Self-assembly of ionogenic surfactants during their interaction with poly(propylenimine) dendrimers

The structure of complexes formed by poly(propylenimine) dendrimers of five generations and anionic micelle-forming surfactants is studied by X-ray diffraction. It is shown that, in complexes of lower generation dendrimers, the lamellar packing of surfactants is dominant. In complexes formed by dendrimers of the fourth and fifth generations, packing typical of compact dendrimer molecules prevails. This packing can be attributed to the distorted dense packing of ball-like complex species. Structural models of complexes that allow for penetration of surfactants into the dendrimer molecule and the size ratio of the aliphatic radical of a surfactant and a dendrimer are advanced.     

The effective characteristics and electroelastic state of active composite elements

For rods in which the piezoelectric and elastic layers are perpendicular to the rod axis and the lamination has a periodic structure, formulae for the effective characteristics of inhomogeneous material are obtained and the equations that describe the electroelastic state are constructed by the asymptotic method of homogenization. Such active composite elements are known as stacks. As an example, the electroelastic state of stacks executing forced harmonic vibrations under the action of an electrical load is calculated, the effective characteristics of material are found, and both the slowly varying state described by the rod theory and the rapidly varying state caused by the inhomogeneity of the layered structure are calculated. The effect of the thickness of weak adhesive layers on the electromechanical coupling coefficient, characterizing the stacks as energy convertors, is investigated.     

Absorption of ionic amphiphils by oppositely charged polyelectrolyte gels

Slightly cross-linked polyelectrolytes absorb oppositely charged surfactants in aqueous media. Transfer of amphiphilic ions from solution into the swollen network proceeds as a frontal heterogeneous cooperative reaction causing a collapse of the original polyelectrolyte gel. Small and wide angle X-ray diffraction data show that electrostatic complex formed as a result of the reaction consists of lamellar type surfactant micelles embedded in a polyelectrolyte network. It is also shown that such complexes contain equimolar amount of surfactant ions and ionized polyelectrolyte units paired with amphiphil head groups. In other words a charged network is not able to bind surplus oppositely charged surfactant ions. However, it is still able to solubilize a substantial amount of a nonionized surfactant. Chemical structure of surfactants strongly affect internal structure of lamellae and stability of the complexes.     

Comparative study of Cu(II) catalytic sites immobilized onto different polymeric supports

The catalysts with copper(II) ions stabilized onto different polymeric matrixes are prepared on either bulk (Cu/chitosan, Cu/polyethyleneimine-polyacrylic acid (PPA), and Cu-diiminate-impregnated polystyrene, polyarylate, or polymethylmethacrylate) or composite supports (egg-shell type Cu/chitosan/SiO₂ and Cu/PPA/SiO₂). The morphology of the samples and peculiarities of Cu(II) cationic sites are studied by SEM and ESR methods, and the catalyst activities are compared in oxidation of o- and p-dihydroxybenzenes by air in water. The catalytic activity of Cu(II) centers is governed by the coordination of isolated copper ions: for the most active catalysts, i.e., Cu/chitosan and Cu/PPA, the symmetry of isolated Cu²⁺-sites approximates a coordinatively unsaturated square-planar structure. At the same time, accessibility of active sites to water differs for different polymers, so the contribution of hydrophilicity to the reaction pattern cannot be excluded. Redox transformations of the active sites in the course of catalytic tests do not cause copper leaching from the polymer matrix. The binary composite systems with a film of low-loaded hydrofilic Cu-polymer supported on macroporous SiO₂ demonstrate substantially higher activity in oxidation of hydroquinone and 3,4-dihydroxyphenylalanine, as compared with the bulk Cu/polymer samples. In turn, the specific activity of Cu/chitosan/SiO₂ exceeds significantly that of Cu/PPA/SiO₂ due to stabilization of a thinner and more uniform film of chitosan at the surface of silica.     

Formation and transformations of polyelectrolyte gel-ampholyte dendrimer-surfactant ternary complexes

The reactions of complex gels formed via the sorption of a poly(propylenimine) ampholyte dendrimer of the fourth generation by oppositely charged lightly cross-linked polyelectrolyte hydrogels with ionogenic micelle-forming surfactants have been studied. The sorption of surfactant ions likely charged relative to the complexed ampholyte dendrimer by complex gels is associated with two parallel chemical reactions controlled by the concentration of the surfactant and pH which give rise to the formation of network-dendrimer-surfactant tertiary complexes. The reactions of complex gels with surfactant ions likely charged relative to the network polyelectrolyte make it possible at different solution pHs to prepare both negatively and positively charged hydrogels reinforced by disperse particles of the dendrimer-surfactant complex.     

Isotherms of thermal conductivity in PbTe-MnTe solid solutions

The temperature dependences of the thermal conductivity λ of PbTe-MnTe solid solutions (0–4 mol % MnTe) are measured in the range 170–670 K. The data obtained are used in constructing the isotherms of the lattice thermal conductivity λ_l and in estimating the effective cross section for phonon scattering by Mn impurity atoms. It is found that all the isotherms exhibit an anomalous increase in λ_l in the concentration range 1.25–2.0 mol % MnTe, which disagrees with the usually observed decrease in λ_l with an increase in the impurity concentration. It is assumed that the anomalous increase in λ_l manifests itself after attainment of the percolation threshold when a continuous chain of overlapping deformation fields produced by individual atoms (an infinite cluster) is formed in the crystal. In the crystal lattice, stresses are partly compensated and phonon scattering decreases. The assumption is made that the effect observed has a universal character.     

On the effect of ordering on vibrational spectrum of relaxor ferroelectric PbSc1/2Ta1/2O3 in paraphase

The effect of the ordering of Sc³⁺ and Ta⁵⁺ ions on the behavior of the phonon subsystem in the relaxor ferroelectric PbSc_1/2Ta_1/2O₃ from the numerous AB′ _x B″ _x?1O₃ family has been studied. The nature of an additional contribution to the light-scattering spectra has been analyzed on the experimental data on Raman scattering in PbSc_1/2Ta_1/2O₃, SrAl_1/2Ta_1/2O₃, SrAl_1/2Nb_1/2O₃, and BaMg_1/3Ta_2/3O₃ compounds and inelastic neutron scattering in PbSc_1/2Ta_1/2O₃. It is shown that broadening of the lines in the Raman spectra of PbSc_1/2Ta_1/2O₃ crystals is caused by additional scattering by phonons from various points of the Brillouin zone.     

1H Nuclear Magnetic Relaxation Spectroscopy of Ultradispersed Diamond Hydrosols

The spin-lattice relaxation of water protons in hydrosols of ultradispersed diamonds with the volume content of the dispersed phase up to 1% is studied by the high-resolution NMR. The relaxation rate of water protons is measured as a function of the dispersed phase concentration. It is shown that hydrosols of ultradispersed diamonds can be used as model systems for studying the relaxation parameters of aqueous phases in heterogeneous media.     

Self-oscillating reaction in the furan series

It was found for the first time that the acid hydrolysis of 2,5-dimethylfuran in water–ethanol solutions has self-oscillating character. Oscillations in the concentrations of the two products 2,5-hexanedione and an unidentified compound X were detected by GLC. The ranges of hydrochloric acid and ethanol concentrations in which these oscillations appear were determined. It is suggested that the formation of compound X results from tautomeric transformations of 2,5-hexanedione under the reaction conditions. Quantum-chemical calculations showed that the possible tautomers are formed with equal probability.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1619–1625, November, 2004.