Dicarboxylic acids amides as an acceptor of formaldehyde in urea-formaldehyde resins

The possibility of reducing the content of free formaldehyde in urea-formaldehyde resin by introducing into the final resin composition of diphthalic and dimaleic acids amides was studied. It was found that the amides synthesized are able to participate in formaldehyde addition as well as in its polymerization and they are effective acceptor of formaldehyde in urea-formaldehyde resins.     

AFM investigation of films based on UV-solidified powder oligoesterdimethacrylate compositions

The morphology, supramolecular structure, and thermal behavior of powder coatings based on UV-solidified oligoesterdimethacrylate powder compositions with and without reactive coreactant bis-styrenated urethane prepared on different substrates have been studied using atomic-force microscopy, X-ray phase analysis, and differential scanning calorimetry. It was found that addition of the reactive coreactant in powder compositions results in homogenization of structure and morphology of coatings and increase in their glass transition temperatures by more than 10 K. The character of their morphology depends also on the conditions of film formation and substrate material. Unmodified coatings formed on a steel substrate exhibit an anisotropic structure, in contrast to the coatings prepared on the PTFE substrate, which are isotropic and represent a homogeneous polymer matrix containing aggregates formed by inclusions of nanoand microdimensions.     

Structure and phase composition of BiFeO3 : La films synthesized by chemical deposition from solutions

The transmission electron microscopy, energy-dispersive, and X-ray powder diffraction analyses have been used to study the changes in the structure and phase composition of lanthanum-doped BiFeO₃ and undoped BiFeO₃ thin films synthesized by chemical deposition from solutions and annealed in the temperature range 500?C700°C. It has been found that the temperature of the onset of crystallization with formation of the rhombohedral phase of BiFeO₃ is 500°C. As the annealing temperature increases, the phase composition of the film is changed: the Bi_3.43Fe_0.57O₆ and Bi₂Fe₄O₉ phases are formed. The lanthanum doping increases the crystallization temperature to 550°C; in this case, the film remains single-phase to T = 700°C.     

Microobject manipulations using laser beams with nonzero orbital angular momentum

Microobject manipulation with a laser is investigated. The functional capabilities of the laser manipulators can be significantly enhanced using beams with predetermined distributions of intensity and angular momentum. Beams with nonzero angular momentum are generated using phase and amplitude-phase masks. Such beams make it possible to rotate weakly absorbing particles and to move them along a given trajectory. Experimental results on the microobject motion along various trajectories (circle, triangle contour, self-intersecting curve, and Archimedes spiral) are presented.     

Development of the model of HF radiowave propagation in the ionosphere

The model of HF radiowave propagation, based on a geometrical optics approximation, has been extended for the case of a complex geometrical optics. The radiowave propagation in the illuminated region without going to the caustic shadow region is considered. The radiowave propagation model has been generalized for the case of wideband HF signals in the ionosphere. A dynamic representation of LFM signals in the form of a wave packet sequence was used for this purpose. The radiowave propagation model was also adapted to a global self-consistent dynamic model of the thermosphere, ionosphere, and protonosphere, which made it possible to study specific features in the formation of HF radiowave ray paths during geomagnetic storms in a 3D inhomogeneous anisotropic medium.     

Influence of temperature on the adsorption of α-tocopherol from ethanol solutions on acid-activated clinoptilolite tuff

Patterns in the adsorption of α-tocopherol on acid-activated clinoptilolite tuff at 283, 295, 305, and 333 K are established and explained. It is found that the selectivity of the sorbent toward the vitamin rises as the temperature of the process falls. The adsorption of α-tocopherol from dilute solutions is described in terms of the Langmuir adsorption theory. It is shown that the fixing of vitamin E monolayers in the structural matrix of clinoptilolite tuff is due to the formation of hydrogen bonds between isolated silanol groups of the adsorbent and oxygen atoms of the chromane ring and the phenol residue of α-tocopherol. The thermodynamic functions of monolayer adsorption of the vitamin are estimated. It is concluded that the formation of polymolecular layers in the form of associates is due to hydrophobic interactions between side substituents of α-tocopherol.     

Photocatalytic activity of water-soluble tetrapyrrole compounds in the presence of amino-containing polymers

It was demonstrated that the activity of tetrapyrrole photosensitizers (TPSs) of singlet oxygen generation (dimegin, tetrasulfophenylporphyrin, and photoditasine) in the oxidation of tryptophan in the aqueous phase decreases in the presence of polymers containing free amino groups (chitosan and polyallylamine). The decrease of the activity is accompanied by the change of the electronic absorption spectra of the TPSs. Analogues of chitosan with screened amino groups (chitosan sulfate and carboxymethylchitin) or without amino groups (carboxymethylcellulose), as well as hexamethylenediamine, a low-molecular-weight compound, do not affect the activity of the TPSs. The regularities observed can be accounted for by the association of molecules of the tetrapyrroles initiated by the complexation of the TPSs having external salt groupings with free amino groups of the polymers.     

Adhesive prepregs and composite materials on their basis

The properties of high-strength and high-elasticity film-forming adhesives, high-strength cold- and hot-setting adhesive pastes, functional adhesives for metals, and various nonmetal and composite materials are reviewed. The properties of self-adhesive materials of different grades used for temporary repair of airframe surfaces are also described.     

Vibrational spectra of lanthanide endofullerenes with different symmetries of molecular structure

Quantum-chemical calculations of the geometric structure and vibrational spectra of lanthanide endofullerenes have been carried out. The vibrational frequencies of lanthanide atoms depend substantially on the symmetry of the molecular structure of the endofullerene and on the distance between the metal atom and the carbon cage. The infrared spectra of the endofullerenes M@C₆₀ contain vibrations that are forbidden by symmetry for the empty fullerene C₆₀. A change in the vibrational spectra due to the encapsulation of a metal atom in fullerenes with a C₆₀ cage is considerably more pronounced than that of the higher fullerenes. In the vibrational spectra, there are lines not characteristic of C₆₀, which indicates the presence of M@C₆₀ endofullerenes in a mixture with C₆₀ fullerenes.