A tungsten target has been exposed to pulsed laser ablation in vacuum, gaseous helium, and superfluid (liquid) helium, and ablation products have been studied by means of pyrometric measurements. It ...has been shown that quantitative measurement data for thermal emission characteristics shed light on nanostructure condensation mechanisms in these media. From these data, the cross sections of emitting particles have been calculated. It has been found that submicrometer particles emit mostly in vacuum, whereas emission from nanoparticles has been observed in superfluid helium. The obtained data are substantiated by electron microscopic data.
A comprehensive investigation of mineralogical and chemical composition as well as the technological properties of clay from the Krupeiskii Sad deposit of Belarus was conducted. The features of the ...formation of the structure and phase composition of heat-resistant ceramic materials obtained using polymineral clay raw materials in relation to the physicochemical properties and operational characteristics were established.
Creating biodegradable polymer compositions is an urgent problem. In this research, the processing parameters and physicomechanical properties of materials based on secondary polypropylene and ...secondary polyethylene filled with plant-based fillers are studied. It is estimated that the introduction of a filler leads to an increase in the maximal torsion torque; the lowest resistance against filler introduction is observed in the use of secondary polyethylene. Similar regularities are observed during the study of the minimal torsion torque; however, in this case, the lowest resistance is observed for the sample of secondary polypropylene. It is shown that the introduction of 10–15 parts by the mass of the filler leads to an increase in the elastic modulus and an insignificant decrease in the values of rupture stress and elongation upon breaking.
This article studies the structural and mechanical properties of polymer hydrogels based on polyelectrolyte complexes of N-succinyl-chitosan (NSC) with poly-N,N-diallyl-N,N-dimethylammonium chloride, ...depending on the composition of the reaction mixture and the conditions for obtaining complexes. The types of intermolecular interaction between the components of the complexes are studied by IR spectroscopy. The causes of swelling of coacervates based on polyelectrolyte complexes of N-succinylchitosan-chitosan with poly-N,N-diallyl-N,N-dimethylammonium chloride are analyzed. The relationship between the composition of coacervates and the structural-mechanical and transport properties of the gels formed from them is established. The developed approach to create elastic-viscous systems can be implemented when creating gel-like polymeric materials capable of self-organization into systems with controlled characteristics of the structure.
Manifestation of the supramolecular effect in reactions of the enzymatic hydrolysis of sodium carboxymethyl cellulose is studied. The occurrence of enzymatic hydrolysis under the action of ...nonspecific enzyme hyaluronidase is confirmed by the method of reducing sugars. The supramolecular structure of the polymer in solution is controlled using the approach including the use of cosolvents (modifiers), with a number of alcohols (ethanol, propylene glycol, and glycerol) being used as modifiers. It is shown that as polymer concentration in solution increases above 0.3 g/dL the rate of enzymatic hydrolysis almost ceases to raise with increasing concentration. This finding is associated with diffusion hindrances arising in interaction of the polymer with the enzyme due to an increase in the degree of aggregation of macromolecules in solution and formation of the entanglement network. In the presence of the modifiers in solution, the rate of enzymatic hydrolysis slows down. This effect can be explained by several factors: first, a decrease in the sizes of the macromolecular coil and an earlier formation of the entanglement network and, as a consequence, reduction in the accessibility of polymer units for interaction with the enzyme. Second, the modifying additives decrease the total β-glycosidase activity of hyaluronidase. It is demonstrated that the features of enzymatic hydrolysis in solution persist in the case of film samples.
This paper is devoted to studying the features of the release of medicinal substances (MSs, drugs) (both electrolyte and non-electrolyte) from solutions of polyelectrolytes through a semipermeable ...membrane. Polycation chitosan and polyanion sodium salt of chitosan succinyl are used as polymers, and cefazolin (CFZ) sodium salt, lidocaine hydrochloride (LH), and dioxidine (DO) are used as MSs. In the course of the study, the fact of the interaction between polyelectrolytes and drugs and the influence of the conformational and supramolecular state of polymers in a solution on the values of diffusion coefficients for the release of drugs from polymer solutions through a semipermeable membrane are established. It is shown that the interaction between drugs and polyelectrolytes has a number of characteristic features due to the ionogenic nature of the polymers used and the manifestation of the conformational-supramolecular effect. These features lead to the fact that a significant difference in the amount of the drug firmly retained by the polymer chain and the values of the diffusion coefficients of its release appear only in the region of dilute solutions. Upon transition to the region of semidilute solutions, due to changes in the structure of polymers in solution, these differences mitigated, which is accompanied by convergence of the diffusion coefficients for the release of various of kinds of drugs from polymer solutions through a semipermeable membrane.
The shock compressibility of single-crystal silicon is experimentally studied in the pressure range of 280 to 510 GPa. Shock waves are created using Mach’s explosive cumulative generators. The ...parameters of shock waves are determined by the impedance matching method, and single-crystal quartz is used as a ref-erence substance. The results agree well with the
ab initio
calculation results and with the data obtained using laser shock waves.
The interaction of macromolecules of the components of polymer complexes (PCs) based on poly-
N
-vinylpyrrolidone or polyethylene glycol with chitosan succinyl is studied by spectral and rheological ...methods. The presence of cooperative interaction between molecules through hydrogen bonds in the studied systems is proved by the spectroscopic method. It is shown that varying the molar ratio of polymers in the complexes changes the degree of the structuring of solutions based on them, which, in turn, affects the gel-forming and film-forming properties of the resulting systems. It is found that film materials based on individual polymers are characterized by low values of the contact angle of wetting. This indicates the high level of hydrophilicity of these materials, while films based on PCs have a lower surface hydrophilicity. Therefore, by modifying poly-(
N
-vinylpyrrolidone) or polyethylene glycol with chitosan succinyl, it is possible to impart greater lyophilicity to materials based on them, which will contribute to the multipoint interaction with them of active centers of biomacromolecules of the body.
Effect of a number of low-molecular-weight drug substances on the viscous and rheological behavior of pectin solutions in dilute and semidilute solutions regimes is studied. It is shown that the ...introduction of a drug substance, which is a low molecular weight electrolyte, into a dilute pectin solution leads to a change in the intrinsic viscosity of the polymer and the degree of aggregation of its macromolecules. Upon introduction of the drug substance into a semidilute pectin solution the rheological behavior of the solution changes. Presence of a drug substance of the nonelectrolyte nature in pectin solution has almost no effect on the conformational and supramolecular state of pectin and, accordingly, the viscosity characteristics of solution. It is demonstrated that the electrolyte drug substances, especially polyvalent cations, affect some practically important properties of liquid and soft dosage forms produced from pectin solutions, specifically the yield stress and the rate of drug substance release. The results obtained are explained by the polyelectrolyte nature of pectin.
The work is devoted to the study of thermal radiation accompanying the condensation of products of pulsed laser ablation of a tungsten target in vacuum, superfluid and gaseous helium. Pyrometric ...measurements have shown that the radiation characteristics depend on the medium. The obtained data imply that the sources of radiation in vacuum and gas are predominantly submicron particles, while in superfluid helium (He II) they are nanometer particles. These conclusions have been confirmed by electron microscopy data.
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