic holography. Laser-induced dynamic gratings under the action of nanosecond laser pulses are observed and analyzed for such materials. It is found that a cubic optical nonlinearity of all studied anisotropic glasses is of electronic origin in the nanosecond diapason and caused by a nonlinear polarization of cobalt-alkanoates complexes.
Novel Nanocomposite Materials Based on Mesomorphic Glasses of Metal Alkanoates: Structure and Nonlinear Optical Properties
(High Energy Chemistry, 2009, Vol. 43, No. 7, pp. 532–535, 2009) Gridyakina, Alexandra; Polishchuk, Arkadiy
Novel nanocomposite materials based on an ordered mesomorphic glass of metal alkanoates have been proposed for fast transfer and processing of optical information. Metal alkanoate salts when heated form a smectic mesophase which can be easily supercooled forming an ordered mesomorphic glass at room temperature. The glass has the structure of the smectic-A phase: electrostatic cation–anion layers alternate with bilayers of alkane chains. The mesomorphic glass is a universal matrix for organic and inorganic nanoinclusions and nanosized crystals. In this paper, the structure of the cells of the mesomorphic glasses with various inclusions and their nonlinear optical properties, which become evident upon the impact of pulsed laser radiation with an intensity of up to 5.5 MW/cm2, have been investigated.
Optical properties of mesophases and mesomorphic glasses of Co2+ alkanoates homologous series
(Proceedings of the National Aviation University. 2013. N 4 (57): 48–52, 2013) Gridyakina, Alexandra; Polishchuk, Arkadiy
The results of spectral studies of thermotropic ionic liquid crystals (TILC) of homologous series of cobalt alkanoates and their mesomorphic glasses are presented. It is shown that the dominant coordination of the cobalt ions in the investigated media is an octahedron. A significant decrease the absorption coefficient with increasing of the aliphatic chain length in the homologous series of cobalt alkanoates is caused by the decrease of the volume concentration of the cobalt cation complexes and the dipole moments of d-d-transitions.
Structural characteristics of mesophases and mesomorphic glasses of metalalkanoates
(Proceedings of the National Aviation University. 2014. N 2 (59): 82–87, 2014) Gridyakina, Alexandra; Polishchuk, Arkadiy
The structure of the mesophases and mesomorphic glasses of cobalt alkanoates homologous series was obtained. It is shown, that typical for ITLC smectic A packing of molecules (cation-anion layer between layers alkanoate chains) preserves also in a glass phase (at room temperature).
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, Arkadiy
The 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.