Vol 43, No 3 (2024)

The aggregation properties of a number of 6,6'-substituted thiacarbocyanine dyes were studied by spectral-fluorescent methods: T-304, T-306, T-307, T-336 and, for comparison, thiacarbocyanine Cyan 2, which has no substituents in the 6,6'-positions, in aqueous buffer solutions and in the presence of various types of surfactants. The method of moments was used to characterize the absorption spectra (band positions, width, shape). Substituents in the 6,6'-positions significantly increase the ability of dyes T-304, T-306, T-307, T-336 to aggregation (dimerization, as well as to the formation of disordered aggregates with broad low-intensity absorption spectra). The introduction of surfactants leads to rearrangement of the spectra associated with the complex nature of the equilibria between monomers and aggregates of various structures (including surfactant molecules, if present), in particular, with a decrease in the contribution of disordered aggregates. However, the decomposition of dimeric aggregates of 6,6'-substituted cyanines is observed only at very high surfactant concentrations (~20 CMC and higher, where CMC is the critical micelle concentration). At the same time, the passing of surfactant concentrations through CMC does not significantly affect the spectral-fluorescent properties of the dyes, which is probably due to rather strong interactions of the dyes with individual surfactant molecules and premicellar associates of surfactants.

The effect of ultraviolet radiation of various wavelengths (254 nm and 365 nm) on compositions based on polylactide with the addition of natural rubber was studied. It was found that the effect of the wavelength of 254 nm on the studied samples is much more active than 365 nm, which is characterized by a decrease in the melting temperature and the degree of crystallinity of polylactide in the compositions, as well as a deterioration in physical and mechanical properties. The IR spectroscopy method confirms the photodegradation process by changing the intensities of structurally sensitive polylactide and natural rubber bands.

The mechanism of isoolefins initiation in the presence of ethylaluminum dichloride – proton donor (water, phenol, hydrochloric acid) complex catalysts has been studied by ab initio HF.3.21G. The energetics of these reactions was estimated, the values of its activation energy and thermal effects were obtained. It was found that among the studied catalysts, an increase in the activation energy of the reaction of initiation of oligomerization of isoolefins contributes to an increase in the selectivity of the process.

The ignition of pelletized samples of hard coals of the long-flame gas (DG), gas (G), fat (L), coke (K) grades with particle sizes ≤63 μm by laser pulses (λ = 532 nm, τ_i = 10 ns) was studied. When the critical radiation energy density H_cr⁽¹⁾, specific for each grade of coal, is exceeded, an optical breakdown occurs and a dense plasma with a continuous emission spectrum is formed. As the plasma expands and rarefies, the spectra show the emission of carbon ions CII, excited nitrogen atoms N, excited carbon molecules C₂, and carbon monoxide CO. The plasma glow intensity peaks at the end of the laser pulse, and the glow relaxation time is ~1 μs. The plasma glow amplitude increases nonlinearly with increasing laser pulse energy density. At radiation energy density H ≥ H_cr⁽²⁾, specific for each grade of coal, thermochemical reactions are initiated in the volume of microparticles and coal particles are ignited in a submillisecond time interval.

Intermetallic alloys were synthesized in the 5Ti + 3Si + xNi system by the method of self-propagating high-temperature synthesis (SHS) and mechanosynthesis. The influence of nickel content on the morphology, size and yield of composite particles after mechanical activation (MA) of mixtures was studied. The dependences of the maximum temperatures and combustion rates, phase composition, morphology and elongation of synthesis products on the nickel content for the initial and MA mixtures are studied. Under the conditions of the experiments conducted in this work, combustion process was able to realize and at the same time the samples burned completely at a nickel content of 10 to 60 wt.% in the 5Ti + 3Si + xNi system. After MA, the samples from the 5Ti + 3Si mixture burned to the end, and during the activation of the 5Ti + 3Si + 40% Ni mixture, mechanochemical synthesis occurred. With increasing nickel content combustion temperature decreases, and combustion velocity behaves nonmonotonically, increases the size of composite particles and decreases the yield of the mixture after MA. MA practically did not affect the maximum combustion temperatures of mixtures of 5Ti + 3Si + xNi. A multiple (from 0.7 to 2.9 cm/s) increase in the burning rate of samples from MA mixtures with an increase in the Ni content from 20 to 30 wt. % was recorded. An increase in the nickel content leads to an increase in the content of triple phases and the amount of melt in the synthesis products of mixtures of 5Ti + 3Si + xNi. Shrinkage of product samples increases with increasing nickel content in the initial mixtures. After MA, the shrinkage of the product samples is replaced by their growth. Explanations of the observed dependencies are proposed.

The work is devoted to the study of the influence of the conditions for obtaining materials based on the synthetic polymer polylactide on their physico-mechanical and rheological characteristics. These materials are promising for the creation of biodegradable polymer implants of temporary action to maintain the mechanical properties of broken bones during the healing period. They are designed to replace the titanium fixators currently used for these purposes, which is due not only to the need for repeated surgery to extract them, but also to the fact that the strength and modulus of elasticity of titanium fixators exceed the values of bone strength indicators by an order of magnitude, which can cause the phenomenon of bone resorption and a decrease in its strength. It has been established that with an increase in temperature in the plasticization and pressing zone, as well as with an increase in pressure in the press, there is a natural decrease in the viscosity of the polylactide melt, as well as the values of the elastic modulus and breaking stress of solid samples. Varying the cooling rate of the material during the pressing process affects the degree of its crystallinity. At the same time, the lower the cooling rate, the greater the degree of crystallinity of the polylactide and the greater the values of the elastic modulus and breaking stress.

Composites of polyether polylactide (PLA) synthesized from natural raw materials with graphite nanoplates (GNP), which represent a new type of composite materials based on biodegradable polymers, were obtained by solid-phase method under the action of shear deformations. The porosity of composites was evaluated and their electrical and mechanical properties were studied. The effect of UV radiation on the molecular weight and molecular weight distribution of PLA in PLA-GNP composites of different compositions was investigated using the method of excision chromatography (EC), and the effect of the GNP nanofiller content on the change of their mechanical characteristics in the process of radiation was shown.

A modified version of using of the sol-gel process at the initial stage of the synthesis of a high-temperature superconductor (HTSC) Y_1-xFe_xBa₂Cu₃O_y with low Fe doping is proposed. The properties of samples obtained by sol-gel and solid-state synthesis have been compared. It has been shown that a more uniform distribution of the dopant throughout the volume of the sol-gel samples makes it possible to obtain materials with improved microstructural and performance characteristics.