Vol 10, No 5 (2016)

IR spectroscopy is applied to studying the effect of nonpolar and low-polar solvents on the molecular structure of solid-state quasi-one-dimensional strings formed through the chiral self-assembly from solutions of trifluoroacetylated homochiral amino alcohols (TFAAA). It is experimentally confirmed that in stable two-phase string/solvent gels and respective xerogels, solid-phase strings contain no solvent molecules as a structural element, experiencing, however, a weak disturbing influence of solvent molecules. It is shown that the process of spontaneous self-assembly of chiral strings in solutions is accompanied by the formation of a complex system of hydrogen bonds involving the C=O, N–H, and O–H functional groups of dissolved TFAAA molecules and by the displacement of solvent molecules to the periphery of the resulting quasi-one-dimensional strings. The results of the present work, together with data obtained by other experimental methods, indicate that TFAAA-based elementary strings have diameters of 1–2 nm, being crystalline, molecularly thin, quasi-one-dimensional objects. The amplitude of the thermally activated bending vibrations (transverse phonons) of elementary strings is sufficient to cause the entanglement of elementary strings, which leads to the formation of larger diameter supercoiled strings.

The selective catalytic reduction (SCR) of nitrogen dioxide in an air flow modeling the exhaust gas from an internal combustion engine is studied. Granulated V₂O₅ (13.5%)–MnO₂ (0.7–1.0%)/Al₂O₃ powder (AVK-10M catalyst) and ammonia injected into a SCR catalytic cell are used as a heterogeneous catalyst of NO₂ reduction and a reducing agent, respectively. If the efficiency of NO₂ removal is high enough and satisfies the requirements of the State Sanitary Standards for the maximum permissible concentrations of substances emitted into the atmosphere (\(MP{C_{N{O_2}}}\) = 0.085 mg/m³), the reducing agent (ammonia) is not completely consumed during SCR, so a considerable amount of NH₃ can be released into the atmosphere. Therefore, a strict control of both NO₂ and unreacted ammonia emissions is needed. The dependences of the concentrations of [NH₃] and [NO₂] on the [NH₃]/[NO₂] ratio for the model air flow passed through the AVK-10M granular heterogeneous catalyst are measured. It is found that the maximum degree of removal of NO₂ from the air takes place at [NH₃]/[NO₂] = 1.3. In the conventional process, the concentration of [NO₂] drop from 530.00 to 0.07 mg/m³, i.e., below the \(MP{C_{N{O_2}}}\) . At the same time, the ammonia concentration increases to [NH₃] = 3.4 mg/m³, which becomes 85 times the \(MP{C_{N{O_2}}}\) , 0.04 mg/m³. To remove unreacted ammonia from air flows, we developed [P–(SO₃^-)₂ · Me²⁺] sulfocationites, where Me are the Cu and/or Ca ions, P is a styrene–divinylbenzene copolymer. It is shown that the concentration of ammonia passed through the adsorption cell filled with a freshly sulfocationite drops below \(MP{C_{N{H_3}}}\) = 0.04 mg/m³. The dependences of the dynamic exchange capacity (DEC) before ammonia breakthrough for the [P–(SO₃^-)₂ · Cu²⁺] delta-sulfocationite on the air flow rate, [NH₃] concentration, and humidity are measured. The maximum value of the DEC, δ = 59.5 mg/cm³, is observed at an air flow velocity of 2.171 m/s, [NH₃] = 0.0035 mg/L, and 75% humidity. To illustrate practical applications of the proposed improved SCR method, it is shown that a 3-L replaceable [P–(SO₃^-)₂ · Cu²⁺] sorbent cartridge in a SCR exhaust gas purifier for a car internal combustion engine does not need replacement more frequently than every 50000 km.

A new method is suggested for solving the inverse problem of chemical kinetics. This method provides means to derive, from unsteady-state experimental data, the rate constants of catalytic reactions in which each step involves at least one main reactant. Examples of applying this method to two- and three-step reactions are presented.

Investigation of the kinetics of oxygen absorption by the aniline–styrene epoxide-p-toluenesulfonic acid ternary system (TS) in an acetonitrile solution led to a simple equation for the oxidation rate: V_TS = k[aniline]⁰ • [epoxide]⁰[acid]¹ at [aniline], [epoxide] ≫ [acid], k = 0.77 × 10^–3s^–1, and 343 K. The data obtained indicated that a complex of the three starting reagents formed before oxidation. In a mixed solvent containing tert-butanol, the dependence of V_TS on its composition was extremum. A scheme was suggested that explained the change in the dependence V_TS = k′[aniline]^–0.63[epoxide]^0.86[acid]¹ in the mixed solvent by the decomposition of the complex in the presence of alcohol.

Experimental results on the ignition of energetic two- and three-layer potassium picrate- and lead(II, IV) oxide-based compositions with a high-current electron beam of nanosecond duration are reported. It is shown that the sustainability of explosive transformations in layered compositions depends on the boundary conditions and the additional impact of the cathode flame (high-temperature metal plasma).

The ignition delay times for mixtures of isopropyl nitrate (IPN) with air and argon are measured in a rapid-injection reactor at a pressure of 1 atm and in a shock tube at 2–3 atm. It is shown that the ignition delay time τ of mixtures in which heat is largely released due to oxidation by the oxygen contained in the IPN molecule is determined by the unimolecular decomposition of IPN over the entire temperature range covered (500–730 K). For mixtures in which heat is mainly produced by oxidation reactions involving air oxygen, the ignition delay time at high temperatures is controlled by secondary reactions of oxidation of the hydrocarbon moiety of the IPN molecule, leading to an increase in τ by more than an order of magnitude. Liquid IPN burns in a nitrogen atmosphere only at pressures above 40 atm, at a linear rate of ~4 mm/s. The measured flame temperatures are in close agreement with the respective values calculated using a thermodynamic code.

The effect of lateral heat loss on the characteristics of the filtration combustion of solid organic fuels is studied experimentally and theoretically. The results show that, for an reaction trailing, an increase in the heat loss intensity leads to a marked reduction in the combustion temperature and an increase in the temperature at which fuel pyrolysis is complete, with the yield of liquid pyrolysis products remaining practically unchanged. For a reaction leading, an increase in the heat transfer coefficient causes a reduction in the combustion temperature and the yield of liquid pyrolysis products.

This study has been focused on the construction of a detailed kinetic mechanism of oxidation and combustion of isooctane (2,2,4-trimethylpentane) to describe both high-temperature reactions and the low-temperature multistage process with separated stages of “cool” and “blue” flames and hot explosion. In accordance with the proposed mechanism, isobaric autoignition, compression-induced autoignition, and flame propagation characteristics have been calculated; the calculation results have been compared with the experimental data. Satisfactory qualitative and quantitative agreement of the calculation and experimental results has been obtained.

Electrical and photoelectrical properties of nanocrystalline zinc oxide and indium oxide films are studied. For these oxides the temperature dependences of conductance are observed to be consisting of two parts with different activation energy. Also photoconductivity relaxation of the oxides can be described by a sum of two exponential functions. The spectral dependencies of nanocrystalline zinc oxide and indium oxide photoconductivity are presented. The photoconductivity arises as samples are illuminated with energy less than band gap. The data are discussed on the basis of model by which the localized states in the band gap play major role.

Nucleolus-like bodies (NLBs) of mammalian oocytes are a convenient object for studying the effects of laser radiation on cellular organelles during laser surgery operations. NLBs in mouse germinal vesicle oocytes (GV oocytes) were subject to nanosurgery by means of tightly focused femtosecond laser pulses at near-infrared wavelength. The damage threshold of the NLB material was one-half orders of magnitude below the threshold for the water breakdown by femtosecond pulses. An incision of NLB material with submicron resolution was obtained at a threshold pulse energy. At the pulse energy one order of magnitude higher than the threshold level, significant deformation and rupture of NLBs were observed. Anisotropic deformations of the NLBs and the dynamics of their relaxation indicate the presence of granular structure in these organelles. Mechanical strain and the formation of cavitation and steam-gas bubbles in the place of impact of laser pulses can be described with the help of a model of the laser breakdown of medium.

The ability of polytetrafluoroethylene (Teflon) films stretched in liquid styrene, toluene, and other organic liquids at room temperature to absorb these liquids is studied. It is found that, when stretched to 200% in air and liquids, the volume of the polytetrafluoroethylene (PTFE) film increases by 40%, whereas the amount of liquid sorbed reaches 34 vol %. Stretched PTFE–polystyrene nanocomposites were prepared by in situ thermal polymerization of styrene sorbed into a PTFE film during stretching in a styrene–toluene–initiator solution.

The effect of viscosity and electric conductivity of the polymer solution of poly-3-hydrobutyrate (PHB) on the formation of ultrafine fibers was studied. It was found that these parameters largely determine the geometrical parameters and morphology of the ultrafine fibers of PHB obtained by electrostatic forming. The increase in the viscosity of solutions at increased concentration and/or molecular mass of the polymer leads to an increase in the thickness uniformity of fibers and affects the diameter and diameter distribution width of the ultrathin fibers. Modification of the solutions with an ionogen electrolyte and hydrolytic agent (formic acid) decreases the initial molecular mass of the polymer and leads to increased viscosity of the system. The obtained fibers have found use in biomedicine, in particular, in the design of the elements of the locomotor system.

The molecular mobility of nanocellulose hydrogels isolated from microcrystalline cellulose is evaluated using the spin probe method, from the correlation time τ (s) and rotational frequency ν = 1/τ(s^–1) of stable nitroxyl radicals introduced into the medium under study. In an aqueous gel medium, the EPR spectrum of the probe features an anisotropic triplet of frozen particles over a temperature range of 77 to 265 K. In an aqueous–ethanolic gel solution, the temperature of onset of rotation of the radical is 85 K lower. The rotational correlation time is determined from the parameters of the EPR spectrum recorded in the temperature range of 180–290 K. The resulting Arrhenius temperature dependence logν = f(1/T) is used to evaluate the activation energy of rotation E of the radical and the preexponential factor ν₀(s^–1), the frequency of rotational vibrations of the particle around the equilibrium position. For the aqueous medium, E = 11.2 kcal/mol; in the presence of ethanol, E = 5.2 kcal/mol; the preexponential factors for the aqueous and aqueous–ethanolic media are ν₀ = 7 × 10¹⁸ and 6 × 10¹⁴ s^–1, respectively. The parameters E and ν₀ measured in the pure solvents and in the samples containing nanocellulose differ little, which is indicative of a high hydrophobicity of the probe molecule (and hydrogel particles) and of their weak interaction with the environment. The high value (~10¹⁸ s^–1) of the preexponential factor is explained in terms of the compensation effect of water.

The transport characteristics of bilayer graphene nanoribbons with hydrogen adatoms in an external static electric field is studied. The adsorption of hydrogen atoms on the surface of bilayer graphene ribbons is considered within the single-impurity periodic Anderson model. The transport coefficients of impurity-doped bilayer graphene ribbons are simulated in the relaxation time approximation. At a constant concentration of hydrogen adatoms, a nonlinear dependence of the transport coefficients on the static electric field strength has been revealed. It is found that the electrical conductivity and the diffusion coefficient of electrons in bilayer graphene ribbons decrease with increasing concentration of hydrogen adatoms.

A similarity between the diffusion equation and the Schrödinger equation is used to treat the problem of gas–surface reactions, with consideration given to the coupled processes of adsorption, surface chemical conversion, energy relaxation into the bulk, and surface diffusion over a regular one-dimensional chain of active surface sites. It is found that, in accordance with qualitative physical considerations, the nonequilibrium surface diffusion of the reaction precursor results, with an appreciable probability, in the formation of products not only at the initially attacked surface site, but also at neighboring sites.

The algorithm and the results of calculations of the dynamics of stratospheric ozone depletion at mid-latitudes are reported. The data were obtained based on numerical simulations of the dynamics of gas-phase and heterophase reactions involving Junge layer particles. The contribution of heterophase reactions to the ozone layer depletion is evaluated, and the necessity of considering them in predicting the recovery of the ozone layer in the XXI century is justified.