Liquid–liquid equilibria of copolymer mixtures based on an equation of state

Liquid–liquid equilibria of copolymer mixtures were studied by an equation of state (EoS) for chain-like fluids. The equation consists of a reference term for hetero-nuclear hard-sphere chain fluids developed by Hu et al. where the next-to-nearest-neighbor correlations have been taken into account; and a perturbation term from Alder et al.’s square-well attractive potential. The segment parameters, including number of segments, segment diameter and interaction energy between segments, are obtained by fitting pVT data of pure homopolymer. For the case of different species in the same copolymer, the interaction parameters for unlike segment pairs are obtained by fitting pVT data of pure copolymer. For the interaction between segment of homopolymer and different species in copolymer, the parameters are treated as adjustable by fitting liquid–liquid equilibria data. In the latter case, the difference between different species in a copolymer is simply neglected as an approximation. Therefore, in general, only one pair of adjustable interaction parameter is determined from LLE data. To model miscibility maps of copolymer mixtures having two or three kinds of species, the interaction parameters are obtained from the boundary between miscible and immiscible regions. The EoS used in this work can correlate phase behavior including coexistence curves, miscibility windows and miscibility maps.     

Ornstein–Zernike direct correlation function from diffraction experiments in supercooled liquid silicon and in disordered cobalt

Using experimental data for the structure factor S(q) of supercooled liquid silicon, and amorphous and supercooled liquid cobalt, we have calculated and compared the Fourier transform c(q) of the Ornstein–Zernike direct correlation function for these two systems. Differences of c(q) between Si and Co are ascribed to the different atomic coordination and packing, high in Co due to typical metallic bonding, and lower in Si due to more directional bonding. Also, in contrast to previous expectations, differences are found between the direct correlation function of amorphous and supercooled liquid cobalt.     

Low-temperature liquid–liquid extraction of phenols from aqueous solutions with hydrophilic mixtures of extractants

The volume ratios in acetonitrile–ethyl acetate (90 : 10, 95 : 5), acetonitrile–isopropanol–ethyl acetate (70 : 15 : 15, 80 : 5 : 15), and isopropanol–1-butanol (50 : 50) mixtures were determined. Their mixing with water (1 : 1) and storage at–10°C led to partitioning into two immiscible liquid phases without formation of the ice phase. The mixtures were shown to be useful as hydrophilic extractants in low-temperature liquidliquid extraction of phenol from aqueous solutions.     

Wagner liquid–vapour pressure equation constants from a simple methodology

A methodology to determine the A, B, C, and D constants from the Wagner equation is presented. The constants for 274 pure substances were determined by minimization in the sum of the squares of the relative deviation in liquid vapour pressure. For 69 chemical compounds, vapour pressures exist over the range from 1 kPa to the critical pressure and an average absolute deviation in vapour pressure of 0.039% was calculated. Using Antoine equation coefficients and initial guesses for a correlation in terms of the acentric factor, Wagner constants were estimated for substances with limited data within the range from (1 to 200) kPa. To validate the proposed methodology, vapour pressure predictions from 1 kPa to the critical pressure were made for 52 substances using Wagner parameters estimated from limited data. A value of 0.27% in average absolute deviation results for those substances. Finally the Waring criterion was applied to check the constants presented in this paper.     

Dispersive liquid–liquid microextraction using an in situ metathesis reaction to form an ionic liquid extraction phase for the preconcentration of aromatic compounds from water

A novel microextraction method is introduced based on dispersive liquid–liquid microextraction (DLLME) in which an in situ metathesis reaction forms a water-immiscible ionic liquid (IL) that preconcentrates aromatic compounds from water followed by separation using high-performance liquid chromatography. The simultaneous extraction and metathesis reaction forming the IL-based extraction phase greatly decreases the extraction time as well as provides higher enrichment factors compared to traditional IL DLLME and direct immersion single-drop microextraction methods. The effects of various experimental parameters including type of extraction solvent, extraction and centrifugation times, volume of the sample solution, extraction IL and exchanging reagent, and addition of organic solvent and salt were investigated and optimized for the extraction of 13 aromatic compounds. The limits of detection for seven polycyclic aromatic hydrocarbons varied from 0.02 to 0.3 μg L⁻¹. The method reproducibility produced relative standard deviation values ranging from 3.7% to 6.9%. Four real water samples including tap water, well water, creek water, and river water were analyzed and yielded recoveries ranging from 84% to 115%.      

On the validity of the correlation – Belda equation for some physical and chemical properties in 1,4-dioxane + water mixtures

Knowledge and prediction of physicochemical properties of binary mixtures is of great importance in understanding intermolecular interactions. The literature shows that most such systems exhibit non-linear behaviour. In this frame, a correlating equation was recently proposed by Belda and tested with success on 50 binary systems for density, viscosity, surface tension and refractive index. In order to assess the validity of the proposed equation, it has been applied to 1,4-dioxane + water mixtures at 298.15?K for nine physicochemical properties. These mixtures exhibit strong interactions. The results were fitted and compared with the Redlich–Kister (R–K) equation of the same number of parameters. The equation seems to offer better results for some properties than those of R–K with two free parameters.     

Phase separation in mixtures of thermotropic liquid crystals and flexible polymers

The spinodal equation and the concentration-induced anisotropic-isotropic transition equation of the mixtures of thermotropic liquid crystals and flexible polymers have been studied by using the molecular field theory The calculations of the phase diagrams of this system show that,besides the isotropic classic spinodal curve,there ex ists an anisotropic spinodal curve which has not been reported in literature.These two spinodal curves can be linked up by the concentration-induced anisotropic-isotropic transition line.In the various phase regions,demixing may take place due to different phase separation mechanisms.The phase equilibrium curve cannot always join the.spinodal curve at a critical point.These results are considered very meaningful for the understanding of the special properties of liquid crystal/polymer composites and very useful for controlling the morphology and the performance of PDLC materials     

Löwdin correlation energy density of the inhomogeneous electron liquid in some closed-shell molecules at equilibrium geometry

Using existing theoretical studies, we point out that the dominant variable in determining Löwdin correlation energies per electron E _c /N of isoelectronic series of molecules at equilibrium is the total number of electrons. This turns out to be E _c /N = ?0.033 ± 0.003 a.u. for CH₄, NH₃, H₂O and HF (N = 10), and E _c /N = ?0.039 ± 0.007 for some 20 Si-containing molecules in the series SiX _n Y _m . Following earlier work of March and Wind on atoms, some proposals are then made as to a possible explanation of such behaviour. A test is proposed, via low-order Møller–Plesset perturbation theory, as to whether the Löwdin correlation energy density ε _c (r) is, albeit approximately, a local functional ε _c (ρ) of the ground-state density for molecules at equilibrium. Such an LDA assumption would imply that ε _c (ρ) is quantitatively linear in ρ(r), for closed-shell molecules at equilibrium, at least for the light atomic components treated here. This, in turn implies that the dominant effect of the Löwdin correlation energy for closed-shell molecules at equilibrium is merely to shift the chemical potential.     

Phase equilibria study of Lennard–Jones mixtures by an analytical equation of state

The recently developed equation of state (EOS) for Lennard–Jones mixtures [Y. Tang, B.C.-Y. Lu, Fluid Phase Equilibria 146 (1998) 73.] is further investigated in this work for describing phase equilibria of these mixtures. The investigation covers vapor–liquid equilibria (VLE), liquid–liquid equilibria (LLE), vapor–liquid–liquid equilibria (VLLE) and vapor–vapor equilibria (VVE) over a wide range of temperatures, pressures and molecular characteristic parameters. Results from the van der Waals one-fluid (VDW1) theory are included for comparison. The newly proposed theory performs very well for VLE and LLE and the performance is better than the VDW1 theory; but both theories yield only qualitative results for VVE. It is also found that one system should exhibit VLLE, which was not noticed in previous investigations. Results from two other perturbation theories are also compared in some cases.     

One-pot synthesis of functionalized ��-acyloxythioamides from N-Protected a-amino acids as an acid component in the passerini reaction in an ionic liquid

N-Protected ??-amino acids, prepared from benzoyl chlorides, KSCN and ??-amino acids, were used as the acid component in the Passerini reaction, in an ionic liquid, to produce functionalized ??-acyloxythioamides in 59?C95% yields. The work-up procedure was fairly simple and the products did not require further purification.     

Röntgenkleinwinkelmessungen an Ferritin in Lösung

Ohne ZusammenfassungErgebnisse der vorliegenden, im wesentlichen 1959–1960 ausgeführten Untersuchungen wurden bereits mitgeteilt beiO. Kratky, Makromol. Chem.35 A, 12 (1960); Angew. Chem.72, 474 (1960);H.-J. Bielig undH. Steiner, Dissertation H. Steiner, Univ. Freiburg i. Br. 1961.     

Immobilized glycerol-based liquid membranes in hollow fibers for selective CO2 separation from CO2–N2 mixtures

Glycerol-based liquid membranes immobilized in the pores of hydrophilic microporous hollow fibers have been studied for selective separation of CO₂ from a mixed gas (CO₂, N₂) feed having low concentrations of CO₂ characteristic of gases encountered in space walk and space cabin atmosphere. The immobilized liquid membranes (ILMs) investigated consist of sodium carbonate–glycerol or glycine-Na–glycerol solution. Based on the performances of such liquid membranes in flat hydrophilic porous substrates [Chen et al., Ind. Eng. Chem. Res. 38 (1999) 3489; Chen et al., Ind. Eng. Chem. Res. 39 (2000) 2447], hollow fiber-based ILMs were studied at selected CO₂ partial pressure differentials (Δp_CO2 range 0.36–0.50 cmHg), relative humidities (RH range 45–100%), as well as carrier concentrations. The sodium carbonate concentration was primarily 1.0 mol/dm³; the glycine-Na concentration was 3.0 mol/dm³. The sweep gas was always dry helium and it flowed on the shell side. Very high CO₂/N₂ selectivities were observed with porous polysulfone microfiltration membranes as substrate. As in the case of flat film-based ILMs (see references above), feed side RH is an important factor determining the ILM performances. Generally, lower permeances and greater CO₂/N₂ selectivity values were observed at lower feed stream RHs. When the feed side average RH=60%, p_CO2,f=0.005 atm and glycine-Na concentration was 3.0 M, the CO₂/N₂ separation factor observed was over 5000. Prolonged runs lasting for 300 h showed that the hollow fiber-based ILM permeation performances were stable.     

Modification of the Furter equation and correlation of the vapor–liquid equilibrium for mixed-solvent electrolyte systems

Isobaric vapor–liquid equilibrium values at 1 atm pressure were measured for the systems 1-propanol–water–potassium acetate and 2-propanol–water–potassium acetate under fixed salt mole fractions using a modified Othmer recirculation still. A modified Furter equation, ln(α_s/α)=k₁z+k₂z², was proposed for correlating the effect of dissolved salts on vapor–liquid equilibrium (VLE). The modified equation contains two parameters that are applicable to the entire salt/solvent composition range. Correlation of VLE for 15 mixed-solvent electrolyte systems was made by means of the proposed modified equation with better results than those obtained from the original equation.     

Interaction parameter for hydrogen-containing mixtures in the Peng—Robinson equation of state

A new correlation for the Peng—Robinson interaction parameter δ_ij of hydrogen-containing mixtures is proposed here. Values of δ_ij obtained from literature vapour—liquid equilibrium data are represented by a cubic polynomial in terms of the temperature. The correlation predicts better values than other correlations proposed in the literature for the same systems, and is applicable to wider ranges of temperature. Applications of the proposed equations to VLE are presented.     

Thermodynamics for fluid mixtures near to and far from the vapor–liquid critical point

To describe thermodynamic properties of fluid mixtures near to and far from the vapor–liquid critical point, we need a method where a classical equation-of-state is augmented with a correction based on renormalization group (RG) theory. The advantage of the method described here is that, subject to well-defined assumptions, it can be applied not only to binary mixtures but to mixtures containing any number of components. While our method is based on White’s recursion procedure, our extension to mixtures is based on the isomorphism assumption and on an approximation suggested by Kiselev. To illustrate, calculations are presented for the critical loci of some alkane mixtures containing one discrete component and one pseudo-component whose composition is characterized by a continuous distribution of molecular weight. While critical loci calculated with the RG correction are similar to those calculated by the classical equation-of-state alone, inclusion of the RG correction provides better agreement with experiment.     

Dissolution of zinc oxide in a protic ionic liquid with the 1-methylimidazolium cation and electrodeposition of zinc from ZnO/ionic liquid and ZnO/ionic liquid–water mixtures

We show that zinc oxide can be dissolved in the protic ionic liquid 1-methylimidazolium trifluoromethylsulfonate, [MIm]TfO at quite a high concentration (~ 2.5 mol/L). FTIR and Raman spectra revealed the association of zinc ions with 1-methylimidazole. The ZnO/[MIm]TfO solutions and their mixtures with water were employed as electrolytes for the electrodeposition of zinc. High current density electrodeposition of zinc can be achieved in the employed electrolytes. Spongy-like zinc structures with a high porosity were obtained in ZnO/[MIm]TfO and the formation of Au_1.2Zn_8.8 alloy was observed. Compact and hexagonal zinc deposits were found in the presence of water. The present results show the potential of ionic liquids as electrolytes for rechargeable zinc–air batteries.     

New approach to the correlation problem: Electron interaction potential as a variable in solving the many-particle Schrödinger equation

The many-electron wave function is represented as the product of the wave function of the independent particles and the function that depends only on the value of the interelectron interaction potential. The function defines the electron correlation effects; a standard linear differential equation was derived to define the function. The equation depends on the functions of independent particles; a generalization of the Hartree-Fock equations including electron correlation was obtained for these functions. The total energy calculation of two-electron ions shows that even solving an ordinary differential equation for the function of independent particles represented by the functions of noninteracting electrons leads to higher accuracy than the one achieved in the Hartree-Fock theory.     

Preferential solvation of indomethacin in 1,4-dioxane + water mixtures according to the inverse Kirkwood–Buff integrals method

The preferential solvation parameters (δx_1,3) of indomethacin (IMC) in 1,4-dioxane + water binary mixtures were derived from their thermodynamic properties by means of the inverse Kirkwood–Buff integrals method. δx_1,3 is negative in water-rich and 1,4-dioxane-rich mixtures but positive in cosolvent compositions from 0.17 to 0.69 in mole fraction of 1,4-dioxane at 298.15 K. It is conjecturable that in water-rich mixtures, the hydrophobic hydration around the aromatic and methyl groups of the drug plays a relevant role in the solvation. The higher solvation by 1,4-dioxane in mixtures of similar cosolvent compositions could be mainly due to polarity effects. Finally, the preference of this drug for water in 1,4-dioxane-rich mixtures could be explained in terms of the higher acidic behavior of water molecules interacting with the hydrogen-acceptor groups present in IMC.     

Is there a relation between excess volume and miscibility in binary liquid mixtures?

Molecular dynamics computer simulations of various symmetrical Lennard-Jones (LJ) models are used to elucidate how the excess volume in dense binary liquids is related to the microscopic interactions between the particles. Both fully miscible systems and systems with a liquid-liquid phase separation are considered by varying systematically the parameters of the LJ potentials. The phase diagrams with the critical points of the demixing systems are determined by means of Monte Carlo simulations in the semigrandcanonical ensemble. The different LJ models are investigated by computing Bhatia-Thornton structure factors, enthalpy of mixing, and excess volume. For the demixing systems, the LJ models show a positive enthalpy of mixing while it is negative for the systems without miscibility gap. In contrast to that, the excess volume can be negative and positive for both demixing and fully miscible systems. This behavior is explained in terms of the interplay between the repulsive and attractive terms in the LJ potential. Whereas repulsions dominate the packing of particles as reflected by the number-density structure factor, the chemical ordering and thus the concentration structure factor are strongly affected by attractive interactions, leading to the "anomalies" of the excess volume.