The influence of the anchoring energy of a cholesteric liquid crystal (LC) with boundary surfaces on the critical thickness d & scy;of LC layer at which the cholesteric helix unwinds. For this purpose, within the framework of the continuum theory, expression for the free energy of the LC layer is obtained. It is shown that has the form of an expansion of the Landau free energy in powers of the order parameter, which is the angle of deviation of the director from the easy orientation axis. As a result, the dependence of d & scy;on the natural pitch of the cholesteric helix p0 was determined. It is shown that in the region of small values of p0 this dependence is quadratic, while in the region of large p0 it approaches linearity.
According to the significant progress in the synthesis and study of lanthanide-containing metallomesogens, a number of fundamental questions regarding the correlations between the structure, chemical composition, and functional properties of these compounds remain unresolved. The complexity of studying these objects is due to the lack of clear understanding of the mechanisms underlying their liquid-crystalline properties and photoluminescence effects. Moreover, there are limited possibilities for extensive experimental study of the influence of the central Ln(III) ion and ligands on the molecular structure and physicochemical behavior of the experimentally obtained compounds. In this article, the geometric and luminescence characteristics of mesogenic Ln(III) complexes with substituted beta-diketones and Lewis bases were examined with the help of the quantum-chemical methods and Judd-Ofelt theory. These complexes have not been studied previously using these approaches. The relationships between the positions of the molecules' lowest triplet and singlet excited states, luminescence intensity, the efficiency and directions of intramolecular energy transfer, as well as values of theoretical emission quantum yields have been explored. The simulation results demonstrate good agreement with available experimental data. The obtained information will allow to optimize the choice of the central Ln(III) ion due to ligand's environment in order to enhance the complexes' luminescence efficiency.
New potential physiologically compatible biotransport systems were obtained and characterized: microemulsions and lyotropic liquid crystals of the composition bis(2-ethylhexyl)sodium sulfosuccinate (AOT)/water/isopropyl myristate. It was shown that with an increase in the AOT content, changes in self-organization and a transition to more ordered liquid crystal structures occur. It was found that with the introduction of luminescent markers, the developed nanocarriers can be effective carriers in targeted drug delivery with a visualization effect in target cells. Solubilization of a small heme-containing protein cytochrome C in the obtained systems was studied. By modeling the conditions at the water / oil interface, the adsorption interaction of cytochrome & Scy; with the surfactant AOT was established. It was shown that the interaction of AOT and cytochrome C is affected by the presence of amino acids contained in the protein. The kinetics of mass transfer of cytochrome C through a semipermeable model membrane into physiological Ringer's solution was studied using the developed microemulsions and liquid crystalline mesophases. The concentration of the target component in the receiving medium was estimated by UV-spectroscopy. It was shown for the first time that in the case of microemulsions, the release has a two-stage nature, while for mesophases a slow prolonged release is characteristic. The obtained results can be useful in creating effective transport systems for the delivery of biologically active substances.
The formation of liquid crystalline (LC) phases in aqueous suspensions of cellulose nanocrystals (CNCs) largely depends on the geometric dimensions of the CNC particles, their concentration, polydispersity, and surface charge. Obtaining reproducible LC structures requires meticulous control over the particle production conditions that determine these properties. The objective of this work is to investigate the possibility of formation of LC phases in dilute aqueous suspensions of CNCs and the preservation of nematic and chiral nematic order in dried films. CNCs were prepared via sulfuric acid hydrolysis of filter paper. Their properties were characterized using transmission electron microscopy, polarized optical microscopy, FTIR spectroscopy, dynamic light scattering, X-ray diffraction and elemental analysis. The rheological properties of dilute CNC suspensions and the morphology of films formed from these suspensions were examined. Additionally, the effect of ultrasonic treatment on the properties of CNC suspensions was evaluated. It was found that LC phase formation begins at a CNC suspension concentration of approximately 1 wt
The phenomenon of reversible photoinduced optical anisotropy in colored organic glasses (TOSP brand mark) has been investigated. The glasses were manufactured on the basis of polymethylmethacrylate with azo dyes plasticized by dibutyl phthalate, their thickness was 5+ mm. Such materials are used for liquid crystal photoalignment. The objective of the investigation was to identify the possibility of forming photoinduced optical anisotropy in media, which thickness significantly exceeds the wavelength of visible radiation. Experimental studies were conducted by measuring the kinetics of birefringence under exposure to polarized radiation generated by a high-pressure mercury lamp and nitrogen laser LGI-21. It was found that the thick layers studied exhibit the effect of photoinduced anisotropy that is characterized by cyclic induction and erasure of birefringence when the polarization plane orientation of the activating radiation is periodically changed. The kinetics of photoinduced birefringence varies for samples with different azo dyes, which is related to the specific features of their photochemical stability and photochromic properties. For glasses based on photochemically stable azo dyes, the possibility of accumulating optical anisotropy with irradiation cycles was discovered, opening prospects for the development of bulk optical elements with three-dimensional distribution of polarization properties. The results obtained are of significant importance for the development of new optical and optoelectronic devices, including polarized optical elements, information display systems, and optical anti-counterfeiting protection.
The rheological behavior of two polymer melts, namely hyperbranched polyisobutylene H984_57 and linear polyisobutylene L389 in the region of linear viscoelasticity, is considered. The reduced curves obtained by the known temperature-time superposition method are described using the equations of a structural model. It is shown that the curves of the storage modulus G'(omega) are described by the equations of the structural model over the entire frequency range of shear oscillations. The curves of the loss modulus G''(omega) are described by the equations of the structural model over the high-frequency range and over the low-frequency range. Over the medium-frequency range, there is a wave-like plateau on the curves of the loss modulus G''(omega) , which is explained by the shear stratification of the sample into layers with different dynamic viscosity. Within the framework of a simple two-layer model, the change in the thickness of the "fast" layer with an increase in the frequency of shear oscillations is calculated. The calculated thickness of the "fast" layer, which has a low viscosity, monotonically increases with an increase in the cyclic frequency, despite the wave-like nature of the experimental curve G''(omega) in the plateau interval.
The effect of a framework of injected nanoparticles (the previously used fullerenes and carbon nanotubes, as well as novel WS2 and MoS2 nanotubes, and CoFe2O4 nanoparticles) on the surface relief of thin polyimide films with photosensitive components based on triphenylamine is presented. The variation of wetting angles depending on the sensitizer type of the polyimide matrix was determined. Spectral measurements confirming the effect of intra-molecular complex formation on the bathochromic shift of the created composite were carried out. Quantum chemical calculations, which proof the formation of intermolecular complexes in the polyimide - nanoparticle system were performed. The possibility to expand the application field of the studied sensitized polyimides was proposed. They can be used as photolayers for light modulators based on the liquid crystals. Such photolayers can act not only as photoconductors for information recording, but they are also capable to orient liquid crystal molecules in a modulating layer.
Topological defects in nematic liquid crystals represent a material system of interest for theoretical investigations, photonic applications and biosensors. Structured configurations of liquid crystals are widely used in a range of functional devices, including lenses, diffraction gratings and molecule detection sensors. In combination with external stimuli, such as magnetic field, photoalignment etc., stabilization of liquid crystal director in the bulk becomes possible. In this work, nematic liquid crystal droplets deposited on a photosensitive surface are examined. Radially symmetric orientational structure with a centered topological point defect is observed in the liquid crystal droplet deposited on an unirradiated photosensitive surface. Low optical anisotropy makes the textures and defects to the focus of the study. This radial symmetry brakes if the substrate is exposed linearly polarized light. As a result, a diametrical disclination is observed. Droplets with tunable director structure can be used as optical lenses, where the light polarization state or magnetic field can adjust the focal length and the viewing angle. Liquid crystal director configurations were modeled by using the transfer matrix method in cylindrical coordinate system. The simulated images are in a good agreement with the experimentally observed textures.
Liquid crystals were among the first materials to revolutionize display technology, transforming bulky cathode ray tubes into flat, low-power LCDs. Their unique combination of fluidity and optical anisotropy, particularly birefringence allows to control light passing through them. This ability to modulate light under external fields forms the foundation of modern electro-optic and photonic applications. This review highlights advances in liquid crystal materials, switching physics and device architectures that are transforming photonic science and engineering. Recent innovations in the field of liquid crystal photonics are reviewed, focusing on two key areas: novel switching mechanisms and advanced material platforms. Innovations include novel switching mechanisms such as those in ferroelectric nematics, microsecond electrically modified order parameter effects and molecular reorientation in photo responsive systems. Advanced material platforms like discotic, bent-core and blue-phase liquid crystals, along with nano composite engineering using metallic, dielectric and carbon nanostructures have been developed to enhance electro-optic performance. Furthermore, integration with meta surfaces, photonic crystals and silicon platforms enables compact and reconfigurate photonic systems. A concise theoretical background and mesophase wise switching framework are also first outlined to connect material properties with device functionality. Special emphasis is placed on India's contributions from Prof. Chandrasekhar's mesophase studies to modern nano structured liquid crystal hybrids demonstrating scalable, multifunctional solutions and growing global competitiveness in liquid crystal photonics.
This paper is a continuation of the work on production of water-soluble photosensitizers for photodynamic therapy and diagnostics by the introduction of biocompatible cationic groups (trimethylammonium or N,N-dimethylpiperazinyl) into the 13th position of chlorin macrocycle. Here, we propose a laboratory technology for scaling up chlorine photosensitizers with the aim of simultaneously obtaining 1000-1500 mg of pure preparations. In addition, spectral characteristics of the synthesized photosensitizers in aqueous and non-aqueous environments are presented, along with the study of their ability to generate singlet oxygen. It was found that 65 % of the molecules of the piperazinyl derivative of chlorin e6, having absorbed a quantum of light and passed into an excited state, interact with molecular oxygen dissolved in the body and produce highly reactive singlet oxygen, leading to the death of microorganisms.
The exposure of aqueous polyelectrolyte solutions functionalized with cationic azobenzene-containing surfactant to the nematic liquid crystal (LC), confined by metal grids, induces non-equilibrium dynamical processes in nematic internal ordering at the interface of anisotropic and isotropic media with characteristic times ranging from 0.2 s to 20 s. Both fast and slow dynamical processes represent reversible distortions in the initial nematic orientational structure. The distortions were accompanied by local spatial temporal variations in the brightness of the initial dark nematic optical texture (flashes or blinks). UVinduced trans-cis isomerization of azobenzene-containing surfactant led to anchoring transition at the nematic - aqueous solution interface and suppressed the flashes. Taking into account previously reported results, we proposed that fast/slow dynamical processes were caused by the collision of micellelike/surfactant-polyelectrolyte aggregates with the metal-nematic interface. The collision leads to the collapse of aggregates and to the appearance of a surface nematic LC. The presented results can be the basis for the development of novel method for identification of aggregates in aqueous solutions using nematic LCs.
The article discusses the issues related to the quantitative assessment of the effect of geometric characteristics of carbon nanostructures, their concentration and predominant orientation in the lubricating layer after shear under load on the thickness and pressure distribution. The problem of rolling with a roller sliding along a disk, which axes are crossed, was solved. Between the roller and the disc there was a layer of lubricant with additives of carbon nanostructures of various types: 0D-zero-dimensional (shungite nanocarbon, fullerene C60), 1D-onedimensional (single-walled and multi-walled carbon nanotubes), 2D-twodimensional (graphene oxide, multilayer graphite fragments and their analogues), 3D-three-dimensional (colloidal graphite). The developed mathematical model includes the basic postulates of the theories of elasticity, hydrodynamics, mesomorphism and Flory. The numerical Newton-Raphson method was used to solve the mathematical model. The algorithm developed with its help made it possible to achieve a solution with the given accuracy in 6-10 cycles. The verification of the mathematical model was carried out using the results of other authors. It is shown that the introduced orientation parameter makes it possible to refine the Dawson-Higginson model for linear contact between rubbing surfaces. The use of carbon nanostructures with onedimensional and two-dimensional surface geometry as additives allowed to predict an increase in the thickness of the lubricating layer and a decrease in contact pressures in friction pair.
The work is aimed at studying the spectral properties of heteroleptic beta-diketonate complexes of Ga(III) and Eu(III). UV/visible and fluorescence spectroscopy showed that the complexes exhibit emission in solutions and in the solid state. A solution of the Ga(III) complex in dichloromethane has a weak fluorescence (phi(fl) = 7 %) with an emission maximum at 435 nm. The value of phi(fl) for the solution of the complex with the Eu3+ ion is 3 %. In the solid state, a decrease in the fluorescence efficiency of the [GaL(2)Bipy]Cl complex is observed compared to solutions to a value of phi(fl) of 1 %. The emission efficiency of the [EuL(2)Bipy]Cl complex in solid form is significantly affected by the molecular packing effect. The spectra do not contain a band related to the S-n - S-0 electron transition of the ligands. This indicates an increase in the efficiency of energy transfer from the ligands to the Eu(III) ion with a phi(fl) value of 15 % and promotes highly monochromatic red emission of the Eu complex in the solid state. Based on quantum chemical calculations, an analysis of the nature of electronic transitions was carried out and the geometric parameters of the coordination centers of the complexes were established.
The influence of the chemical structure of a series of homo- and heterosubstituted copper phthalocyanines bearing aryloxy groups on their mesomorphism has been examined. In the first stage, we varied both the nature of the donor, oxyaryl (cumylphenoxy or naphthoxy groups) and acceptor (nitro groups or 1-benzotriazolyl fragments) substituents introduced into the copper phthalocyanine molecule. In the next stage, we functionalized the aryloxy groups with alkylsulfamoyl fragments of varying length. All compounds were preliminarily modeled using the MM+ method in the HyperChem software package, followed by calculation of the molecular parameters in the CMP ChemCard program. A positive prediction for the formation of columnar mesomorphism was established only for three copper phthalocyanines. All compounds were synthesized and studied using optical thermal polarization microscopy and differential scanning calorimetry. Decomposition of the synthesized phthalocyanines was above 250 degrees C. It was experimentally established that phthalocyanines with cumylphenoxy and nitro groups at their periphery are non-mesomorphic. Replacing nitro groups with 1-benzotriazolyl fragments imparts mesogenity with formation of a columnar phase. The presence of eight cumylphenoxy groups at the periphery of the copper phthalocyanine molecule significantly extends the temperature range of columnar mesophase. The introduction of octadecylsulfamoyl groups into aryloxy fragments decreases melting point, significantly expands the temperature range of mesophase compared to the precursor compounds and leads to a change of mesophase type from columnar to smectic.
Liquid crystals and their composites with luminescent nanoparticles represent smart materials, which provide a selective response to a set of physicochemical factors. Microfluidic devices offer new opportunities for control of properties of these materials due to wall effects and fluid dynamics in microchannels of various geometry. In this work, we studied orientation behavior and optical properties of the composite made of lyotropic liquid crystal based on tetraethylene glycol monododecyl ether and carbon dots in straight and serpentine microchannels. We compared orientation behavior and optical properties of the composite in micro-channels and "macroscopic" conditions. An additional level of organization of lyotropic liquid crystal molecules in microchannels of various geometries was revealed: in addition to an intrinsic lamellar structure, a predominantly homeotropic and planar orientation was observed in static and dynamic samples, respectively. According to modeling and experimental verification, serpentine micro-channels were found to be suitable for characterizing orientation of liquid crystal molecules. The texture of lyotropic liquid crystal in microchannel maintains after doping it with carbon dots. Intensive luminescence of the composite was observed for all microchannel geometries in the studied range of flow rates. The effects of orientation behavior of the liquid crystal media cannot be achieved outside of microfluidic channels. The observed effects offer new opportunities for developing multifunctional "lab on chip" devices to control supramolecular organization of liquid crystals with integrated nanostructural components and can be used for molecular diagnostics and biomedicine.
It is well known that the Fr & eacute;edericksz effect plays a key role in display devices that use nematic liquid crystals as the working medium. Experimental data indicate that doping a nematic mesogen with carbon nanotubes can significantly reduce the threshold voltage of the Fr & eacute;edericksz transition compared to pure liquid crystal. In this work, a continuum theory is developed to describe the electric-field-induced Fr & eacute;edericksz transition in a colloidal suspension of carbon nanotubes in a nematic liquid crystal. For the splay geometry, the equations of orientational state are obtained. These equations determine the equilibrium configurations of the liquid crystal and the impurity subsystem directors in an external electric field. An analytical expression for the threshold field of the Fr & eacute;edericksz transition is obtained. It is shown that in the suspension, the transition occurs at a lower electric voltage than in a pure nematic. An estimate of the density of surface energy of interaction between the liquid crystal molecules and the nanotubes is obtained. The proposed theory can be used to describe the orientational, optical, and dielectric responses of the suspension to an external electric field.
The synthesis of a new sulfonamide by the Diels-Alder reaction is presented. The antibacterial activity of the obtained compound has been studied. New hybrid lyotropic liquid crystal transport systems based on the obtained sulfonamide and a nonionic surfactant-decaethylene glycol monododecyl ether, have been synthesized in an aqueous medium for potential use in biomedicine. The nature of the interactions that occur during the introduction of the sulfonamide obtained in this work into supramolecular organized lyotropic media has been studied. The effect of lanthanide derivative markers and a biological product on the optical and luminescent properties of the resulting systems has been evaluated, which will allow to control the delivery and release of new drugs.
In the framework of a continuum theory, magnetic field-induced orientational transitions in a colloidal suspension of goethite nanorods in a nematic liquid crystal are described. It is shown that in a magnetic field the suspension can exist in two uniform orientational phases, which differ in the mutual orientation of the directors of the liquid crystal and goethite nanorods. In the first planar phase, both directors coincide with the direction of the external magnetic field, and in the second angular phase, the directors are deviated from the field direction. It is established that the phase transition has a threshold character and occurs when the magnetic field reaches a critical value, which is typical for Fr & eacute;edericksz transitions in classical nematics. An analytical expression for the critical field of this Fr & eacute;edericksz-like transition is obtained. The orientational structure of the suspension has been studied.
A modified Boyle model is proposed for analyzing the dielectric properties of magnetic fluids with magnetic field-induced anisotropy. Aggregates are modeled as homogeneous ellipsoids with effective parameters, where depolarization factors link the structure geometry to dielectric anisotropy. The inverse problem of determining aggregate parameters from experimental complex dielectric permittivity spectra has been solved. The model was validated using literature data for an Isopar-M-based magnetic fluid. It was found that as the volume fraction increases from 10 % to 19 %, the aggregate aspect ratio decreases from 2.5 to 1.3, indicating a transition from chain-like aggregates to thickened clusters. The model enables real-time tracking of microstructural dynamics, showing promise for developing adaptive magnetic fluid devices.
