Modification of Polyvinyltrimethylsilane in Direct-Current Discharge

High Energy Chemistry - The modification of polyvinyltrimethylsilane under treatment by direct-current discharge at a reduced pressure has been investigated. Polymer films were placed at the anode...     

Displacement of a viscous fluid from a Hele-Shaw cell with a sink

It is found that the radial geometry does not stabilize the evolution of instability in the displacement of a more viscous fluid by a less viscous fluid from a circular Hele-Shaw cell with a sink. A linear analysis shows the absolute instability of the radial displacement front. The appearance of isolated fingers is observed during numerical simulations.     

Photoreduction of graphite oxide nanosheets with vacuum ultraviolet radiation

Films of graphite oxide nanosheets have been prepared by deposition from an aqueous alcohol emulsion onto a Teflon FEP substrate. The behavior of the films exposed to monochromatic vacuum UV radiation at a wavelength of 123.6 nm has been studied. It has been found that irradiation decreases the water content and the amount of hydroxyl (OH) groups and increases the concentration of double bonds in the film. At the same time, irradiation does not decrease the amount of C=O groups in the carboxyl and ketone moieties.     

Nucleation and growth of gold nanoparticles on adsorption layers and in ultrathin films of poly(2-vinylpyridine)

Peculiarities of the nucleation and growth of gold nanoparticles on adsorption layers and in ultrathin films of poly(2-vinylpyridine) (PVP) in the chemical reduction of sorbed Au(III) ions and the consequent thermal treatment of systems are studied by X-ray photoelectron spectroscopy and optical spectroscopy. It is shown that nitrogens of PVP pyridine groups coordinate gold atoms. It is revealed that, even at relatively short contact between PVP film saturated with chloroauric acid and the solution of strong reductant NaBH₄, Au(III) ions are reduced to metal. As a result, quasi-metal gold particles are formed. At the same time, when exposing a PVP-Au system to the solution of weak reductant NH₂OH, the process of reduction proceeds in several stages. First, Au(III) ions are reduced to Au(I) followed by the reduction to Au(0) as a result of disproportionation reaction. It is demonstrated for the first time that, upon using NH₂OH, the rate of reduction, as well as the structure of prepared PVP-Au nanocomposite films depends to substantial extent on solution pH. Prolonged annealing of ultrathin nanocomposites at 150 °C, i.e., above the glass transition temperature of polymer matrix, leads to an increase in the sizes of metal particles and the formation of systems characterized by intense absorption within the 500–600-nm range due to the localized plasmon resonance of gold nanoparticles.     

Physicochemical characteristics of the components of energetic condensed systems

The physicochemical characteristics of nanosized energetic materials (aluminum, ammonium nitrate, RDX) are studied and the burning rate of energetic condensed systems containing nanosized components is determined. The morphology, chemical purity, and thermal properties of nanosized powders produced by vacuum and plasma recondensation were examined. The materials obtained are identical to the precursors and are characterized by an increased reactivity compared to their microsized counterparts. At a pressure of 100 atm, a monopropellant prepared from nanosized RDX particles is found to have twice as high the burning velocity as a microsized RDX propellant. For nanoaluminum-ammonium perchlorate compositions, the burning velocity is demonstrated to be an order of magnitude higher than that for similar compositions with microsized aluminum. An important feature of nanoaluminum-based formulations is a decrease in the degree of agglomeration of metal fuel products and, hence, in two-phase losses in solid-propellant rocket engines.     

C<Subscript>60</Subscript> fullerene decoration of carbon nanotubes

A new fully carbon nanocomposite material is synthesized by the immersion of carbon nanotubes in a fullerene solution in carbon disulfide. The presence of a dense layer of fullerene molecules on the outer nanotube surface is demonstrated by TEM and XPS. Fullerenes are redistributed on the nanotube surface during a long-term action of an electron beam, which points to the existence of a molecular bond between a nanotube and fullerenes. Theoretical calculations show that the formation of a fullerene shell begins with the attachment of one C₆₀ molecule to a defect on the nanotube surface.     

Contact Properties and Surface Structure of Polypyromellitimide Films Modified by Direct-Current Discharge

High Energy Chemistry - The contact properties, chemical structure, and surface morphology of polypyromellitimide films modified at the cathode and anode by dc discharge have been investigated. A...