Vol 12, No 1 (2018)

Thermogravimetry is used to study the thermodestruction of nitrocellulose (NC) with various nitrogen contents at various heating rates. At high degrees of nitration and high heating rates of the sample, the reaction occurs in an explosion mode with a threshold of its weight loss depending on the temperature. To explain this behavior, it is assumed that the nitration of cellulose gives rise to structural stresses, which weaken the covalent bonds in it by ∼37 kJ/mol (at a nitrogen content of ∼13%). This process apparently involves two different mechanisms of weight loss during heating: (a) conventional thermal destruction of NC macromolecules through the rupture of covalent bonds (with k₀ = 10¹³ s⁻¹, E = 150.2 kJ/mol, and n = 1) at heating rates of up to 10 K/min and nitrogen content in NC of up to 9%; (b) Zhurkov’s thermofluctuational mechanism of the destruction of strained macromolecules, characterized by a sharp (threshold) dependence of the weight loss on the heating rate, which is operative at heating rates above ∼4 K/min and high (>13%) nitrogen contents and at 20 K/min and a low (∼9%) nitrogen content. Under conditions of rapid heating, ∼10–20 K/min, the work done by stressed states to overcome the potential barrier to the rupture of covalent bonds causes an increase in the decomposition rate by a factor of 2000. The observed threshold pattern of weight loss during the thermodestruction of NC explains the long-known critical dependence of the properties of NC used to manufacture propellants on small changes in the nitrogen content.

The thermolysis of 2,4,6-triazido-1,3,5-triazine (I), 2,4,6-triazidopyrimidine (II), and 2,4,6-triazidopyridine (III) and its products were studied by DSC, mass spectrometry, IR spectroscopy, and electron microscopy. The thermal transformations of I gave planar nets formed by polyconjugated C–N bonds arranged into bundle aggregates. The thermolysis product of III consists of low-molecular compounds and has globular morphology. The thermolysis of II resulted in a mixture of products of both types, among which the planar nets were dominant. The relationship between the structure of the products of the thermal transformations of I, II, and III and the kinetic characteristics of these processes was discussed.

A relativistic multimode Jahn−Teller effect for tetrahedral molecular complexes in a triplet electronic state is considered. The analysis is based on the symmetry properties of the electronic Hamiltonian and its generalized symmetry operators, acting on both the coordinates (spatial operations) and spins (matrix operations) of the electrons. As a result, a 9 × 9 vibronic matrix that includes the vibronic coupling constants of orbital and spin-orbital nature and depends on the five normal modes of t₂ and e symmetry has been obtained.

The spectral-fluorescent properties of various supramolecular systems based on chlorin e₆ (Ce₆) are determined to facilitate the development of new medicines for photodynamic therapy and diagnostics. The effect of various excipients, such as poly-N-vinylpyrrolidone (PVP), polyethylene glycol (PEG), bovine serum albumin (BSA), chitosan, Triton X-100 (TX-100), sodium hexametaphosphate (SHMP), and poly(dimethyldiallylammonium chloride) chloride (PDDAC), on the optical absorption and fluorescence of Ce₆ is demonstrated. In the Ce₆−PVP, Ce₆−PEG, Ce₆−BSA, Ce₆−TX-100, Ce₆−SHMP, and Ce₆−PDDAC systems, Ce₆ molecules are disaggregated and complexes thereof with excipients are formed. The quantum yield of Ce₆ fluorescence in supramolecular systems is close to that of the free-form photosensitizer, in the absence of excipients. The results suggest that supramolecular complexes of Ce₆ are promising for the development of medicines with controllable photodynamic activity.

The strings formed in the solutions of trifluoroacetylated amino alcohols in cyclohexane were studied. It was found that microscopic strings with the diameter d ∼ 1 μm were woven from tightly coupled rigid submicroscopic strings with the diameter d ∼ 0.1 μm in increments of >100 μm. Therefore, the compound strings are transparent, and they usually look like an unstructured cylinder. Microscopic strings can be tightly combined in strings to 60 μm in diameter. Submicroscopic strings are arranged almost parallel to the axis of a microscopic string. The microscopic string acts as a polarizer: it transmits light polarized across its axis and absorbs light polarized along the axis. The majority of these properties can be explained based on the assumption that a connection between the strings of all hierarchical levels in cyclohexane is stronger than that in solvents with different string morphology.

Hydrodynamic instability is examined with consideration given to the viscosity of the fresh gas and combustion products, as well as to the dependences of the flame speed on the front curvature and of the transport coefficients on the temperature. For the perturbation frequency, an approximate second-order dispersion equation is derived. The flame is completely stable at very high viscosity or small dimensions. The greatest destabilizing role of the thermal expansion coefficient manifests itself at its relatively small values. As the expansion coefficient increases, the viscosity of the gas in the flame zone increases rapidly. In addition, the stabilizing effect according to the Markstein model is enhanced by thermal expansion.

The laser initiation of PETN is studied using the hydrodynamic approximation. The calculated and measured values of the threshold energy fluence for the laser initiation of PETN are compared.

The effect of a small Xe additive on the conditions of detonation initiation in incident shock waves of various intensities is studied. The experiments are carried out on a shock tube facility with 10% H₂ + 5% O₂ + 85% He, 10% H₂ + 5% O₂ + 84.75% He + 0.25% Xe, and 10% H₂ + 5% O₂ + 84.5% He + 0.5% Xe mixtures. The addition of Xe led to a shift in the detonation threshold toward weaker shock waves. This effect is probably due to a significant increase in the frequency of high-energy collisions between O₂ and Xe molecules in the shock wave front in comparison with that characteristic of the equilibrium behind the wave, a factor that significantly accelerates the chemical reaction between O₂ and H₂ behind the front. The effect is a consequence of the formation of a specific translational nonequilibrium in the wave front. A previously performed numerical study of the distributions of pairs of O₂ and Xe molecules in the shock wave front shows that this effect can be enhanced by decreasing the Xe concentration from 0.5 to 0.25%. The experiment performed indirectly confirms this conclusion. It turns out that, for the mixture with 0.25% Xe, the detonation threshold shifts more strongly to the region of weaker shock waves than for the mixture with 0.5% Xe. This result gives additional arguments in favor of the assumption that this effect is due to the specifics of the translational nonequilibrium in the wave front.

Experiments on the measurement of air emission intensity behind the front of incident shock wave were carried out in a shock tube at an initial pressure of 0.25 Torr and shock wave velocities of 6.3–8.4 km/s. The emission intensity was measured in absolute units both in the form of an integral spectral distribution in a wavelength range of 120−400 nm (panoramic spectra) and as the time evolution of emission at the individual atomic lines of nitrogen and oxygen atoms. The results of the measurements demonstrated that the emission in air behind a shock wave in the vacuum ultraviolet region of 120–200 nm had a much higher radiation flux level than the emission in a range of 200–900 nm.

Under dynamic loading, the interaction of unloading waves with each other and with the faces causes the deformation of the sample due to the formation of standing waves, at the nodes of which the localized- deformation bands arise (if the high-speed tension does not exceed the spall strength, so the material in the zone of interference of unloading waves preserves its continuity). A consequence of deformation localization is the mass transfer of atoms and the doping phase particles to nascent localized-deformation bands. The duration of stress oscillations in standing waves in the ultrasonic frequency range exceeds the duration of the initial impulse by at least two orders of magnitude, which ensures an increase in the distance traveled by atoms and dispersed particles during deformation in standing waves.

The effect of Co₃O₄ and ZrO₂ additives on the sensory response of In₂O₃-based nanostructured composites to H₂ and CO is studied. It is shown that the addition of small amounts of Co₃O₄ or ZrO₂ to In₂O₃ leads to a sharp increase in the sensory response to hydrogen. The maximum sensory response of the ZrO₂−In₂O₃ composite to 1100 ppm of hydrogen increases from 80 to 270 as the ZrO₂ content changes 0 to 20 wt %. The response to CO varies only slightly. For Co₃O₄−In₂O₃ composites, the maximum response to H₂ and CO increases with the Co₃O₄ content within 0−10 wt %. A further increase in the Co₃O₄ content leads to a significant decrease in the response, with composites containing ∼60 wt % Co₃O₄ being characterized by a very low efficiency. In the Co₃O₄−In₂O₃ system with a content of up to 60 wt % Co₃O₄, electronic conduction is realized, which changes to hole conduction at Co₃O₄ within 80−100 wt %. In the ZrO₂−In₂O₃ system, electric current flows through In₂O₃ nanocrystals, i.e., n-type conduction takes place. Possible reasons for the observed effects are discussed.

The reactions of the polysaccharides pectin (Pc) and chitosan (CTS) with antibiotics of cephalosporin and aminoglycoside series were studied. The complexation between the drugs and polymers was found to occur via hydrogen bonding. Dilution of the chitosan polycation increased the probability of occurrence of the negative ions of the cephalosporin antibiotic near the chain and lowered the probability of occurrence of the positive ions of aminoglycoside antibiotics, which affected the amount of adducts. When the pectin polyanion was diluted, the opposite situation was observed.

The effect of small additions of the iron(III) complex with tetraphenylporphyrin (0–5%) on the structure and properties of ultrathin fibers based on poly(3-hydroxybutyrate) (PHB) was studied by differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD), EPR probe method, and scanning electron microscopy. When tetramethylporphyrin was added to the PHB fibers, the crystallinity significantly increased, and the molecular mobility in the amorphous regions of the polymer decreased. The thermal treatment of the fibers (annealing at 140°C) led to significantly increased crystallinity and decreased molecular mobility in the amorphous regions of the PHB fibers. The addition of tetramethylporphyrin to the PHB fibers led to a sharp decrease in crystallinity. Ozonolysis of the fibers at small treatment times caused a considerable decrease in their molecular mobility (to 5 h), while prolonged ozonolysis led to increased mobility. The obtained fibrous materials have bactericidal properties and will find use in the development of antibacterial and antitumor therapeutic systems.

The structural, electronic, and magnetic properties of iron oxide nanoparticles encapsulated in hybrid biodegradable therapeutic systems based on poly-3-hydroxybutyrate and chitosan are comprehensively studied using Mössbauer spectroscopy, X-ray diffraction, small-angle X-ray scattering, and macroscopic magnetization measurements. It is shown that iron oxide in concentrations of 4 and 8 wt % in the polymer matrix of magnetically isotropic and magnetoanisotropic systems exists in the form of nanosized (d ≈ 7–8 nm) superparamagnetic clusters. Iron oxide clusters have the structure of a nonstoichiometric inverse spinel, intermediate between polymorphous modifications of Fe₃O₄ and γ-Fe₂O₃.

Nanocrystalline composite materials based on magnetite Fe₃O₄ and humic acids (HA) were synthesized and characterized. Investigation of these materials by EPR, fluorescence spectroscopy, electron microscopy, and XRD analysis showed that the surface of magnetite nanoparticles was densely covered with HA molecules, the size of the Fe₃O₄ nucleus decreasing when the HA : Fe₃O₄ ratio increased. An EPR study showed that the structure of the ferromagnetic magnetite nanoparticles changed at increased HA contents. The IR and fluorescence spectroscopy data suggest active participation of carboxyl and hydroxyl groups of HA in the adsorption of HAs on the Fe₃O₄ surface. The main types of interaction of Fe₃O₄ with HA were considered, and a scheme of possible chemical reactions was proposed.

Plasma-chemical processes in air are studied. Based on numerical simulations, the background concentrations of the main charged species are determined under normal conditions and at increased rates of formation of fast particle due to seismic activity. An analysis of the composition of air plasma is carried out at various humidities.