Aqueous phase behavior of ionic liquid-related gemini surfactant revealed by differential scanning calorimetry and polarized optical microscopy

An aqueous phase behavior was investigated for ionic liquid-related cationic gemini surfactant, [C₁₂im-4-C₁₂im][Br₂], in which two dodecylimidazolium parts are linked by a spacer composed of four methylene units. Differential scanning calorimetry was used to detect phase boundaries among various phases, from which a temperature−composition (T−X) phase diagram was constructed. Lyotropic liquid-crystalline phases appearing in this mixture were characterized by means of polarized optical microscopy. It was revealed that (1) two types of liquid-crystalline phases, lamellar (L_a {{\hbox{L}}_\alpha } ) and hexagonal (H₁), are formed; (2) H₁ phase coexists with micellar solution (L₁) over a wide concentration range from a few wt.% to ca. 80 wt.% of the surfactant; and (3) the hydrated solid with the composition of [C₁₂im-4-C₁₂im][Br₂]·2H₂O exhibits incongruent melting point at which the hydrated solid decomposes into H₁ phase and unhydrated surfactant solid.     

Determination of triplet quantum yields by laser flash absorption spectroscopy

A general method based on a relative actinometry using the laser flash spectroscopy technique has been developed for the determination of the quantum yield of triplet state formation φ,_T. φ,_T values for 17 aromatic compounds in cyclohexane or benzene at room temperature have been obtained in good agreement with previous measurements. Triplet-triplet extinction coefficients necessary for the φ,_T calculations and determined via energy transfer are also reported. Conditions of application and limitations of this method are outlined.     

Molecular structure of bis(dipyrrolylmethanates) of d-metals according to the quantum chemical calculations by the PM6 method

Quantum chemical calculations of the molecular structure of bis(dipyrrolylmethanates) of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), and mercury(II) of the composition [M₂L₂] are performed using the PM6 method within the Gaussian 09W program package. The lengths of M-N coordination bonds, the values of dihedral angles formed by N-M-N bonds, the distances l _M?M between the M?M atoms are optimized. It is noted that the regularities obtained from the analysis of the results of quantum chemical calculations of the molecular structure of [M₂L₂] helicates reliably reflect the main trends of changes in their physicochemical properties depending on the nature of a complexing agent and the features of the ligand structure.     

Theory of phase diagrams described by thermodynamic potentials with T d symmetry

Phase diagrams of crystals induced by irreducible representations with symmetry group \(L = \bar 43m\) (T _d ) are constructed within the phenomenological theory of second-order phase transitions. A model of the Landau thermodynamic potential is studied, state equations of all symmetry-conditioned phases are obtained, and general conditions for their thermodynamic stability are formulated. Equations for the boundaries of phase areas and lines of phase transitions are obtained for the fourth order of expansion of the potential via components of the order parameter. Some types of the collapse of the multicritical point of the phase diagram for the eighth order of potential expansion are studied using computer calculations. The possible existence of phase diagrams that contain one or more triple points and areas of existence of three and four phases is shown for the first time for the potentials with the above symmetry. Examples are given of crystals that undergo phase transitions in the considered symmetry of the order parameter.     

Application of Liquid State Models for the Time Efficient Phase Equilibrium Calculation of Supercritical CO2 and H2O at High Temperatures and Pressures

There are numerous models available to compute phase equilibrium composition of supercritical CO₂ and H₂O at high temperatures and pressures. In this paper a different approach is proposed where liquid state models (LSM) are used following liquid–liquid equilibrium (LLE) flash calculation in order to obtain phase compositions (solubility of CO₂ in the H₂O rich phase and that of H₂O in the CO₂ rich phase). Four LSM (two two-parameter models UNIQUAC and LSG, and two three-parameter models NRTL and GEM-RS) are investigated. The original forms of these models are inappropriate to represent the literature values; the binary interaction parameters are related with both pressure and temperature. These modified versions are suitable to generate phase composition values within 2–7 % deviation. Further investigations show that the LLE calculation is more time efficient than vapor–liquid equilibrium computation, meaning our approach can save computational expense for the numerical simulation of CO₂ flows in a reservoir. Comparison of the time efficiency of these LSM models with respect to other equations of state is given.     

Structure and Magnetic Characteristics of New Binuclear Complexes Based on Bisbenzoylhydrazones of 2,6-Diformyl-4-R-phenols and Copper(II) Nitrate

A series of binuclear Cu(II) complexes with bisbenzoylhydrazones of 2,6-diformyl-4-R-phenols (R = OCH₃, CH₃, CH₂Ph, Cl, Br, CO₂CH₃) with H₂LCu₂(NO₃)₂(OCH₃) composition, where H₂L^–are monodeprotonated bishydrazones, was synthesized. The structure of the obtained complexes was established using IR spectro-scopy and conductometric and magnetochemical data. The title complexes were shown to exhibit exchange interaction of the antiferromagnetic type. Results of quantum-chemical calculations of structures modeling the state of a ligand in the complex were used to discuss the effect of substituent R nature on magnetic exchange in the complexes.     

Fluid phase stability and equilibrium calculations in binary mixtures: Part II: Application to single-point calculations and the construction of phase diagrams

The methodology presented in Part I of this work is applied to a large number of pressure–temperature flash calculations, and to the automated construction of constant temperature pressure–composition phase diagrams, and constant pressure temperature–composition phase diagrams for binary mixtures modeled with an augmented van der Waals equation of state. An automated prototype implementation of the algorithm is developed for this purpose. We follow the classification of Scott and van Konynenburg [R.L. Scott, P.H. van Konynenburg, Discuss. Faraday Soc. 49 (1970) 87] and present phase diagrams corresponding to non-azeotropic mixtures of the five main types of fluid phase behavior (I–V), studying in detail representative diagrams at constant pressure and constant temperature. Special attention is given to the solution of numerically problematic equilibrium regions, such as those close to three-phase equilibria where metastable and unstable critical points can also be found. Of the order of 10⁴ flash calculations at varying temperatures and pressures, and for different intermolecular parameters of the components in the mixture, have been carried out. The algorithm provides the correct stable equilibrium state for all of the points considered. Despite the fact that our implementation is not optimised for performance, we find that the algorithm identifies the stable solution in difficult regions of the phase space without any penalty in terms of computational time, when compared to simpler regions.     

Carbon Species and Precise Elemental Analysis of Precursors for Superconducting (Bi,Pb)2Sr2Ca2Cu3Ox Tapes

 The chemical composition of BiPbSrCaCuO precursors prepared by different syntheses has to be checked analytically before further application to production of superconducting (Bi,Pb)₂Sr₂Ca₂Cu₃O_x tapes. Carbon species in concentrations below 0,1%(w/w) were observed to be possibly a source of gas evolving reactions during the heat treatment procedures for the superconducting phase formation. A method that allows the temperature controlled detection of CO₂ resulting from reactions of various carbon species was developed based on an commercial C/H₂O-analyser with IR gas detectors. By means of this method it is possible to relate the carbon content to the conditions of synthesis and technological steps of the tape production. The phase formation mechanism of the superconducting (Bi,Pb)2223 phase from a multiphase precursor strongly depends on its elemental composition. Titrimetric and ICP spectrometric methods that allow the determination of the content of the main components Bi, Pb, Ca, Sr, and Cu with high precision and accuracy were developed and their results were compared. The best results were obtained with a combined chemical-spectrometric procedure. The relative standard deviations (RSD) for all metallic elements do not exceed 1%. The analytical results of the main components and specific trace determinations are essential for the functioning of superconducting tapes.     

Stoichiographic determination of the composition and concentration of phases encapsulated in the bulk of a solid matrix phase

A two-step method of stoichiographic calculations used in the determination of the formulas of phases encapsulated in the bulk of matrices of another composition is proposed. At the first stage of calculations, the stoichiometric composition of the encapsulated phase is determined and, at the second step, the concentrations of this phase and the matrix are found. The use of this method in the analysis of oxide La–Cu catalysts by the method of differential dissolution ensures the detection of the phase La₁Cu₁ (La₂Cu₂O₅), incorporated within the matrix La₁Cu_0.5 (La₂CuO₄) phase.     

ZrO2球的准气相反应合成

提出了一种工艺简单、成本低廉的准气相反应合成ZrO₂球的新方法. 通过对产物的SEM观测表明: 该方法制备的ZrO₂粒子为较好的球形, 球表面光滑; 其平均粒径1.71 μm, 标准偏差0.49 μm; 球有三种结构: 均匀致密结构、核心疏松外层致密结构和空心结构; 经600 ℃煅烧后, XRD分析确定ZrO₂球的相组成主要为立方相.     

Molecular Structure,Thermodynamic and Spectral Characteristics of Metal-Free and Nickel Complex of Tetrakis(1,2,5-thiadiazolo)porphyrazine

The Knudsen effusion method with mass spectrometric control of the vapor composition was used to study the possibility of a congruent transition to the gas phase and to estimate the enthalpy of sublimation of metal-free tetrakis(1,2,5-thiadiazolo)porphyrazine and its nickel complex (H₂TTDPz and NiTTDPz, respectively). The geometrical and electronic structure of H₂TTDPz and NiTTDPz in ground and low-lying excited electronic states were determined by DFT calculations. The electronic structure of NiTTDPz was studied by the complete active space (CASSCF) method, following accounting dynamic correlation by multiconfigurational quasi-degenerate second-order perturbation theory (MCQDPT2). A geometrical structure of D_2h and D_4h symmetry was obtained for H₂TTDPz and NiTTDPz, respectively. According to data obtained by the MCQDPT2 method, the nickel complex possesses the ground state ¹A_1g, and the wave function of the ground state has the form of a single determinant. Electronic absorption and vibrational (IR and resonance Raman) spectra of H₂TTDPz and NiTTDPz were studied experimentally and simulated theoretically.     

A Novel Metastable Pentavalent Plutonium Solid Phase on the Pathway from Aqueous Plutonium(VI) to PuO2 Nanoparticles

Here we provide evidence that the formation of PuO₂ nanoparticles from oxidized Pu^VI under alkaline conditions proceeds through the formation of an intermediate Pu^V solid phase, similar to NH₄PuO₂CO₃, which is stable over a period of several months. For the first time, state‐of‐the‐art experiments at Pu M₄ and at L₃ absorption edges combined with theoretical calculations unambiguously allow to determine the oxidation state and the local structure of this intermediate phase.     

Synthesis and characterization of FePt nanoparticles and FePt nanoparticle/SiO2-matrix composite films

Superparamagnetic face-centered cubic (fcc) FePt nanoparticles were synthesized using a polyol process. The effect of reaction temperature and molar ratio of Fe(CO)₅ to Pt(acac)₂ on the structure, composition and morphology of nanoparticles has been investigated. The optimum processing condition has been obtained for producing well-monodisperse fcc-phase FePt nanoparticles with the 2:1?molar ratio of Fe-Pt at 220?°C. In order to circumvent the problem of FePt particle coalescence during high temperature annealing for the L1₀ ordering, FePt nanoparticle/SiO₂-matrix composite films have been fabricated by sol?Cgel method. The experimental results confirm that the amorphous SiO₂ matrix effectively inhibits the grain growth and particle aggregation during 700?°C annealing for 1?h. Well-monodisperse face-centered tetragonal (fct) FePt particles embedded in the SiO₂ matrix can be obtained with the long-range chemical order parameter S of ~0.74, indicating partially ordered L1₀ phase transition in FePt/SiO₂ composite films. The FePt/SiO₂ system exhibits a hysteretic behavior with smaller coercive field of 1,450 Oe. The incomplete phase transition from cubic deredat height maxsium (A ₁-disordered phase to tetragonal L1₀-ordered phase) might be responsible for it.     

Editorial

Stability analysis is suggested as a preliminary step in isothermal flash calculations, and a number of numerical methods for stability analysis based on Gibbs' tangent plane criterion are described. These methods, which are applicable for both single phase and multiphase systems, are developed mainly for Equation of State calculations using a single model for all fluid phases. Special adaptions ensuring convergence in critical regions are discussed.     

Electrochemical Selective Determination of Uranyl Ions Using PVC Membrane Sensor

A UO₂²⁺‐PVC membrane electrode was constructed using 2‐thenoyltrifluoroacetone as ionophore and its electrochemical response performance was characterized. The effect of membrane composition on the electrode performance was studied and best results were obtained using dioctylsebacate as a mediator and potassium tetrakis(4‐chlorophenyl)borate as anion excluder. The optimized UO₂²⁺‐sensor exhibited a Nernstian response with a slope of 29.5±0.5 mV decade⁻¹ over the concentration range 5.0×10⁻⁷−1.0×10⁻¹ mol L⁻¹ at 25 °C with a detection limit of 3.1×10⁻⁷ mol L⁻¹. The optimized electrode showed very good selectivity towards UO₂²⁺ relative to a wide variety of other cations and fast response time. Surface morphology of the optimized membrane electrode at different stages of its development and use was investigated and discussed. Quantum chemical calculations for geometrical optimization of the ionophore were carried out to investigate the interaction between the ionophore and UO₂²⁺ using DFT B3LYP/6‐31++G(d,p) level of theory and the obtained data confirmed the proposed response mechanism. The developed sensor was successfully applied for UO₂²⁺ selective determination in real water samples and the obtained results were compared to those obtained by spectrophotometric method indicating no significant difference.     

Reaction of ZnCl2 and HgCl2 metal salts with a bidentate Schiff base ligand in methanol solution, X-ray crystal structure, and theoretical studies

From the reaction of ZnCl₂ and HgCl₂ metal salts with (E)-4-chloro-N-(pyridine-2-ylmethylene)benzeneamine (L) in methanol solution, two binuclear Schiff base complexes were prepared. Both complexes were characterized by elemental analysis, UV–Vis, and IR spectrophotometry. X-ray crystal structure analysis showed that metal ion in the resulting centrosymmetric dinuclear ML₂Cl₄ complexes is in a distorted trigonal bipyramidal and a distorted square pyramidal coordination environment in the case of Zn(II) and Hg(II) metal ions, respectively. Three types of reaction between MCl₂ salts and ligand L producing three different types of products—ML₂ ²⁺, MLCl₂, and M₂L₂Cl₄—were simulated in both the gas phase and solution. The gas phase calculations at DFT (B3LYP) level of theory using SDD, CEP-121G, and LanL2DZ basis sets showed that the binuclear M₂L₂Cl₄ complexes are more stable than corresponding mononuclear MLCl₂ complexes. Furthermore, both the gas phase and solution studies showed that the formation of M₂L₂Cl₄ complexes from the metal cations, chloride anion, and ligand molecule is energetically more favored than that of MLCl₂ and ML₂ ²⁺ complexes.     

Magnetic resonance in Cu(hfac)2LR heterospin chain polymer complexes

Cu(hfac)₂ chain polymer heterospin complexes with pyrazole-substituted nitronylnitroxides (L^R, where R = Me, Et) with a composition Cu(hfac)₂L^R, exhibiting structural rearrangements with magnetic effects in the solid state at reduced temperatures, were studied by magnetic resonance. The magnetic resonance spectrum changes substantially for substituents of different types. The results of this study are discussed in the context of the cluster approach in view of the specific crystal structure of the compounds.     

Time-property least-squares spectral method for population balance equations

In multiphase chemical reactor analysis the dispersed phase distribution plays a major role in obtaining reliable predictions. The population balance equation is a well established equation for describing the evolution of the dispersed phase. However, the numerical solution of this type of equations is computationally intensive. In this work, a time-property least squares spectral method is presented for solving the population balance equation including breakage and coalescence processes. In this problem, both property and time are coupled in the least squares minimization procedure. Spectral convergence of the L ² least squares functional and L ² error norms in time-property is verified using a smooth solution to the population balance equation.     

Pressure‐induced Oxidation State Change of Ytterbium in YbGa2

The crystal structure and the electronic properties of YbGa₂ realising a CaIn₂ type atomic arrangement were characterised at ambient conditions using single crystal X‐ray diffraction data and magnetic susceptibility measurements at ambient pressure. Pressure‐induced changes of structural and electronic properties of YbGa₂ were measured by means of angle‐dispersive X‐ray powder diffraction and XANES at the Yb L_III threshold. At pressures above 22(2) GPa, YbGa₂ undergoes a structural phase transition into a high pressure modification with a UHg₂ type crystal structure. Parallel to the pressure‐induced structural alterations, ytterbium in YbGa₂ undergoes an increase of the oxidation state from +2 at ambient conditions to +3 in the high‐pressure phase. Quantum chemical calculations of the Electron‐Localisation‐Function confirm that the phase transition is associated with a conversion of the three‐dimensional gallium network of the low‐pressure crystal structure into two‐dimensional gallium layers in the high‐pressure modification.