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We have studied the dynamics of dielectric microparticles dispersed in a nematic liquid crystal (NLC) in the presence of an external AC electric field. Investigations were performed using optical trapping technique in the cell with in-plane electrodes. It was shown that the main driving force in the bulk of the material has electrophoretic nature. It was demonstrated that the microparticle behavior strongly depends on the distance with respect to the electrode and is influenced by the dielectrophoretic force. The model, which enables estimation of the electrokinetic forces, is proposed. The forces are found from the balance with the optical trapping force. The microparticle surface charge q≈2.1×10-17 C, linear electrophoretic mobilities μ∥≈10-11 m2/(V·s),μ⊥≈7×10-12 m2/(V·s), and the NLC viscosity η≈(21.2±4.7)×10-3 Pa·s at T=40 °C are evaluated. [ABSTRACT FROM AUTHOR]

It is well established that incorporation of nanoparticles (NPs) in the structure of ferroelectric liquid crystals (FLCs) leads to a decrease in their electrooptic response time. Several approaches have been suggested to explain this effect (decrease in rotational viscosity of FLCs, ions enhanced localised electric field, dipole-dipole interaction among NPs and FLC molecules, FLC ordering). In this article, we will report the role of the voltage divider formed by the structural elements of a FLC cell based on ferroelectric liquid crystal/gold nanospheres (FLC/GNSs) dispersion in enhancement of the switching time. Using the impedance spectroscopic measurements, it was demonstrated that the dispersing of GNSs leads to the increase in the voltage drop on FLC/GNSs layer in comparison with the pristine FLC one. Consequently, the electrooptic response time of the FLC/GNSs cell is faster than that of the pristine one. However, the rotational viscosity of the FLC does not depend on the presence of the GNSs. [ABSTRACT FROM AUTHOR]

The chiroptic response of a multi-component molecular mixture [chiral smectic C (SmC) liquid crystal] modified by achiral capped gold nanorods (GNRs) has been reported. The dispersion of the GNRs (radius rGNR=5×10-9m; length L=4.5×10-8m) with two concentrations (0.1 wt. % and 0.5 wt. %) resulted in the concentration dependent change in the circular dichroism (CD) spectrum of the SmC*-GNR complex. Three effects could be responsible for the change in the chiroptic properties of the SmC* liquid crystal. The first one is the stabilization of the helical superstructure due to the GNRs. The second one is the change in the angle between the transition electric and magnetic dipole moments near the absorption bands due to the influence of the longitudinal surface plasmon resonances (LSPRs) excited in nanorods. The third effect is the induction of chiral current in gold nanorods by the chiral component of the mixture. The latter phenomenon leads to the broad CD band at the wavelength of the LSPR. [ABSTRACT FROM AUTHOR]

Low-frequency (1 mHz–100 Hz) dielectric relaxation modes were experimentally studied in ferroelectric liquid crystal (FLC)/gold nanoparticles (nanospheres and nanorods) dispersion. It was demonstrated that the dielectric spectra of nanodispersion are strongly influenced by the shape of nanoparticles. Using different formalisms of the impedance spectroscopy, three possible low-frequency relaxation processes were found in the dispersions and the pure FLC. Due to the electrical double layers (EDLs) near nanoparticles and the alignment layers, one can observe the relaxation of the EDL polarisation around the nanoparticles (Schwarz’s relaxation) and near the driving indium tin oxide (ITO) electrodes (electrode polarisation). The other possible relaxation process is interfacial polarisation (Maxwell–Wagner mode) in which the frequency is unaffected by the nanoparticles. It was shown that Schwarz’s relaxation frequency strongly depended on the shape and size of the nanoparticles. Moreover, dispersion of nanoparticles significantly reduced direct current conductivity of the FLC mixture. [ABSTRACT FROM AUTHOR]

Electrooptical effects in ferroelectric liquid crystal cells have been simulated and the calculation results have been compared with experiments. Two sets of equations have been solved numerically: (1) the dynamic equations for the director coupled with the electric current equation; (2) the Maxwell equations which allow the calculations of the optical transmission T for different polarization, wavelength and coherency of light incident onto a cell. The anisotropy of elastic, viscous and dielectric properties and arbitrary anchoring conditions have been taken into account. The experimental data on the director switching and the electroclinic effect in the Smectic C∗ phase agree quantitatively with the modeling, and novel features of these effects are discussed. [ABSTRACT FROM AUTHOR]

The motion of dielectric microparticles induced by external ac electric field, E, was investigated in the cell with in-plane stripe electrodes and filled with homeotropically aligned nematic liquid crystal. It was demonstrated that the average velocity of the microparticles depended on the third power of the electric field strength (v=μ(3)E3). The experimental results were explained by the induced charge electrophoresis. [ABSTRACT FROM AUTHOR]

The crystal structures of two polymorphs of cis‐perinone (bisbenzimidazo[2,1‐b:1′,2′‐j]benzo[lmn][3,8]phenanthroline‐6,9‐dione, Pigment Red 194) were solved from single crystals obtained solvothermally from 1,2‐dichlorobenzene or n‐butanol at 220°C. Both crystal structures (space group P21/c) derive from stacking of flat molecules arranged due to π–π interaction. The melting points of these two polymorphs are 471°C and 468°C and their respective optical bandgaps are 1.94 eV and 1.71 eV. One of the polymorphs demonstrates drift and hopping mechanisms of electric conductivity, whereas the other one is dominated by the drift conductivity. The direct current (DC) electric conductivity of the samples are 4.77 × 10−13 S m−1 and 6.84 × 10−10 S m−1 at room temperature. The significant difference in DC conductivities can be explained by the dependence of the mobility and concentration of charge carriers on the structure of the samples. [ABSTRACT FROM AUTHOR]

The hysteresis-free electro-optical switching, or so-called V-shaped, regime has been studied in a commercial ferroelectric liquid crystal (FLC) mixture having a smectic C* phase with a very small value of spontaneous polarization. The FLC was introduced into commercial EHC cells with thin aligning layers. In such cells V-shaped switching could be observed only at very low frequencies, less than 1 Hz. However, when the same material is strongly doped with a conductive impurity, its conductivity markedly increases and hysteresis-free switching is observed over a wide range of applied frequencies and voltages. Experimental results are in good agreement with computer modelling carried out as part of this work. The modelling takes into account all the important parameters of smectic C* FLC: non-polar anchoring conditions, possible bookshelf and chevron structures, the capacitance of the aligning layers and the conductivity of a FLC. The last two factors appear to be the most crucial for hysteresis-free switching in the smectic C* phase. [ABSTRACT FROM AUTHOR]

Ionothermal synthesis of carbon nitride paved the way to a new structural allotrope—polytriazine imide. In this work, we screen available precursors for pristine polytriazine imides and for their graphitic analogs narrowing it to the melamine—urea mixture as the most promising starting material. Photocatalytic activity of materials verified in reaction of benzyl alcohol oxidation to benzaldehyde, which is known to be highly requested chemical with thousands of tons of annual production. Therefore "green" and selective route of production is highly desired. Developed PTI-LiCl was tested for selective photooxidation of benzyl alcohol to benzaldehyde, demonstrating precious conversion and selectivity rates—96.3% and 91.6%, respectively after 5 hours of UV irradiation. Detailed physical-chemical characterization revealed that PTI materials possessed more ordered and highly condensed structure which grant them improved photocatalytic properties in comparison to graphitic carbon nitride polymorph. Graphical abstract represents two different lines of materials which are known to be various polymorphs of carbon nitride studied comparatively in the present work. One of them is convenient graphitized carbon nitride which is prepared from precursors (melamine, urea or thiourea) via the simple thermal treatment. Another line of materials are prepared via thermal treatment in the eutectic mixture of molten salts. The later line of materials is more active in selective photocatalytic oxidation of benzyl alcohol. [ABSTRACT FROM AUTHOR]

The structures of the red polymorph (space group P1) and the black polymorph (space group P21/c) of 4,4′‐dimethyl‐6,6′‐dichlorothioindigo were solved from single‐crystal samples. For both polymorphs, the spatial stacking of the flat molecules is driven by π‐stacking and noncovalent interactions within the layers. Spectroscopic (UV–vis, IR and photoluminescence) and thermal properties of the red polymorph were investigated experimentally. The bandgap of this polymorph was estimated as 2.08 eV at room temperature. It is demonstrated that the electric conductivity of the red polymorph follows the hopping mechanism. [ABSTRACT FROM AUTHOR]

The influence of capped gold nanospheres (GNSs) on the direct current (DC) electric conductivity ( σ D C ) of a ferroelectric liquid crystal (FLC) confined in a cell with blocking electrodes was experimentally investigated. In framework of this work, several measurement techniques of σ D C , such as dielectric and conductivity spectroscopies, were utilised. However, it was demonstrated that only the capacitive technique allowed estimating values of σ D C of both pure FLC and FLC/GNSs nanodispersion confined in the cell with blocking electrodes. The experimental results confirm the assumption that the gold nanoparticles adsorb the impurities' ions in FLC which leads to the decrease in the conductivity of the FLC layer. [ABSTRACT FROM AUTHOR]

The thresholdless, hysteresis-free V-shape electrooptical switching in surface stabilized ferroelectric liquid crystal (FLC) cells has been modeled and the results compared with experimental data. High frequency V-shape switching (at f>100  Hz) was experimentally demonstrated and simulated numerically. The key role of the capacitance C of FLC aligning layers has been underlined: thin layers with large C promote the well known bistability effect, thick layers, on the contrary, are necessary for V-shape switching. The results of modeling are in quantitative agreement with experiment. [ABSTRACT FROM AUTHOR]