151Eu Mössbauer study of luminescent Y2O3:Eu3 + core-shell nanoparticles

¹⁵¹Eu Mössbauer spectroscopy was applied to distinguish among different Eu microenvironments and phases in spherical Y₂O₃:Eu^3?+? and core-shell Y₂O₃@Eu^3?+? phosphor nanoparticles prepared by using homogeneous precipitation method. ¹⁵¹Eu isomer shift revealed that Eu atoms exist only in oxidation state Eu^3?+? in all spherical and core-shell phosphors. Significant differences have been found between the Mössbauer parameters (isomer shift, principal component of EFG and linewidth) characteristic of spherical Y₂O₃:Eu^3?+? and core-shell Y₂O₃@Eu^3?+? phosphor nanoparticles. The Mössbauer parameters of spherical Y₂O₃:Eu^3?+? were associated with Eu substituting Y in the Y₂O₃, while Mössbauer parameters of core-shell Y₂O₃@Eu^3?+? phosphor were attributed to Eu being in the Eu₂O₃ shell, proving the structural model and the successful preparation of these phosphors.     

On approximate mathematical modeling of the vapor–liquid coexistence curves by the Van der Waals equation of state and non-classical value of the critical exponent

Van der Waals equation of state as well as power laws and critical exponent theories are prototypes to study the cubic shape, asymmetries and “flatness” of the vapor–liquid equilibrium curves near the critical point. In this work we study two similar methods to determine the phase curves in analytical form, which differ from each other by simplicity of mathematical calculation. We analyze temperature dependence of the coexistence curves asymptotically close to the vapor–liquid critical point. We explain the novelty of our method with respect to the standard thermodynamic limit discussed in the literature. Therefore we show that the shape of the coexistence curves can strongly influence the accepted value of the critical exponent. The results of theoretical studies have been compared with the ones obtained by experimental methods.     

Model study on steady heat capacity in driven stochastic systems

We explore two- and three-state Markov models driven out of thermal equilibrium by non-potential forces, to demonstrate basic properties of the steady heat capacity based on the concept of quasistatic excess heat. It is shown that large enough driving forces can make the steady heat capacity negative. For both the low- and high-temperature regimes we propose an approximative thermodynamic scheme in terms of “dynamically renormalized” effective energy levels.     

17O and 33S nuclear magnetic shielding of sulfur trioxides from the experimental measurements and theoretical calculations

In a recent ¹⁷O NMR spectra of liquid sulfur trioxide, several unexpected peaks appeared with the temperature‐dependent integrated peak ratio. In order to interpret NMR spectra and assign peaks to possible molecular structures, the theoretical quantum mechanical density functional theory and Møller–Plesset second‐order perturbation theory calculations were performed. It is suggested that in the liquid sulfur trioxide, apart from monomeric SO₃, a significant amount of (SO₃)₃ cyclic trimers should appear. No theoretical data support hypothesis on (SO₃)₂ dimers formation. Copyright © 2014 John Wiley & Sons, Ltd.     

Fractional electrical model for modified bismuth oxide

Modified bismuth oxide (Bi₂O₃) is of great importance to fuel cells and oxide varistors. The electrical parameters of Bi₂O₃ vary with its modifying components as well as with its aging temperature. This paper presents an analysis of impedance test results carried out to find an equivalent electric model and the relationship between the model's elements to various additives used to modify Bi₂O₃ and to changes in aging temperature. The proposed model was tested via computer simulation and the model parameters correlated to individual modifiers.     

Formation of Chiral β-Silyl-Vinyl Ethers

Chiral formates derived from propane-1,2-diol, 1,2- O -isopropylidene- f - D -xylo- and f - D -gluco-furanoses were subjected to treatment with cyclopentadienyl [tris(trimethylsilylmethyl)] titanium (IV). A mixture of the corresponding ( E )- and ( Z )- g -silylvinyl ethers were obtained with predominance of the former. It was found that in contrast to ( Z )-vinyl ethers, which give g -lactams with chlorosulfonyl isocyanate, the ( E )-vinyl ethers gave unstable cycloadducts which undergo rapid elimination reaction leading to ( E )- f , g -unsaturated amides.     

A new type of cation‐exchange polymeric microspheres with pendant methylenethiol groups

Synthesis and characterization of the new styrene microspheres with pendant methylenethiol groups are presented. At the first stage, the polymeric matrices were obtained by the suspension–emulsion polymerization of monomers: styrene (St) with 2,3‐(2‐hydroxy‐3‐methacryloyloxypropoxy)naphthalene (NAF.DM) or (bis[4(2‐hydroxy‐3‐methacryloyloxypropoxy)phenyl]sulfide (BES.DM) or divinylbenzene (DVB). At the second stage, the modification of the sythesized matrices was performed as follows: the matrices were reacted with paraformaldehyde in the presence of hydrochloric acid forming chloromethyl derivatives. Next, by reaction with thiourea, a thiouronium salt was obtained, and then the hydrolysis with NaOH solution and acidification with HCl were carried out. Finally, microspheres with –CH₂SH groups on their surface were obtained. The –SH group content (elemental analysis), thermal properties (thermogravimetric analysis), Fourier transform infrared as well as the swelling characteristics of the functional microspheres were examined. The surface texture was also visualized by the atomic force microscopy (AFM) method. The obtained polymers were screened towards sorption of Cu(II) ions. It was found that a better correlation between the experimental Cu(II) uptake and the theoretical curves predicted by the Langmuir or Freundlich models is obtained in the case of the DVB–St–SH polymer. In the case of the BES.DM–St–SH and 2,3‐NAF–St–SH ones, the Freundlich model corresponded quite well to the experimental data. Copyright © 2013 John Wiley & Sons, Ltd.     

The influence of oxidation number of sulfur on the polymerization and thermo-mechanical properties of dimethacrylate copolymers

Structure and characterization of the sulfur-containing monomers bis[4(2-hydroxy-3-methacryloyloxypropoxy)phenyl]sulfide (S·DM), bis[4(2-hydroxy-3-methacryloyloxypropoxy)phenyl]sulfinyl (SO·DM), bis[4(2-hydroxy-3-methacryloyloxypropoxy)phenyl]sulfonyl (SO₂·DM), and their photopolymerization with N-vinyl-2-pyrrolidone (NVP) are presented. The monomers were obtained in the reaction of derivatives of aromatic diols with 2-(chloromethyl)oxirane in the two-phase liquid/liquid system, including organic and aqueous phases. Next, esterification of the obtained diglycidyl ether was carried out with the use of methacrylic acid. Photopolymerization of the compositions (S·DM, SO·DM, SO₂·DM and NVP) and the initiator (Irgacure 651) was carried out. The influence of oxidation number of sulfur on the properties of the obtained copolymers was studied. The following properties were determined: density, glass transition temperature, Young’s modulus, hardness and tensile strength. Additionally, dynamic-mechanical and thermal properties were investigated. Thermal properties of copolymers under different conditions (in air, in nitrogen and in helium) were tested.     

Performance of density functional theory in computing nonresonant vibrational (hyper)polarizabilities

A set of exchange‐correlation functionals, including BLYP, PBE0, B3LYP, BHandHLYP, CAM‐B3LYP, LC‐BLYP, and HSE, has been used to determine static and dynamic nonresonant (nuclear relaxation) vibrational (hyper)polarizabilities for a series of all‐trans polymethineimine (PMI) oligomers containing up to eight monomer units. These functionals are assessed against reference values obtained using the Møller–Plesset second‐order perturbation theory (MP2) and CCSD methods. For the smallest oligomer, CCSD(T) calculations confirm the choice of MP2 and CCSD as appropriate for assessing the density functionals. By and large, CAM‐B3LYP is the most successful, because it is best for the nuclear relaxation contribution to the static linear polarizability, intensity‐dependent refractive index second hyperpolarizability, static second hyperpolarizability, and is close to the best for the electro‐optical Pockels effect first hyperpolarizability. However, none of the functionals perform satisfactorily for all the vibrational (hyper)polarizabilities studied. In fact, in the case of electric field‐induced second harmonic generation all of them, as well as the Hartree–Fock approximation, yield the wrong sign. We have also found that the Pople 6–31+G(d) basis set is unreliable for computing nuclear relaxation (hyper)polarizabilities of PMI oligomers due to the spurious prediction of a nonplanar equilibrium geometry. © 2013 Wiley Periodicals, Inc.