A. N. Ozerin

Multiple cracking of rigid platinum film covering polymer substrate

Multiple cracking of a thin platinum film deposited on polyethylene terephtalate, isoprene rubber, and natural rubber substrates under tensile deformation was studied by light and scanning electron microscopy. The cover fractures on several fragments elongated in the direction perpendicular to the loading direction. The width of the fractured platinum fragments depends on the thickness of the deposited layer and applied tensile stress. A semiempirical equation describing the average width of the cover fragments was obtained. Appearance of a wavy pattern on an originally smooth surface of composites with rubberlike polymer substrate was observed. The mechanism of the appearance of the surface wave is a mechanical buckling instability of the cover under compressive force.

Hydrolysis of Titanium Alkoxides: Thermochemical, Electron Microscopy, Saxs Studies

Hydrolysis of Ti(OR)4 (R = Et, iPr, nBu) at various concentrations of titanium alkoxides and ratios h = [H2O] /[Ti(OR)4] is studied in alcoholic medium by means of calorimetry, electron microscopy, SAXS, and chemical analysis. The measured values for heat of hydrolysis of Ti(OR)4 by excess water (−Δ Hh) at 298.15 K comprise 14.2, 64.9, 19.3 kJ/mol for R = Et, R = Et, iPr, nBu respectively. −Δ Hh increases drastically in the region of 0<h<1 and demonstrates practically no changes with further increase of h ratio. In the solid hydrolysis product with the composition TiOx(OR)4−2x·y ROH, both x and y increase with increase of Ti(OR)4 concentration in solution. Bushy network first formed in solution as a result of hydrolysis gradually structures with formation of well-shaped spherical particles with diameters ≥0.2μm. SAXS curves analysis in the range of scattering vector values s = 0.07–4.26 nm−1 for Ti(OBu)4 hydrolysis products allows us to suggest their multilevel nature. Speculations on the structure of titanium oxobutoxide were made on the basis of the well-known structural data for crystalline first hydrolysis products of Ti(OEt)4 and Ti(Oi Pr)4. It is suggested to perform hydrolysis of Ti(OBu)4 with addition of water in two steps which allows us to decrease the rate of the solid precipitate formation, to regulate particles morphology in a wide range and to obtain well-shaped spherical species more than one micron in size. The influence of the powder size distribution on the grain growth during ceramic sintering is discussed.

The crystal structure of chitin and chitosan

Roentgenographic studies are performed to investigate the structural changes in chitin under pressure and shear during its solid-state processing using a twin-screw extruder and Bridgman anvils. The structure of chitosan synthesized by the solid-phase method is studied. Deformation under the conditions of dry extrusion grinding at room temperature reduces the crystallinity of the original chitin. Addition of water restores the crystallinity of the material up to the value characteristic of the original chitin. Extrusion processing of chitin at room temperature with addition of water virtually preserves the crystallinity and degree of ordering of the chitin crystal lattice, the same as ordinary dry grinding at an elevated (180°C) temperature. The maximum degree of amorphization of chitin is attained by its processing on Bridgman anvils. Solid-state synthesis of chitosan from chitin leads to a product with a more amorphous structure in comparison with chitosan produced by the suspension method.

X-ray Diffraction Study of the Structure of Detonation Nanodiamonds

The spatial structure of aggregates formed by detonation nanodiamonds is investigated using the wide-angle and small-angle X-ray scattering techniques. The effective sizes of crystallites and the crystallite size distribution function are determined. The shape of scattering aggregates is restored from the small-angle X-ray scattering data. An analysis of the results obtained allowed the conclusion that the nanodiamond aggregates have an extended spatial structure composed of nine to ten clusters, each involving four to five crystallites with a crystal lattice of the diamond type.

Complementarity of small-angle neutron and X-ray scattering methods for the quantitative structural and dynamical specification of dendritic macromolecules

The structural characteristics of polycarbosilane dendrimers with different molecular architecture were determined in solutions by small angle neutron and X-ray scattering. The same linear dimensions were sized up for the dendrimers both in benzene and chloroform. A solvent molecules penetration inside dendrimer structure in amount up to 30 vol.-% was found from the comparison of the partial and effective scattering volume for the dendrimers in solution.

The structure and properties of polymer composite fibers based on poly(vinyl alcohol) and nanodiamond of detonation synthesis

The structure and properties of the oriented poly(vinyl alcohol) fibers modified with nanodiamonds (NDs) and nanodiamond soot (NS) of detonation synthesis were investigated by wide-angle and small-angle X-ray scattering methods, as well as by electron microscopy and mechanical testing methods. It was shown that the introduced nanodiamond soot particles were dispersed within the polymer matrix while maintaining a high dispersion level without aggregation. The NS treated with ultrasound was found to be a more effective modifier of the mechanical properties of the oriented fibers than untreated soot and NDs. The maximum increase in the longitudinal elastic modulus over nonmodified fibers (from 30 GPa up to 45 GPa) and in the energy stored by oriented fiber modified with NS upon breaking (from 3 up to 6 J/g) was obtained at a small (1% by volume) soot content, which is technologically attractive. The values of the adhesive strength of the soot modified with ND (1%) with volume poly(vinyl alcohol) fibers in the epoxy matrix were measured, and the maximally achieved value (42 MPa) was higher than the adhesive strength of the nonmodified fibers and comparable with the value of the reference sample (steel wire (57 MPa)).

Properties of oriented film tapes prepared via solid-state processing of a nascent ultrahigh-molecular-weight polyethylene reactor powder synthesized with a postmetallocene catalyst

The correlation between the molecular mass of a nascent ultrahigh-molecular-weight polyethylene reactor powder synthesized with a postmetallocene catalyst and the specific features of plastic deformation during the orientational drawing of the material compacted and consolidated under laboratory conditions is studied. In the range 5 × 106−7 × 106, molecular mass is controlled via a change in the polymerization conditions. Under comparable conditions of orientational drawing, the highest values of strength (2.65 GPa) and the elastic modulus (100 GPa) are found for samples with M = 6.3 × 106.

Nanocomposites based on modified chitosan and titanium oxide

The effect of primary amino groups and molecular mass of chitosan on the stability of suspensions based on nanoscale TiO2 dispersions in acidic solutions of various concentrations at pH 2.5 was studied. In the case of chitosan prepared according to a commercialized process, the stability of TiO2 suspensions was low and depended on the concentration of the polymer solution. Solutions of low-molecular-mass highly deacetylated chitosan prepared by solid-phase synthesis stabilized a dispersion of nanosized TiO2 particles for a very long time. Nanocomposites based on a chitosan-PVA graft copolymer and TiO2 were prepared, in which the initial filler dispersion is retained up to very high filling ratios. A potential use of these nanocomposites in photocatalytic processes is discussed. The results of this study can be used for refining engineering procedures and processes for the manufacture of new biocompatible, bioactive, and biodegradable functional composite materials based on chitosan and synthetic polymers.

The spatial structure of dendritic macromolecules

A low-resolution ab initio shape determination was performed from small-angle neutron and X-ray scattering (SANS and SAXS) curves from solutions of polycarbosilane dendrimers with the three-functional and the four-functional branching centre of the fourth, fifth, sixth, seventh and eighth generations. In all cases, anisometric dendrimer shapes were obtained. The overall shapes of the dendrimers with the three- and four-functional branching centres were oblate ellipsoids of revolution and triaxial ellipsoids, respectively. The restored bead models revealed a pronounced heterogeneity within the dendrimer structure. The density deficit was observed in the central part and close to the periphery of the dendrimers. The fraction of the overall volume of the dendrimers available for solvent penetration was about 0.2-0.3. These results may help in the design of new practical applications of dendrimer macromolecules.

Self-diffusion and nuclear magnetic relaxation of dendritic macromolecules in solutions

The self-diffusion and nuclear magnetic relaxation of poly(butylcarbosilane) and poly(allylcarbosilane) dendrimers dissolved in deuterated chloroform and poly(amidoamine) dendrimers with hydroxyl surface groups in solutions with methanol have been studied. The diffusion rates(D) have been measured by the pulsed-field-gradient nuclear magnetic resonance. It is shown that experimental concentration dependencesD(ϕ) obtained for macromolecules in the dendrimer-solvent systems studied can be reduced to a unified view, and thus, the generalized concentration dependence of the normalized diffusion rates of dendrimers can be obtained. In the macromolecular volume concentration range from 0.01 up to 0.55, the generalized dependence of the normalized diffusion rates for dendrimers coincides with the analogous dependence for globular proteins in aqueous solutions; the last result suggests that self-diffusion features of dendrimers and globular proteins are in general similar. It is also shown that the experimental data obtained permit one to characterize the changes of the own monomer density of dendrimers depending on their molecular weight and, as a consequence, to make a conclusion about the swelling of dendritic macromolecules in the solutions studied.