2D diffraction gratings were prepared by polymerization-induced fixation of electrohydrodynamic convection patterns in a nematic mixture. Photo- and electro-optical tuning of their diffraction efficiency was demonstrated.
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Stimuli responsive liquid crystalline polymers are a unique class of so‐called “smart” materials demonstrating various types of mesomorphic structures easily controlled by external fields, including light. In the present work we... more
Stimuli responsive liquid crystalline polymers are a unique class of so‐called “smart” materials demonstrating various types of mesomorphic structures easily controlled by external fields, including light. In the present work we synthesized and studied a comb‐shaped hydrazone‐containing copolyacrylate exhibited cholesteric liquid crystalline properties with the pitch length of the helix being tuned under irradiation with light. In the cholesteric phase selective light reflection in the near IR spectral range (1650 nm) was measured and a large blue shift of the reflection peak from 1650 nm to 500 nm was found under blue light (428 or 457 nm) irradiation. This shift is related to the Z‐E isomerization of photochromic hydrazone‐containing groups and it is photochemically reversible. The improved and faster photo‐optical response was found after copolymer doping with 10 wt % of low‐molar‐mass liquid crystal. It is noteworthy that both, the E and Z isomers of hydrazone photochromic group are thermally stable that enable to achieve a pure photoinduced switch without any dark relaxation at any temperatures. The large photoinduced shift of the selective light reflection, together with thermal bistability, makes such systems promising for applications in photonics.
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Among the various types of liquid crystalline (LC) structures, the cholesteric mesophase attracts special attention in view of helical supramolecular structure determining their specific optical properties. The helix pitch of cholesteric... more
Among the various types of liquid crystalline (LC) structures, the cholesteric mesophase attracts special attention in view of helical supramolecular structure determining their specific optical properties. The helix pitch of cholesteric liquid crystals is very sensitive to mechanical stress, resulting in change of their optical properties and position of selective light reflection peak. Here, films of polymer‐dispersed cholesteric liquid crystals based on polyurethane elastomer are prepared and studied. Liquid crystal mixtures based on chiral cholesterol derivatives are uniformly dispersed in the form of micrometer‐sized droplets in an elastomeric matrix. A significant mechano‐optical response of the composites under the action of deformation is demonstrated, and the change in the position of the selective light reflection band during mechanical stress is studied in detail. A shift in the selective light reflection peak by 100 nm or more is found. This process is accompanied by color transformations of brightly colored films. Such materials can be promising for creating stress and deformation sensors, ripple and bending sensors, and other technical devices.
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... A. YU. BOBROVSKY, NI BOIKO and VP SHIBAEV* Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119899 Russia ... 1. Introduction explained by the transition of the spiro form of such compounds into the merocyanine... more
... A. YU. BOBROVSKY, NI BOIKO and VP SHIBAEV* Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119899 Russia ... 1. Introduction explained by the transition of the spiro form of such compounds into the merocyanine form [1113]: ...
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... A. YU. BOBROVSKY, NI BOIKO and VP SHIBAEV* Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119899 Russia ... 1. Introduction explained by the transition of the spiro form of such compounds into the merocyanine... more
... A. YU. BOBROVSKY, NI BOIKO and VP SHIBAEV* Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119899 Russia ... 1. Introduction explained by the transition of the spiro form of such compounds into the merocyanine form [1113]: ...
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Research Interests: Materials Science, Optics, Chemistry, Library Science, Crystallography, and 14 morePhotochromism, Exhibition, Atlanta, Wavelength, Radical, Dopant, Liquid Crystal, Diamagnetism, Ferromagnetism, Nanostructured Carbon Electrodes, Screen Printed Electrodes, Lamellar Structure, Antiferromagnetism, and Paramagnetism
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The Zernike method using a nematic liquid crystal (NLC) filter with orientational optical nonlinearity was applied to visualize phase objects. It was shown that the contrast sign of the image switches by means of varying the incidence... more
The Zernike method using a nematic liquid crystal (NLC) filter with orientational optical nonlinearity was applied to visualize phase objects. It was shown that the contrast sign of the image switches by means of varying the incidence angle of a light beam on liquid crystal cell. The comparison of a contrast sign change of opaque object in the schemes based on NLC-filter and on liquid filter with thermal optical nonlinearity was performed.
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A new experimental approach to multiparametric three-dimensional (3D) investigation of a broad class of composite nanostructural materials is developed on the basis of scanning near-field optical nanotomography (SNONT). Using this method,... more
A new experimental approach to multiparametric three-dimensional (3D) investigation of a broad class of composite nanostructural materials is developed on the basis of scanning near-field optical nanotomography (SNONT). Using this method, it is possible to simultaneously study the optical properties, 3D morphology, and distribution of the mechanical and electrical properties of the same region of a sample. The proposed method combines features of the confocal and near-field optical microspectroscopy (fluorescence and Raman spectroscopy) with a lateral resolution of up to 50 nm and scanning-probe microscopy. The possibility of studying the volume distribution of optical, morphological, electrical, and mechanical characteristics of a material with nanoscale resolution is related to the probing of sequential layers at a step of up to 20 nm and a total Z-scan depth of up to 3 mm. In particular, the SNONT method has been used to study a liquid-crystalline polymer doped with fluorescent nanocrystals.
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ABSTRACT We report complex optical investigations of polymer-stabilised cholesteric photonic liquid crystal doped by a dichroic fluorescent dye. For the first time, we employed a combination of various experimental methods, including... more
ABSTRACT We report complex optical investigations of polymer-stabilised cholesteric photonic liquid crystal doped by a dichroic fluorescent dye. For the first time, we employed a combination of various experimental methods, including measurements of spectra of transmission, reflection, rotation of the plane of polarisation of light, fluorescence, to characterise the properties of the photonic crystal. The peculiarity of the reported investigations is employing a photosensitive cholesteric mixture forming the photonic crystal. The position of the photonic band could be changed by illumination with ultraviolet light and stabilised by thermopolymerisation. In this way, the position of the cholesteric band was matched with the emission band of the fluorescent dye, which enabled to perform diversified studies on the same photonic crystal. We determined the parameters, which defined the optical properties of the photonic crystal, spectral dependence of the transformation of linearly polarised light to elliptically polarised as the light passes the photonic crystal, the photonic density of states. The interpretation of the experimental data was performed using analytical expressions obtained from the solution of Maxwell’s equations, numerical calculations by the Berreman matrix method. Graphical Abstract
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New types of hybrid liquid crystalline composites based on organic and inorganic matrices were elaborated and their unique photooptical properties were demonstrated.
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One of the most actual tasks in biotechnology is the creation of a new generation of nanobiosensors with improved brightness, photo stability, and sensitivity. Compositions of polymers and colloidal quantum dots (QDs) are the most... more
One of the most actual tasks in biotechnology is the creation of a new generation of nanobiosensors with improved brightness, photo stability, and sensitivity. Compositions of polymers and colloidal quantum dots (QDs) are the most promising base to develop such sensors. This work presents the technology for creation and detailed analysis of nanostructured composite films based on polypropylene matrices with uniformly distributed CdSe/ZnS quantum dots and liquid crystals. Methods of optical microscopy, scanning probe microscopy and confocal fluorescent microspectroscopy were used. The presence of liquid crystals in the composite allows additional control of QDs fluorescence. The methodology proposed is applicable not only to polypropylene, but also to other porous polymers. The results of this work indicate the possibility of creating high-quality polymer/QDs composite materials and open the way to the development of nanomaterials (nanosensors) with optical properties sensitive to va...
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ABSTRACT High sensitivity of liquid crystals to the electric field makes them highly demanded and widely used in different applications. Despite the large number of the electro-optical research on the low-molar-mass liquid crystals... more
ABSTRACT High sensitivity of liquid crystals to the electric field makes them highly demanded and widely used in different applications. Despite the large number of the electro-optical research on the low-molar-mass liquid crystals electro-optics of the liquid crystalline (LC) polymers is much less studied. Herein, the comparative electro-optical behaviour of two nematic comb-shaped polyacrylates with phenylbenzoate mesogenic side groups was studied in detail. These two polyacrylates have completely the same structure of polymer backbone and spacer length but different in the direction of the ester group in the phenylbenzoate fragments. It was found that this difference predetermines their completely opposite electro-optical properties. The influence of the electric field of different strength and frequency on the orientation of the mesogenic groups of these polymers is studied. It is shown that application of the electric field at temperatures above the glass transition temperature (~25°C) induces reorientation of the mesogenic groups along or perpendicular to the electric field direction depending in its turn on the ester group direction. For one of the polyacrylates an unusual textural transition is found; during cooling of the polymer sample under applied field at definite temperature a sharp change in the mesogen’s orientation from homeotropic to planar one is found. This electro-optical phenomenon is observed for the first time and probably associated with sharp change in sign of anisotropy of dielectric permittivity from positive (at high temperatures) to negative one (at lower temperatures). Kinetics of the electro-optical switching at different temperatures, influence of the molar masses of the polymer and frequency of the applied AC field on electro-optical behaviour of the polymers are studied. The possibility of the fixation of the electroinduced homeotropic alignment of the mesogenic groups by photopolymerisation of the diacrylate dissolved in the polymer is demonstrated. Graphical Abstract
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Research Interests: Materials Science, Medicine, Polymer, Physical, Dopant, and 2 moreLiquid Crystal and Azobenzene(Liquid Crystal and Azobenzene)
(Liquid Crystal and Azobenzene)
Optical nonlinearity of nematic liquid crystalline polymer caused by molecular reorientation was found and investigated. Under the action of light on the polymer film, director of polymer reorients to light field increasing the refractive... more
Optical nonlinearity of nematic liquid crystalline polymer caused by molecular reorientation was found and investigated. Under the action of light on the polymer film, director of polymer reorients to light field increasing the refractive index. If the polymer is doped with an azobenzene compound, nonlinear response dramatically increases; in this case, the light-induced refractive index becomes negative.
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Novel LC monomer and corresponding polymethacrylate are synthesized and their phase behaviour, photooptical properties and photoorientation under polarized-light action are studied.