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We have elaborated a theoretical approach for the description of polar nematic phases observed by Nishikawa et al. [Adv. Mater. 29, 1702354 (2017)0935-964810.1002/adma.201702354], their structures, and transitions between them. Specific symmetry contributions to the pair molecular potentials provide the molecular mechanisms responsible for the formation of proper and improper polarity on the macroscopic level. An improper antiferroelectric nematic M2 phase can arise between paraelectric nematic M1 and proper ferroelectric nematic MP in the temperature scale. The local polarization in M2 arises mostly due to the local splay deformation. The director distribution in M2 represents the conjugation of cylindrical waves with opposite splay and polarization signs. The director and polarization are parallel to the cylindrical domain axes in the middle of each cylinder but exhibit considerable (mostly radial) deformation on the periphery of each cylinder. Polarization vectors are mostly stacked antiparallel on the borders between the domains without the director disruption. The domain size decreases with the decreasing temperature, the percentage of the antiferroelectric decouplings increases, and M2 exhibits the first-order phase transition into proper ferroelectric MP. With the increasing temperature the domain size in the M2 phase increases, the domination of particular polar orientation of molecules reduces, and finally, the domain size diverges at particular temperature corresponding to the second-order phase transition from M2 to paraelectric M1. Variations of the polar and nonpolar orientational order parameters are estimated within each phase and between the phases. Our experimental and computer simulation results (also presented in the paper) fully support our theoretical findings.

In this study, we first demonstrate the synthesis of recyclable polymer beads for Cu2+ sensing based on radially aligned liquid crystal (LC) assistance. To detect metal ions in water, sensing probe monomers and polymers derived from rhodamine B were synthesized. Recyclable polymeric LC beads were prepared from LC monomers RM257 and RM105, a nonreactive mesogen of 5CB and a rhodamine B-derived monomer. Due to the assistance of radially aligned LCs, highly sterically hindered spirocyclic terminal groups of rhodamine B-derived monomers were aligned and fixed at the outer surface of liquid crystal beads. The color of the polymeric LC beads changed from light pink to deep pink after the beads were dropped into an aqueous Cu2+ solution. The results were ascribed to the spiro ring-opening mechanism. The addition of a nonreactive mesogen resulted in the porous structure of the polymeric LC beads. The high sensitivity of the Cu2+ solution using polymeric LC beads was confirmed. The fabricated polymeric LC beads were recycled by putting the polymeric LC beads into aqueous ammonia. The removal of Cu2+ from polymeric LC beads was due to the formation of [Cu(NH3)4]2+. This recyclable LC bead sensor is an easy method for the detection of metal ions in aqueous solutions. The fabricated polymeric liquid crystal beads surfaces consist of aligned rhodamine B-derived active sites possess capacity of sensing copper ions in tested solutions. The color of the beads changed to deep pink while copper ions exist in the solutions, whereas it can be easily recycled by adding aqueous ammonia, indicating the beads applied as a powerful monitoring tool.

—The properties of the aberrational pattern resulting from the self-action of the light radiation mode TEM01 in liquid-crystal systems are studied. It is found that the interference of light rays corresponding to two peaks of intensity and nonlinear phase shift leads to the formation of a system of fringes in the Fraunhofer region; their angular period is controlled by the distance between peaks. These fringes fill the entire aberrational pattern (concentric ring pattern) or only its part, depending on the type of the profile of the light-induced phase shift. The possibilities of using the properties of the aberrational pattern in the TEM01 mode for studying the light-induced reorientation of the nematic liquid crystal director are shown.

Viscoelastic nanocomposites based on a matrix of semidilute aqueous solutions of entangled wormlike (polymer-like) micelles of a cationic surfactant and aluminosilicate nanoplates of montmorillonite clay, efficiently acting as crosslinks, were prepared and studied. The produced materials represent a new type of a self-assembling nanocomposite system. The results of changes in viscoelastic properties of nanocomposites when adding clay nanoplates are well described by a proposed interaction model which implies adsorption of wormlike micelles by end-caps to the surfactant layer formed on the nanoplates surface.

Liquid crystals are of great interest in the field of nonlinear optics due to their efficient response to low intensity light fields. Here we present a new, to the best of our knowledge, mechanism of a nonlinear optical response which is observed for a dye-doped dual-frequency nematic liquid crystal. The local increase in temperature caused by the absorption of light beam in the liquid crystal medium leads to spatial variation and inversion of the sign of the dielectric anisotropy. When an alternating current electric field with a frequency close to the cross-over frequency is applied to the liquid crystal cell, the planar orientation sustains at the beam periphery, but elastic deformation occurs in the irradiation region. In the case of a dye dopant with negative absorption dichroism, a first-order orientational transition with large bistability region is obtained.

In this study, the photoinduced orientational transitions at the variation of boundary conditions in the droplets of cholesteric (chiral nematic) liquid crystal are obtained and investigated. The effect is caused by photoisomerization of the azobenzene dendrimer additive dissolved in the liquid crystal and adsorbed on its interface. A sequence of orientational transitions under low-intensity (~1 mW/cm2) ultraviolet irradiation is revealed.

Dye-doped nematic liquid-crystalline polymers exhibit much higher orientational optical response than the systems based on low-molar-mass liquid crystals. In addition, polymer materials possess the glassy state, which allows one to record their supramolecular structure. We study the effect of light field inhomogeneity on the director deformation in the geometry of Freedericksz transition and recording of corresponding phase structures. The relationship of the light beam width with the threshold light intensity and the size of the induced and recorded deformation region was determined. An influence of the beam waist radius on the polymer director relaxation time was detected. The results of numerical calculations based on the continuum theory and the independence of the enhancement factor of the optical torque on light–polymer interaction geometry agree with the experimental data.

Orientational structure transitions due to a photoinduced surface anchoring modulation were achieved and investigated in the case of NLC microdroplets placed between glycerol and solid surface. The boundary conditions at NLC-glycerol varied under the light action on the dendromer dopant containing azobenzene terminal fragments. At the same time, the NLC had a strong planar anchoring with the polyimide treated substrate. Numerical simulation of the observed orientational structures in NLC microdroplets were carried out.

Photoinduced orientational transitions in a thermotropic nematic liquid crystal caused by modulation of the boundary conditions at the water surface were observed and investigated. The initially degenerated planar anchoring of liquid crystal at the water surface becomes homeotropic under near-UV irradiation which induces photoizomerization of comb-shaped azobenzene polymer additives adsorbed from the liquid crystal to its interface with water. After irradiation, the photoinduced orientational structures spontaneously relax to the initial ones. It was shown that the orientational sensitivity to light irradiation strongly depends on the polymerization degree of azobenzene additives.

Two sequential transformations of the orientational structure in nematic liquid crystal droplets containing a dendrimer additive (nanosized macromolecules with light-absorbing azobenzene terminal moieties) under light irradiation in the UV–blue spectral range were investigated. The origin of these transitions is in the change of the boundary conditions due to photoisomerization of the dendrimer adsorbed onto the liquid crystal–glycerol interface. It was shown that the photoisomerization processes of dendrimer molecules in a liquid crystal are accompanied by a spatial rearrangement of their azobenzene moieties, which is the key point in the explanation of the observed effects.

A comparative study of optical orientation in nematic liquid crystals (NLCs) doped with a low-molar-mass bis-azobenzene dye (monomer) and a comb-shaped polymer with side fragments similar in structure to the monomer has been carried out. Both types of bis-azobenzene dopants induced a sign-alternating nonlinearity in the NLC: the positive when the angle Ψ between the light field and the director is less than a certain critical value Ψc and the negative in the opposite case of Ψc The magnitudes of the optical-torque enhancement factors due to trans- and cis-isomers (ηT and ηC), and the ratios ηT/ηC for the low- and high-molar-mass dopants are compared. The results obtained show the possibilities of increasing the orientational optical nonlinearity when passing from low-molar bis-azobenzene dye dopants to the corresponding polymers and are important for elucidating the optimal architecture of absorbing additives.

The authors studied a group of compressor units mounted on an updated fleet of electric locomotives. In the work of the authors of the analysis of the causes of decline in the reliability of compressors, the new series electric locomotives 2ES-6 «Sinara», compared with similar installations of compressed air on old series locomotives VL-10. It is shown that the major factor in reducing reliability, is changing oilings properties of materials during the operation of the compressor units. It is shown that the main factor reducing the reliability is to change the properties of lubricating materials during the operation of the compressor units.

The dynamics of the light-induced director rotation has been studied for a comb-shaped polymers in nematic phase with a small amount (0.05 wt %) of azobenzene-dye additive. The effect of temperature on the rotational viscosity and nonlinear optical response of the liquid crystalline polymers was investigated. The orientational processes occured at the beam intensity ∼0.5 W/cm2. Cooling the samples below the glass temperature results in the memory effect.

Dye-doped nematic side-chain liquid-crystalline polymers possess extraordinary large optical nonlinearity and ability to store the induced orientational deformations in a glassy state, which makes them a very promising material for photonic applications. In this study, the phase structures were generated and recorded in the bulk of a 50-&mu, m layer of a nematic liquid-crystalline side-chain polymer, containing polyacrylate backbone, spacer having five methylene groups, and phenyl benzoate mesogenic fragment. The polymer was doped with KD-1 azodye. The director field deformations induced by the light beam close to the TEM01 mode were studied for different geometries of light&ndash, polymer interaction. The phase modulation depth of 2&pi, was obtained for the 18-&mu, m spacing between intensity peaks. The experimental data were analyzed based on the elastic continuum theory of nematics. The possibility to induce and record positive and negative microlenses in the polymer bulk was shown experimentally.

The creation of metastable particle-like structures in frustrated (unwound) chiral nematic film containing light-absorbing additive is studied. It is shown that such localized structures can be generated by the thermo-optical action of a focused laser beam or arise spontaneously at a phase transition from an isotropic to a liquid crystal state. Observed axisymmetric patterns resemble cholesteric spherulites with toroidal double-twisted director-field configuration.

In this study, the beam mode conversion in a nematic liquid crystal film deposited on the end-face of a single-mode optical fibre is considered. The infrared laser radiation delivered by this fibre induces a defect structure in the initially homeotropic liquid crystal. This leads to the formation of an output light beam with the annular intensity distribution in its cross-section. The obtained beam mode maintains its transverse profile in free space and can be interpreted as an optical vortex.

We report the light beam action on the nematic liquid crystal film with a free surface. It was found that a weak light absorption by the liquid crystal substrate dramatically changes the orienting properties of the light beam; in particular, a thermal gradient field induces an umbilical defect formation.

Liquid crystals (LCs) are distinctive materials that are applicable to a wide range of disciplines, such as continuum mechanics, optics of anisotropic media, statistical physics, and crystallography. The diverse structures and eye-catching topological defects of LCs in confined geometries are affected by nematic elasticity, chirality, and surface anchoring. Herein, we report the formation and detailed configuration of cholesteric LC (CLC) microdroplets with different pitches pierced by electrospun poly(methyl methacrylate) microfibers. Two kinds of surface anchoring, namely, homeotropic anchoring at the air–CLC droplet interface and planar anchoring at the fiber–CLC droplet interface, coexist in this system. By controlling temperature and light irradiation, the system exhibits thermal- and photo-dependent LC morphological and topological evolutions. The observed structures are complemented by numerical simulations of possible director fields decorated by defects. The externally controllable CLC necklaces constitute extraordinary systems for exploring the morphology and topological defects and open a route for applications in topological remote control, nanoscience, biomedical research, and the development of devices based on topologically structured soft media.

The formation of beams with wavefront screw dislocation appeared when circularly polarized light passes through a light-induced orientation defect formed in a homeotropically oriented NLC at the surface photorefractive effect is calculated. NLCs with negative and positive low-frequency dielectric anisotropy are considered. The calculated data are compared with the results of previously performed experiments.

The generation of optical vortices in nematic liquid crystals (NLCs) due to the photorefractive effect has been studied. The vortices can appear in the NLCs with both positive and negative dielectric anisotropy. The efficiency of the Gaussian beam (TEM00) to vortex conversion approached about 30%.

The effect of light on the conformational composition of low- and high-molecular (fifth-generation dendrimer) azobenzene dyes in a nematic host is studied. The orientational optical response of the nematic liquid crystal (NLC), caused by the presence of these compounds in the nematic host, is measured. The contributions of isomers to the orientational optical torque affecting the NLC director are determined. The results obtained suggest that the increase in the optical orientation efficiency in NLCs when using high-molecular dopants instead of low-molecular ones is unrelated to the difference in their conformational composition in the light field, but is caused by deceleration of orientational motion of chromophores.

Optical orientation in transparent nematic liquid crystalline polymer (NLCP) was observed for the first time. In NLCP with dye dopant, the light-induced second-order orientation transition being an analogue of the Freedericksz transition in low-frequency fields is found. The transition threshold is ~10 μW which is lower than the threshold of the light-induced Freedericksz transition in low-molecular nematics by four orders ofmagnitude and is lower than the characteristic value for low-molecular nematics with dye dopant by two orders of magnitude.

Orientational structures in spherical-cap droplets of chiral nematic liquid crystal are investigated experimentally and numerically. The droplets under the study have homeotropic anchoring with a flat rigid substrate and either degenerated planar or homeotropic anchoring with spherical interface between the liquid crystal and the isotropic liquid. The axially symmetric skyrmion-like structures arise when the droplet size is large enough with respect to the cholesteric pitch. The influence of electric field on the orientational structures is studied.

Diffraction of the focused circularly polarized Gaussian beam passed through an undeformed homeotropic nematic liquid crystal is considered. The parameters of two coaxial Gaussian beams and two optical vortices formed behind the liquid-crystal layer are determined. The difference in the positions of foci of Gaussian beams and vortices appears in the experiment as interference ring patterns. The efficiency of the beam transformation to optical vortices is calculated.

A light beam with wavefront screw dislocation is generated using a nematic liquid crystal under a dc electric field. Axisymmetric deformation of the director field required for the formation of such a beam appears due to light-induced removal of dc field screening by surface electric charges.

It is demonstrated that an optical beam acquires a component with spiral dislocation of wave front (optical vortex) due to passage through a layer of homeotropically aligned nematic liquid crystal with light-absorbing admixture. The vortex is formed owing to the heating of liquid crystal and transition to isotropic phase in the irradiated region, which leads to the generation of axisymmetric field distribution of director at the interface of the isotropic channel and nematic liquid crystal.

Light-induced reorientation of the dye-doped liquid-crystal polymer director is found and studied. The director rotates from the light field direction, which corresponds to the negative optical nonlinearity. The nonlinearity coefficient is several times larger than that of a low-molecular liquid crystal doped with the same dye.

Visualization of the phase object with the use of a phase-contrast scheme incorporating a nonlinear Zernike filter was carried out. A liquid crystal or liquid crystalline polymer doped with azobenzene dye inducing orientational optical nonlinearity was used as the filter. Inversion of the image contrast depending on the angle of incidence of the light beam on a nematic liquid crystal cell was implemented.

Light-induced director orientation of polymeric liquid-crystalline systems was investigated. The materials under study were composed of a nematic liquid-crystalline polymer (NLCP) and a small amount (0.05-0.5 wt.%) of conformationally active (azobenzene) or stable (anthraquinone) dye impurity. Light action on the homogeneously aligned polymer films above glass transition temperature leads to the director reorientation and, consequently, to a change in the extraordinary refractive index. The effect is associated with the dye molecule excitation and related change of intermolecular forces. In the case of NLCP with conformationally active dye dopant, an extremely high orientational optical response was detected (nonlinear coefficient is n_{2}∼0.1cm^{2}/W). In contrast, the efficiency of orientational light action on NLCP with conformationally stable dye dopant is of the same order of magnitude as that of dye-doped low-molar-mass liquid crystals. At the normal light incidence on the NLCP doped with azo-dye, the threshold director orientation is observed which is similar to the Fréedericksz transition under the action of magnetic and electric fields. The obtained high-orientational optical response of NLCP caused by azo-dye dopant in combination with the possibility of the recording of deformed structure in the glassy state, typical for polymer compounds, reveals new opportunities in photonics applications.

The orienting effect of light on nematic liquid crystals (NLCs) doped with comb-shaped polymers with different spatial distributions of side absorbing azobenzene fragments, i.e., a homopolymer (containing only azofragments), a block copolymer (containing additionally a block of non-absorbing fragments), and a statistical copolymer (containing randomly arranged absorbing and non-absorbing fragments) is experimentally studied. The light-induced Freedericksz transition threshold for the block copolymer is two times lower than that for the homopolymer. For NLC with statistical copolymer dopant, the first-order orientation transition with an extremely wide optical bistability region is observed.

We propose a simple and effective method of liquid crystal photoalignment that does not require any preliminary treatment of the cell substrates. To this aim, a small amount (0.1 wt %) of azobenzene carboxylic acid is added into the nematic liquid crystal. After filling the liquid crystal cell, a part of the dopant molecules is spontaneously adsorbed and attached to the glass surface by hydrogen bonds. This allows one to switch the boundary conditions of liquid crystal between homeotropic and planar due to the reversible trans-cis photoisomerization.

It is proposed to apply the birefringence method to measure the threshold of the light-induced Freedericksz transition and the nonlinearity enhancement factor of nematic liquid crystals by director relaxation dynamics in the light field. A birefringence change is recorded by interference of ordinary and extraordinary components of the light beamaffecting the liquid crystal director orientation. The Freedericksz transition thresholds and nonlinearity enhancement factors are measured for the samples doped with comb-shaped polymers with various degrees of polymerization. The determined thresholds are in agreement with the results obtained by the aberrational self-action method.

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.

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.

Optical vortices were generated by means of photoinduced point defects in orientation of the nematic liquid crystal (NLC). The axisymmetric distribution of NLC director field was produced due to photorefractive effect in NLC or due to isotropic channel formation in light absorbing NLC.

The light-induced director reorientation in NLCs doped with the comb-shaped azopolymers with different degrees of polymerization (the number of chromophore groups) has been studied. The negative optical nonlinearity (a decrease in the refractive index of the extraordinary wave due to the director rotation away from the light field) was observed for all dopants. It was found that the threshold power of the Freedericksz transition decreases with the polymerization degree. The light-induced Freedericksz transition of the first order was observed for the dopants with lower degrees of polymerization.

The effects of light-induced reorientation of the director of a nematic liquid crystal doped with dendrimer are investigated experimentally. The influence of light polarisation on the firstorder orientational transition that occurs with changing the light beam power is studied. An irreversible first-order orientational transition when changing the polarisation of light is discovered and examined. A theoretical description of the observed effects is presented.

Processes of light-induced reorientation of nematic liquid-crystalline molecules induced by the addition of low concentrations (0.1–2.0 wt %) of comb-shaped polymers and carbosilane dendrimers containing azobenzene fragments are studied. When the molecular structure of the above compounds becomes more complicated, the induced orientational nonlinearity increases. The introduction of 2G and 3G dendrimers into a nematic has for the first time made it possible to visualize and study a purely optical first-order Freedericksz transition in the field of a linearly polarized wave.

It was found that the second-generation carbosilane dendrimers with statistically distributed terminal aliphatic and azobenzene fragments induce negative orientational nonlinearity in nematic liquid crystals (NLC) (the NLC director turns perpendicular to the light field, decreasing the refractive index of an extraordinary wave). The light-induced Freedericksz transition in planar oriented NLCs is the first-order orientational phase transition characterized by a wide bistability region.

Reversible orientational transitions in the droplets of a nematic liquid crystal (NLC) caused by the change of boundary conditions under the low intensity diode illumination are investigated. Photosensitivity of NLC is achieved by the addition of the dendrimer compound with azobenzene terminal groups. Two types of NLC droplets in glycerol are considered: the spherical droplets in the bulk of glycerol and the droplets laid-down onto the solid substrate. In the second case, the first order phase transition is revealed. The effects described can be useful for the development of highly sensitive chemical detectors and microsized photo-tunable optical devices.

The presence of light-absorbing dopants in nematic liquid crystals (NLCs) can induce orientation nonlinearities conditioned by the torque due to changing the intermolecular forces at dopant excitation. It was shown that large nonlinearities are caused by high-molar-mass substances (comb-shaped polymers [1] and the homodendrimers with the generation number m = 1,5 [2]) containing azobenzene chromophores. The nonlinearities induced by polymers and the dendriemer with m=5 were negative (director n rotates perpendicularly to the light field E, thus decreasing the refractive index of the e-wave) in contrast to the low-molar-mass dyes similar in structure to the azobenzene chromophores and the dendrimer with m = 1, in which case the nonlinearity sign changes with the angle between E and n.

Interaction of light and ac electric fields with a nematic liquid crystal (NLC) doped with nanosized second-generation carbosilane codendrimers containing terminal azobenzene fragments has been studied. A first-order Freedericksz transition in the linearly polarized light, accompanied by an intrinsic bistability in a wide region, was observed. An additional ac electric field decreases the light-induced Freedericksz transition threshold and narrows the bistability region. Light illumination transforms the second-order electric-field-induced Freedericksz transition to a first-order one. The width of the bistability region increases with the light wave intensity. The theory of the interaction of light and ac electric fields with the dendrimer-doped NLCs is developed taking into account an additional (with respect to the undoped nematic host) dependence of the optical torque on the angle between the director and the light field.

D-amino acid were searched in wilted tomato leaves. D-Isomers of free amino acids were not revealed by the treatment with L- and D-amino acid oxidases. The noncationic fraction of the extract contained N-malonyl-D-tryptophan and no other N-acylated amino acids. A special search for endogenous N-malonyl-D-phenylalanine gave negative results. Exogenous14C-malonate was only incorporated in one Chromatographic zone corresponding to N-malonyl-D-tryptophan. It is concluded that drought stress does not induce the appearance of D-amino acids except for D-tryptophan which is accumulated in the malonylated form.

Moscow SIA RADON has developed and tested an experimental plant for treatment of radioactive waste of the mixed type including up to 40 wt. % of incombustible components with the capacity from 50 to 80 kg/h on the base of the shaft furnace with plasma heat source. Heating furnace was provided due to the arc DC plasma torch with electric capacity from 60 to 150 kW, designed at RADON. The expenses of the electric power for plasma torch were 0.5 up to 1.5 kWh/1 kg of waste depending on their composition. Pyrolytic gas with calorific value up to 4.5–5.5 MJ/kg at an output of the furnace was received, which burning provided a necessary temperature mode in the afterburner. In the shaft furnace the mode impeding radionuclides loss with off-gases has been realized. The ablation of 137Cs from the furnace did not exceed 12%, 60Co – 2.5% and trans-uranium elements – 1% due to the shaft operation mode chosen. The treatment of radioactive waste without fluxing additives has been carried out, and the slag compound with high chemical durability has been obtained.

Director deformation in a planar nematic liquid crystal (NLC) with negative optical nonlinearity (director rotates away from the light field) has been studied. First-order orientation transition and a wide hysteresis loop were observed at changing the light intensity in the presence of an ac field that is non-perpendicular to the undistorted director of liquid crystal due to pretilt. The theory of light beam interaction with NLC under ac field was constructed.

The orientational optical nonlinearity induced in NLCs by light-absorbing carbosilane codendrimers with statistical distribution of terminal aliphatic and azobenzene fragments has been studied comparatively for different (from the second to the fourth) codendrimer generations. It was found that all the codendrimers induce the negative nonlinearity (director rotates away from the light field thus decreasing the refractive index of the extraordinary wave). The orientational response increases with the generation number. The optical bistability is manifested for NLCs doped with the codendrimers of the second and third generations.

Operations were carried out on 21 patients with torsion of epiploic appendages of the colon (sigmoid 19, ascending 1, hepatic flexure 1). This pathologic condition has no specific manifestations and occurs under the mask of other emergencies. The suggested symptom of "pain displacement" in combination with other signs allowed the correct diagnosis to be established before the operation in two thirds of patients. Patients with torsion of epiploic appendages must be subjected to an emergency operation for removal of the necrotic appendage by ligation of its vascular pedicle and its peritonization with seromuscular sutures.