In order to improve the performance properties of electro-optical devices based on mesogenic materials, a cholesteric liquid crystal (cholesteryl tridecylate, X-20) was doped with nanoscale fragments ...of multilayer fluorinated graphene (GrF). A stable dispersion of X-20 with GrF was obtained. It was shown that the addition of 0.02 wt% of the nanosized GrF slightly affects phase transition temperatures of the mesogen, insignificantly reducing the mesophase temperature range due to increasing of Cr–SmA and decreasing N*–Iso transition temperatures. The dielectric properties of the pure X-20 and X-20/GrF composition were investigated in the frequency range from 20 Hz to 5 MHz and within the temperature range from 303 to 373 K. It was established that the introduction of the dopant is accompanied by an increase of the absolute value of the dielectric permittivity of the composition. At the same time, for the X-20/GrF composition a significant increase of the specific ionic conductivity was observed in the range of all studied phases due to an increase of free charge carriers. At the low frequencies of the electric field, the main contribution to the loss of dielectric permittivity makes the ionic conductivity. For the pure X-20, with the frequency increase, the contribution of the ionic conductivity decreases rapidly. This leads to a serious decrease of the imaginary part of the dielectric permittivity values and at the frequency of around 20 kHz it becomes negligible. For the X-20/GrF composition, this effect can be observed at the frequency of approximately 500 kHz and the imaginary part of the dielectric permittivity increases almost 10 times. The obtained results show the real possibility to modify conductive and dielectric properties of cholesteric liquid crystal by doping it with carbon nanomaterials. This approach opens up new opportunities in creating and improving of microantennas, frequency filters and photonic crystals based on liquid crystals.
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•System of cholesteric liquid crystal (LC) with fluorinated graphene was obtained.•Effect of nanographene on conductive and dielectric properties of LC was studied.•Increase of specific ionic conductivity at Cr–SmA–N*–Iso transitions was observed.•Proposed approach opens new opportunities in non-display applications of LC.
A cholesteric liquid crystal (CLC) - cholesteryl tridecylate (X-20) was doped with nanoparticles of shungite carbon (Sh) to effectively improve some physicochemical properties of the CLC matrix for ...the further use in electronic devices. The influence of Sh (concentration of 0.005 and 0.02 wt. %) on phase transition temperatures of X-20 was studied. Addition of 0.005 wt. % of Sh shifts phase transition temperatures upward, while the concentration increase to 0.02 wt. % leads to the opposite effect. These data were taken into account during the study of dielectric properties in different phase states. The dielectric properties were studied in the frequency range from 20 Hz to 10 MHz. Only for the system X-20/Sh (0.02 wt. %), dispersion of the dielectric permittivity was observed. The dispersion was caused by the appearance of additional relaxation processes and it was substantially more extended than the classical Debye theory suggests. The results of the research show that the 'CLC - Sh nanoparticles' composites can be used as promising materials to increase the efficiency of radio electronics devices.
The effect of gold nanoparticles on the dielectric, electro-optical, and rheological properties of the ZhK-1289 liquid-crystal mixture that define the response time of liquid-crystal devices with a ...concentration range of 0.06-5 wt% was investigated in this study. A phase diagram of the obtained composites was formed demonstrating an increase in the clearing temperature and a broadening of the mesophase existence range in the case of doping nanoparticles. It was found that in the obtained dispersions there are structural rearrangements in the low concentration range leading to an increase in the lateral bending stiffness of the liquid-crystal matrix, a decrease in the response time and threshold voltage of the Freedericksz transition, and also an increase in the anisotropy of the dielectric permittivity and the refraction index. The improvement of the electro-optical performance of the liquid crystal can be caused by the nanoparticle adsorption of impurity ions, which reduces the field-screening effect in the liquid crystal. According to the results obtained in this study, the optimal values of the physical parameters of liquid-crystal composites doped with gold nanoparticles for their application in practice are achieved in a concentration range of 0.5-1 wt%.
The article presents data on the feasibility of the concept of a high-efficiency seed cleaner with the consistent use of the air flow in aspiration and the multi-tier placement of the sorting grids ...in grating mills. As a result of modeling, the directions for further improvement of air-screen seed cleaning machines have been identified: an increase in the proportion of sorting grids in the mills up to 70 ... 80% and an increase in the speed of the air flow in the channel of the pre-filter cleaning up to 8.0 m / s. Experiments have established the competence of using mathematical modeling of airflow in the pneumatic system with the use of a finite-volume method for solving hydrodynamic equations for substantiating the basic parameters of the pneumatic system.
A technology for producing a nanocomposite based on the borsiloxane polymer and aluminum oxide nanoparticles (Al2O3 NPs) has been developed. Nanocomposites containing 0.001, 0.01, and 0.1 wt% Al2O3 ...NPs have been created. It has been shown that the nanocomposite with any content of Al2O3 NPs did not lose the main rheological properties of borsiloxane. The resulting nanomaterial is capable of generating reactive oxygen species (ROS) such as hydrogen peroxide and hydroxyl radicals. The rate of ROS generation increases up to 3 times with an increase in the concentration of Al2O3 NPs. It has been shown that the nanocomposite leads to the formation of long-lived reactive protein species, and is also the reason for the appearance of such a key biomarker of oxidative stress as 8-oxoguanine in DNA. The intensity of the process increases with an increase in the concentration of Al2O3 NPs. Moreover, it was found that bacterial cells adhere to the surfaces of the nanocomposite (reduces the number of bacteria on the substrate by 39 times), and the nanocomposite can detach bacterial cells not only from the surfaces, but also from wetted substrates. The ability to capture bacterial cells is primarily associated with the properties of the polymer; they are weakly affected Al2O3 NPs. The nanocomposite is non-toxic to eukaryotic cells, the surface of the nanocomposite is suitable for eukaryotic cells for colonization. Due to unique physical properties, low cytotoxicity and antimicrobial action, this nanocomposite can be used in medicine and prosthetics.
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•A new composite based on borsilaxane and aluminum oxide NP has been obtained.•The mechanical and physicochemical properties of the composite have been studied.•Composite inhibits bacteria growth and does not affect growth of animal cells.•The antibacterial effect is probably based on the ability to damage biopolymers.•The composite can be used in the food or textile industry.
Microbial antibiotic resistance is an important global world health problem. Recently, an interest in nanoparticles (NPs) of silver oxides as compounds with antibacterial potential has significantly ...increased. From a practical point of view, composites of silver oxide NPs and biocompatible material are of interest. A borosiloxane (BS) can be used as one such material. A composite material combining BS and silver oxide NPs has been synthesized. Composites containing BS have adjustable viscoelastic properties. The silver oxide NPs synthesized by laser ablation have a size of ~65 nm (half-width 60 nm) and an elemental composition of Ag
O. The synthesized material exhibits strong bacteriostatic properties against
at a concentration of nanoparticles of silver oxide more than 0.01%. The bacteriostatic effect depends on the silver oxide NPs concentration in the matrix. The BS/silver oxide NPs have no cytotoxic effect on a eukaryotic cell culture when the concentration of nanoparticles of silver oxide is less than 0.1%. The use of the resulting composite based on BS and silver oxide NPs as a reusable dry disinfectant is due to its low toxicity and bacteriostatic activity and its characteristics are not inferior to the medical alloy nitinol.
The kinetics of adsorption of salicylic acid from aqueous solutions on microporous granular activated carbon (GAC) was studied. The high adsorption capacity of GAC for this substance was shown. ...The order of adsorption of salicylic acid and the activation energy of adsorption were determined.
Special features of structural and phase transformations during the formation of bainitic steel structure were studied. The possibilities of identifying plate (PM) and lath (LM) martensite after ...quenching, and of tempered martensite (TM) along with upper (UB) and lower (LB) bainite after tempering of quenched steel are described. The morphology and specifics of the formation of UB, LB, and TM in the steel structure were studied. The x-ray phase analysis method was used to show the possibility of identifying phases (PM, LM, residual austenite (
A
res
), TM, UP and LB) and calculating their mass fractions in steel by decomposing the reflections into components. Quenching at 950°C was shown to produce PM and LM in steel with different morphologies and dislocation densities, contents of twins and carbon concentrations in the matrix. Tempering of the quenched steel at 500°C was shown to cause the following phase transition: PM + LM +
A
res
→ UB + LB + TM + PM+ LM+ cementite. The resistance of bainitic steel to sulfide corrosion cracking underloading and to hydrogen embrittlement was assessed.
•LC composites with quantum dots CdSe/CdS and CdSe/CdS/ZnS were synthesized.•The intensity of LC fluorescence correlates with the size of doped NPs.•The composite with CdSe/CdS/ZnS QDs show the ...fastest dielectric relaxation time.•There are optimal NPs types and concentrations to achieve the best LC operational parameters.
This work is focused on synthesis of highly luminescent hybrid CdSe/CdS ”core/shell” quantum dots (QDs) with different core sizes and an additional ZnS shell. These quantum dots were doped into a nematic liquid crystal (NLC) phase to obtain new composites. According to the dielectric and femtosecond laser spectroscopy data, sizes of the QD cores and built-up additional ZnS shells are correlated with luminescence and dielectric characteristics of the ZhK-1282 and QD composites. With larger QD cores in the ZhK-1282, a decrease in dielectric relaxation frequency of the LC molecules rotating around their short axis is observed, same for the activation energy of this process. A shift to a shorter wavelength of the LC main luminescence peak and the strong luminescence quenching effect can be observed for the composites with the 2 nm QD cores. This effect is the result of nonradiative excitation energy transfer from LCs to QDs in the composite. The adhesion work values have been calculated for all the samples, alignment substances and substrates. Optimized homeotropic aligning layers with the best composite anchoring parameters have been selected both for normal glass and glass with a sputtered indium tin oxide (ITO) layer.
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•Cholesterol tridecylate LC was doped with few-layer graphite nanoflakes (GNF).•A split of SmA-N* transition was found upon the addition of GNF.•Dipole–dipole interactions of LC and ...GNF improve the electrophysical properties of cholesteric LC matrix.•The origin of the double smectic – nematic phase transition is explained theoretically.
The effect of doping a cholesteric liquid crystal – cholesterol tridecylate (X-20) with few-layer graphite fragments/nanoflakes (GNF) has been studied with the aim to search for carbon nanostructures that able to improve the performance characteristics of helicoidal liquid–crystal materials for electro-optical devices. A nonlinear effect of dopant concentration on the phase transition temperature, thermodynamics, specific ionic conductivity, and the energy of ion transitions between equilibrium positions of X-20/GNF systems has been established. A split SmA → N* transition found upon the addition of GNF, is discussed within the framework of the model of stepwise phase subtransitions (at first, the transition occurs near the nanoparticle surface, and then it takes place in the bulk of the liquid crystal). Comparison of differential scanning calorimetry data with the characteristics of dielectric permittivity and ionic conductivity let us to suggest the generality of the factors that affect both the mesomorphism features during doping of the host liquid crystal matrix with GNF, and the differences in dielectric permittivity, ionic conductivity, and activation energy between the pure X-20 and its doped systems. The observed effects in X-20/GNF systems are explained by the coexistence of two differently directed processes: 1) interaction between GNF particles, leading to their aggregation and formation of percolation networks, 2) dipole–dipole interactions between X-20 molecules and GNF particles, leading to the orientation of X-20 on flat GNFs (anchoring effect). The dominance of one process over another depends on the GNF concentration and temperature. The dipole–dipole interactions of X-20 and GNF increase the order parameter of nematic phase at the macroscopic level, thereby improving the dielectric properties of the host liquid crystal matrix.
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