Valeriy Demchenko

DC field effect on the structuring and thermomechanical and electric properties of nanocomposites formed from pectin—Cu2+—polyethyleneimine ternary polyelectrolyte—metal complexes

With the use of combined structural methods, thermomechanical analysis, and dielectric spectroscopy, the effect of a dc field on the structuring and properties of ternary polyelectrolyte—metal complexes prepared from a stoichiometric polyelectrolyte complex based on the weak polyelectrolytes pectin and polyethyleneimine and CuSO4 salt, as well as nanocomposites formed from these complexes, has been studied. It has been found that the chemical reduction of Cu2+ cations in the bulk of a ternary complex under the action of a dc field occurs via the formation of a nanocomposite consisting of a polyelectrolyte complex and nanoparticles of only the metal Cu phase, whereas nanocomposite with Cu/Cu2O nanoparticles is formed in the absence of field. With the use of thermomechanical analysis and dielectric spectroscopy, it has been shown that, under a dc field, nanocomposites with higher structural glass-transition temperatures and electric conductivities are formed.

X-ray Study of Structural Formation and Thermomechanical Properties of Silver-Containing Polymer Nanocomposites

The structural organization and thermomechanical properties of nanocomposites prepared from interpolyelectrolyte–metal complex (IMC) involving anionic polyelectrolyte, pectin and AgNO3, and cationic polyelectrolyte, poly(4-vinylpyridine), have been investigated using the methods of wide- and small-angle X-ray scattering and thermomechanical analysis. It is established that chemical reduction of Ag+ ions in the IMC by sodium borohydride results in formation of the nanocomposite based on the “pectin–poly(4-vinylpyridine)” interpolyelectrolyte complex (IPEC) and Ag0 nanoparticles as well. At the same time, the level of nanocomposites’ structural heterogeneity is substantially enhancing, while effective size of the heterogeneity regions decreases. The nanocomposites IPEC–Ag0 prepared are shown much bigger Tg value and enhanced ability for deformation than those for IMC.

Nanostructurization and thermal properties of polyethylenes’ welds

As it is known, polyethylene (PE) is one of the common materials in the modern world, and PE products take the major share on industrial and trade markets. For example, various types of technical PE like PE-63, PE-80, and PE-100 have wide industrial applications, i.e., in construction, for pipeline systems etc. A rapid development of plastics industry outstrips detailed investigation of welding processes and welds’ formation mechanism, so they remain unexplored. There is still no final answer to the question how weld’s microstructure forms. Such conditions limit our way to the understanding of the problem and, respectively, prevent scientific approaches to the welding of more complicated (from chemical point of view) types of polymers than PE. Taking into account state-of-the-art, the article presents results of complex studies of PE weld, its structure, thermophysical and operational characteristics, analysis of these results, and basing on that some hypotheses of welded joint and weld structure formation. It is shown that welding of dissimilar types of polyethylene, like PE-80 and PE-100, leads to the formation of better-ordered crystallites, restructuring the crystalline phase, and amorphous areas with internal stresses in the welding zone.

Constant Electric and Magnetic Fields Effect on the Structuring and Thermomechanical and Thermophysical Properties of Nanocomposites Formed from Pectin–Cu 2+–Polyethyleneimine Interpolyelectrolyte–Metal Complexes

Applying wide-angle X-ray scattering method, thermomechanical analysis, and differential scanning calorimetry, the structural organization and properties of nanocomposites formed by chemical reduction of Сu2+ cations in the interpolyelectrolyte–metal complex (pectin–Cu2+–polyethyleneimine) under the influence of a constant magnetic and electric fields have been studied. It has been found that the chemical reduction of Cu2+ cations in the interpolyelectrolyte–metal complex bulk under constant electric and magnetic fields leads to formation of nanocomposite consisting of interpolyelectrolyte complex, including pectin–polyethyleneimine and nanoparticles of the metal Cu phase, whereas nanocomposite with Cu/Cu2O nanoparticles is formed in original state (without any field). It was observed that, under constant field, nanocomposites obtained have higher structural glass-transition temperatures and thermal stability.

β-Cyclodextrin-containing pseudorotaxanes as building blocks for cross-linked polymers

Rotaxanes and pseudorotaxanes are the supramolecular objects that attract much attention due to their low toxicity, sliding, dethreading and easy modification. Thus, polyrotaxanes and polypseudorotaxanes can be considered as components in drug delivery systems, sensor devices, implants, contrasting agents, fluorescent probes in other diagnostic systems. Therefore, we have prepared the pseudorotaxanes based on the β-cyclodextrin (β-CD) and molecule-“guest”—polyoxypropylenedimethacrylate (POPDMA) as carrier of end-capped methacrylate groups. The presence of such groups allows pseudorotaxane to be co-polymerized with acrylamide and methylene-bis-acrylamide and to develop cross-linked polymer matrices, which implies their further investigation as systems for a drug release. The structure of these substances was confirmed by FTIR- and NMR-spectroscopy, differential scanning calorimetry (DSC), X-ray analysis [wide-angle X-ray scattering (WAXS)], pyrolysis mass spectrometry. The ratio of POPDMA to β-CD was found to be 1:3, according to NMR data. The interactions between β-CD and POPDMA in the aqueous solution and in the dry mechanical mixture are entirely different, due to formation of pseudorotaxane. The results obtained by pyrolysis mass-spectrometry, WAXS and DSC well correlate with mechanism of formation of inclusion complexes, involving a linear molecule and cyclodextrins as described earlier.

Structural Peculiarities and Properties of Silver-Containing Polymer Nanocomposites

Structural, thermomechanical, and antimicrobial properties of nanocomposites based on interpolyelectrolyte complex and Ag nanoparticles, which are formed by the chemical and thermal reduction methods from interpolyelectrolyte–metal complexes (IMC), have been investigated. It is established that chemical reduction of Ag+ ions in the pectin–Ag+−poly(4-vinylpyridine) IMC, involving sodium borohydride at molar ratio [BH4−]:[Ag+] ≥ 1.0, results in formation of the nanocomposite based on the “pectin–poly(4-vinylpyridine)” interpolyelectrolyte complex (IPEC) and silver nanoparticles (Ag) as well. Applying small-angle X-ray method, we confirmed that at transformation from IMC to IPEC–Ag structure of nanocomposite, the relative heterogeneity level is augmented, while effective size of the region heterogeneity goes down. The nanocomposites pectin–poly(4-vinylpyridine)–Ag prepared are shown much higher Tg value and enhanced ability for deformation than those for IMC. Another type of nanocomposites on the base of interpolyelectrolyte complexes “pectin–polyethyleneimine (PEI)” and Ag nanoparticles was obtained by both chemical and thermal reduction of Ag+ ions in the polyelectrolyte–metal complexes. Such type of nanocomposites with Ag nanoparticles incorporated into polymer matrix is obtained due to the chemical reduction of Ag+ ions by NaBH4 in the interpolyelectrolyte complex, and appearance of the silver metallic phase is observed in full extent, while BH4−:Ag+ molar ratio is equal to 2.0. It is defined that thermal reduction of Ag+ ions in IMC bulk (while films are heated to the temperature around 100 °С and more) results in formation of silver-containing nanocomposites. In its turn, thermal reduction of silver ions is found out to take place owing to polyethyleneimine (namely, on account of electron transfer from the amino groups’ nitrogen atoms of polyethyleneimine to Ag+ ions). The antimicrobial investigation of the elaborated nanocomposites revealed they possess a high antimicrobial activity against S. aureus and E. coli strains.

Structure and Electrical/Dielectric Properties of Ion-Conductive Polymer Composites Based on Aliphatic Epoxy Resin and Lithium Perchlorate Salt

Nowadays, one of the most important research directions in development and creation of functional polymeric materials is a search of new solid electroactive polymers with high ionic conductivity at elevated temperatures. Particularly, the widening range of materials, which can be used for this purpose, is relevant. The present work is concerned with hybrid amorphous polymers synthesized basing on epoxy oligomer of diglycide aliphatic ester of polyethylene glycol (DEG-1) that was cured by polyethylene polyamine and lithium perchlorate salt. Structural peculiarities of the synthesized polymer composites were studied by differential scanning calorimetry, wide-angle X-ray spectra, infrared spectroscopic, scanning electron microscopy, elemental analysis, and transmission and reflective optical microscopy. The presence of ether oxygen in DEG-1 macromolecules provides a transfer mechanism of the lithium cations with the ether oxygen similar to polyethylene oxide. Thus, the obtained hybrid polymers have high values of ionic conductivity σ′ (approximately 10−3 S/cm) and permittivity e′ (6 × 105) at elevated temperatures (200°С). On the one hand, the results showed that the introduction of LiClO4 salt into epoxy polymer leads to formation of the coordinative metal-polymer complexes of donor-acceptor type between central Li+ ion and ligand. On the other hand, the appearance of amorphous microinclusions, probably of inorganic nature was also found.

Structure, Morphology, and Properties of Copper-Containing Polymer Nanocomposites

The morphology, structural organization, and thermomechanical and antimicrobial properties of nanocomposites prepared involving a natural and synthetic polymers – pectin, polyethyleneimine, and Cu/Cu2O or Cu nanoparticles – obtained by the chemical and thermal reduction of copper ions in the interpolyelectrolyte–metal complexes have been investigated. Such type of nanocomposites with Cu/Cu2O core–shell nanoparticles incorporated into polymer matrix is obtained due to the chemical reduction of Cu2+ ions by NaBH4 in the interpolyelectrolyte complex, and appearance of the copper’s metallic phase is observed in full extent while BH4−: Cu2+molar ratio being equal to 6.0. Applying thermomechanical analysis, it was observed that transformation of interpolyelectrolyte–metal complexes into nanocomposites results in decreasing of their glass-transition temperature. It is defined that Cu2+ ions thermal reduction in interpolyelectrolyte–metal complexes bulk (while films are heated to the optimal temperature around 170 °С) results in nanocomposites based on interpolyelectrolyte complexes “pectin–polyethyleneimine” and Cu nanoparticles being formed. It has been shown by thermomechanical analysis that the optimal time for complete thermal reduction of Cu2+ ions to metallic copper at T = 170 °С is 30 min. The antimicrobial investigations of the elaborated nanocomposites revealed they possess a high antimicrobial activity against S. aureus and E. coli strains.