Radical copolymerization of sodium 2-acrylamido-2-methylpropane sulfonate and sodium acrylate in water-alcohol solutions

The effect of the nature of a solvent on the kinetic parameters of the process and the intrinsic viscosities of copolymers formed by the homogeneous free-radical copolymerization of the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid and the sodium salt of acrylic acid initiated by potassium persulfate in water, water-methanol mixtures (92: 8, 84: 16, 75: 25, 50: 50), and water-isopropanol (50: 50) mixtures at pH 9 and 60°C is studied. The initial rate of copolymerization increases with increases in the concentrations of the comonomers and initiator, the content of 2-acrylamido-2-methylpropane sulfonic acid in the initial monomer mixture, and the content of water in a water-methanol mixture and in the sequence of solvents water-methanol < water-isopropanol. The intrinsic viscosity and yield of the copolymer grow when the content of 2-acrylamido-2-methylpropane sulfonic acid in the initial monomer mixture and water in water-methanol mixtures are increased and when isopropanol is replaced with methanol. The reactivity ratios of the monomers in water-methanol (50: 50) and water-isopropanol (50: 50) mixtures are determined.     

Energy distribution of electrons field-emitted from carbon nanoemitters

The height of an extra low-energy maximum in the energy distribution of electrons tunneling from crystalline carbon fibers and carbon nanotubes is studied as a function of emitter heating and emitter rotation relative to the energy analyzer axis. The relationships found are related to emission from electron states on the surface of the reconstructed nanocrystals and nanotubes.     

Low-energy photoluminescence of structures with GeSi/Si(001) self-assembled nanoislands

The photoluminescence spectra of structures with self-assembled GeSi/Si(001) islands are investigated as functions of the growth temperature. It is shown that the shift of the peak of photoluminescence from islands toward lower energies on decreasing the growth temperature is due to the suppression of Si diffusion into islands and an increase in the fraction of Ge in islands. A photoluminescence signal from the GeSi islands is found in the region of energies down to 0.6 eV, which is considerably smaller than the band-gap width in bulk Ge. The position of the peak of photoluminescence from islands is described well by the model of a real-space indirect optical transition with account of the real composition and elastic strains of the islands. Mono-and multilayer structures are obtained with self-assembled GeSi/Si(001) nanoislands exhibiting a photoluminescence signal in the region 1.3–2 μm at room temperature.     

The influence of a small gas addition to the structure of gas-liquid downward flow in a tube

A study of the local structure of the turbulent gas-liquid bubble flow in a tube with an inner diameter of 20 mm was performed by using the electrodiffusion method. A special feature of this research is the relatively small (up to 5% of the volume) quantities of gas added to the flow. To determine the radial distribution of the liquid velocity, its pulsations, and the local void fraction, we used a sensor of the blunt nose type, which simultaneously functioned as an electrochemical sensor and a conductivity sensor. It was shown that adding even small quantities of gas into the flow leads to a change in the liquid velocity profile in comparison with the single phase flow and rearrangement of the turbulent structure of the flow.     

Quantum-chemical study of the electronic structure of adamantane and the 1-adamantyl cation,anion, and radical

The spatial and electronic structures of the adamantane molecule (AdH), the 1-adamantyl radical (1-Ad^.), the 1-adamantyl cation (1-AD⁺), and the 1-adamantyl anion (1-Ad^–) have been calculated by the SCF-MO-LCAO method in the all-valence-electron MINDO approximation. The calculated heats of formation attest to the fact that the homolytic cleavage of the C-H bond is energetically most advantageous in the gaseous phase or in nonpolar inert solvents. The formation of a 1-Ad^–, H⁺ pair is associated with the largest expenditure of energy due to the large ionization potential of the hydrogen atom.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 357–360, May–June, 1989.     

Influence of substituents in pyrrole rings on electronic structure and molecular electrostatic potentials of porphyrins

The distributions of the molecular electrostatic potential in the central cavities of the free bases protoporphyrin IX, mesoporphyrin IX, etioporphyrin III and of their mono- and dianions have been calculated. An analysis has been made of the influence of substituents in the pyrrole rings of the investigated porphyrins on the potential distribution in their central cavities and the possible mechanism for addition of protons to the appropriate dianions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 335–339, May–June, 1988.