Reaction of benzylidenetriphenylphosphorane with 1,4-dichloro-3а,6а-diaza-1,4-diphosphapentalene

The transylidation between 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalene and benzylidenetriphenylphosphorane (Ph₃P=CHPh) results in either mono- or disubstitution of chlorine atoms by the Ph₃P=C(Ph) group depending on the reactant molar ratio. In the crystal, the monosubstituted product has the planar diazadiphosphapentalene ring and the P—Cl ionic bond. The ³¹P NMR spectra of this compound exhibit a strong solvent-dependent behavior, which indicates that it exists both in the ionic form (in CH₂Cl₂, MeCN) and the molecular form (in THF). In the disubstituted product, the diazadiphosphapentalene skeleton is non-planar and is bent along the N—N bond.     

Mesoscopic Morphology of Proton‐Conducting Polyelectrolyte Membranes of Nafion® Type: A Self‐Consistent Mean Field Simulation

Summary: A SCMF simulation is presented for a coarse‐grained model of Nafion®. Based on a number of simplifying assumptions, this study predicts distinct morphological changes in the material upon alteration of temperature and water content. We found that the hydration level corresponding to the microphase segregation depends on the temperature of the system. Spherical clusters constituting the hydrophilic microphase of the membrane at relatively low water content (but above the transition point) grow in size, coalesce and form a network of channels responsible for the ionic transport at higher hydration levels. This hydrophilic phase is shielded from the hydrophobic matrix by the sidechains of Nafion®, their end‐groups being turned towards the water clusters. The results obtained are similar to those reported from dissipative particle dynamics studies and support the “cluster‐network” model for the low hydration levels and the “sponge” model at higher hydration levels. The simulation approach chosen proved to be effective for the mesoscopic structure analysis of the heterogeneous polymeric material.

Schematic representation of the structure of Nafion®‐water blends.     

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Bismuth nanoparticles electrooxidation: theory and experiment

The article presents the findings of microscopic and electrochemical studies of electrooxidation of bismuth particle of varying sizes. Bismuth particles were immobilized on the surface of indifferent carbon containing screen-printed electrodes. The calculations and experimental studies demonstrated that the transition from macroparticles to nanoparticles caused a shift of the maximum current potential of bismuth oxidation into the area with more negative potentials. A positive correlation between experimental and calculated data confirms once again a relevant application of the earlier proposed mathematical model and the possible use of the shift of the maximum current potential of electrooxidation to describe electrochemical activity and energy properties of metal nanoparticles.

     

AC-hopping conductance of self-organized Ge/Si quantum dot arrays

Dense (n=4×10¹¹ cm^-2) arrays of Ge quantum dots in a Si host were studied using attenuation of surface acoustic waves (SAWs) propagating along the surface of a piezoelectric crystal located near the sample. The SAW magneto-attenuation coefficient, ΔΓ=Γ(ω,H)-Γ(ω,0), and change of velocity of SAW, ΔV/V=(V(H)-V(0))/V(0), were measured in the temperature interval T=1.5–4.2 K as a function of magnetic field H up to 6 T for the waves in the frequency range f=30–300 MHz. Based on the dependences of ΔΓ on H, T and ω, as well as on its sign, we believe that the AC conduction mechanism is a combination of diffusion at the mobility edge with hopping between localized states at the Fermi level. The measured magnetic field dependence of the SAW attenuation is discussed based on existing theoretical concepts.     

Low-temperature normal-pressure CVD of carbon nanotubes from CO + H2 gas mixture: Thermodynamic analysis and experimental observation

It has been shown that the deposition of carbon nanotubes from CO could take place at very low temperatures by adding hydrogen to the gas mixture. Adding hydrogen significantly changes the nature of the chemical vapor deposition process. It has been demonstrated that at a certain ratio CO : H₂ this gas mixture on the one hand could be used for the deposition of carbon structures at low temperatures and on the other hand for the etching of carbon structures at high temperatures. Thus, the same gas mixture can be both a source of carbon and its etchant depending on temperature. We have also demonstrated that carbon nanotubes of good quality without impurities of amorphous carbon, soot or graphite can be formed from the gas mixture of CO + H₂ at low temperatures.