Sizes and fluorescence of cadmium sulfide quantum dots

Cadmium sulfide quantum dots have been synthesized by wet chemical deposition from an aqueous solution. The sizes of the quantum dots determined by dynamic light scattering directly in the colloidal solution and by intermittent-contact atomic force microscopy in the dry sediment agree with each other. It has been found that splitting of the fluorescence peaks of the quantum dots can be affected by the disorder of the atomic structure of cadmium sulfide quantum dots.     

Electronic structure and stability of nonstoichiometric titanium monoxide TiO y with structural vacancies in one of the sublattices

The electronic structure of nonstoichiometric titanium monoxide TiO _y with different compositions y, which contains structural vacancies either in the metallic sublattice or in the nonmetallic sublattice, has been investigated using the supercell method within the DFT-GGA approximation with pseudopotentials. The cases of ordered and disordered arrangements of vacancies have been considered. It has been found that the complete removal of vacancies from the sublattice is energetically unfavorable, and the ordering of oxygen vacancies according to the type of the Ti₆O₅□₁ superstructure, as well as titanium vacancies according to the Ti₅?₁O₆ type, does not lead to the stabilization of the B1 basic structure of titanium monoxide.     

Hybrid Mn–iXn –i superstructures in compounds with atomic vacancy ordering

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Direct functionalization of the C—H bond in (hetero)arenes: aerobic photoinduced oxidative coupling of azines with aromatic nucleophiles (SNH-reactions) in the presence of a CdS/TiO2 photocatalyst

A highly selective coupling of azines with aromatic nucleophiles (S_N^H-reactions) in the presence of a heterogeneous oxidation system O₂/CdS/TiO₂ upon exposure to daylight was accomplished.     

Magnetic properties of a monocrystalline quasicrystal in the Al-Pd-Mn system

Magnetic susceptibility of a monocrystalline icosahedral Al_70.2Pd_21.3Mn_8.5 quasicrystal was measured over the temperature range from 4 to 1100 K. The susceptibility was found to include the temperature-independent diamagnetic contribution, the temperature-dependent Curie’s contribution, and the contribution from the Pauli paramagnetism of an electron system with energy gap. An analysis of the low-temperature susceptibility revealed the presence of about 0.008% of ions with magnetic moment 4µ_B in the quasicrystal at 4 K. It is assumed that the ions with uncompensated magnetic moments appear near the structural vacancies in the quasicrystal lattice. The energy gap between the valence and conduction bands is estimated at Δ=0.64 eV, and the effective mass of charge carriers is equal to approximately 70 electron masses.     

Copolymerization of Ethylene and Propylene Using Silicon Tetrachloride‐Modified Silica/MAO with Et[Ind]2ZrCl2 Metallocene Catalyst

For the copolymerization of ethylene with propylene or a higher α‐olefin, using Et[Ind]₂ZrCl₂ metallocene catalyst, modification of silica with silicon tetrachloride prior to MAO adsorption can increase the activity, which is more pronounced for ethylene/1‐hexene copolymerization at higher pressure and temperature. The molecular weight of the copolymer produced was lower and the polydispersity tends to be decreased. No significant effect of SiCl₄ addition on the microstructure and the chemical composition distribution of the copolymer produced was observed.     

A parametric study of the terminal maleation of polypropylene through an Alder Ene reaction

A study of the parameters that affect the Alder Ene reaction with respect to the synthesis of a terminally anhydride-functionalized polypropylene was carried out over a temperature range of 220–250°C using maleic anhydride concentrations of 2–12 mol equivalence with respect to the vinylidene group. As previously observed, a Lewis acid (i.e., SnCl₂ · 2H₂O) had a catalytic effect on the reaction at these temperatures, thereby improving anhydride content in the polymer for short reaction times. Increased temperature and maleic anhydride concentration had a positive effect on improving the incorporation of the succinyl anhydride moiety at the terminal site in polypropylene. Lower SnCl₂ · 2H₂O concentrations, likewise, improve the functionality of the product. The application of a second-order kinetic model to the measured succinyl anhydride results was not valid over the entire temperature range studied due to side reactions, particularly vinylidene isomerization, and homopolymerization of maleic anhydride. Ruthenium chloride has been examined as another possible catalyst candidate in the reaction and has been found to improve the level of anhydride incorporation in polypropylene compared to stannous chloride. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2371–2380, 1998     

Synthesis of Poly(methyl methacrylate) Nanosize Particles by Differential Microemulsion Polymerization

Poly(methyl methacrylate) nanosize particles were synthesized by a differential microemulsion polymerization process. Sodium dodecylsulfate and ammonium persulfate were used as the surfactant and initiator, respectively. The effects of reaction conditions on the particle size have been investigated. A particle size of less than 20 nm in diameter has been achieved with surfactant/monomer and surfactant/water weight ratios of 1:18 and 1:120, i.e. much milder conditions than those previously reported in the literature.

TEM image of nanoparticles prepared via differential microemulsion polymerization.     

Synthesis of tailor‐made polyethylene through the control of polymerization conditions using selectively combined metallocene catalysts in a supported system

Tailoring of the molecular weight distribution (MWD) in ethylene polymerization was attempted by selectively combining different types of metallocene catalysts onto a single support. The catalyst produced by supporting Et[Ind]₂ZrCl₂ and Cp₂HfCl₂ onto a single MAO pretreated silica support was able to produce polymers with unimodal or bimodal MWD's. This approach permits the synthesis of polyethylene with different MWD's using the same catalyst as a function of the polymerization conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 331–339, 1999     

Superposition of M<Subscript>5</Subscript>X<Subscript>5</Subscript> superstructures and X-ray diffraction in TiO<Subscript>1.0</Subscript> titanium monoxide

The interpretation of diffraction spectra of ordered high-temperature phases of solid solutions and strongly nonstoichiometric compounds is discussed. It has been shown that variations of the intensities of superstructure reflections, which cannot be explained within simple ordering models, can be due to the superposition of superstructures with different symmetries in the matrix of the basis crystal structure. Using an example of atom–vacancy ordering in TiO_1.0 titanium monoxide, a model of the order–order transition state formed by the superposition of low-temperature monoclinic (space group A2/m (C2/m)) and high-temperature cubic (space group Pm3?m) M₅X₅ superstructures has been proposed. It has been shown that the transition state is thermodynamically equilibrium and should be implemented instead of the M₅X₅ cubic superstructure. The transition state model can be considered as an M_(5–i)X_(5–i) superstructure (i = 1, 14/18, 11/18) with the monoclinic symmetry (space group P1m1).