Topological transformation of the cesium nitrate-water-isopropanol ternary phase diagram

Phase equilibria and critical phenomena in the cesium nitrate-water-isopropanol system, where the liquid binary subsystem does not separate over the entire temperature range of its liquid state, were studied within 70–120°C using visual polythermal analysis. The temperature at which the monotectic critical tie-line appears (79.0°C) and the compositions of the solutions at critical solution points at various temperatures were determined. Isopropanol distribution coefficients between aqueous and organic monotectic phases were calculated for five temperatures. The salting out of isopropanol by cesium nitrate from aqueous solutions is enhanced by temperature elevation. The phase isotherms validated a previously reported fragment of the general scheme of the topological transformation of ternary phase diagrams for salt-binary solvent systems with salting out. Original Russian Text ? D.G. Cherkasov, V.F. Kurskii, S.I. Sinegubova, K.K. Il’in, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 6, pp. 1032–1036.     

Phase Behavior of Aqueous Na–K–Mg–Ca–Cl–NO<Subscript>3</Subscript> Mixtures: Isopiestic Measurements and Thermodynamic Modeling

A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻ and NO₃⁻ ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 °C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 °C. The measurements have been performed using Oak Ridge National Laboratory’s (ORNL) previously designed gravimetric isopiestic apparatus, which can also detect solid phase precipitation. In addition to various Na–K–Mg–Ca–Cl–NO₃ systems, results are reported for LiCl solutions. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid–liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor–liquid and solid–liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems.     

Topological transformation of a phase diagram for the sodium nitrate-water-isopropanol ternary system

Phase equilibria and critical phenomena in the sodium nitrate-water-isopropanol ternary system, where a boundary binary liquid system shows no immiscibility over the entire temperature range of its liquid state, were studied in the range from 5 to 90°C using a visual polythermal method. The formation temperature of a monotectic critical tie-line was determined to be 6.1°C, and the solution compositions corresponding to critical solution points at various temperatures were determined. Isopropanol partition coefficients between the aqueous and organic phases of monotectic equilibrium were calculated for seven temperatures. The isopropanol salting out from aqueous solutions by sodium nitrate was shown to be enhanced by rising temperature. Isothermal phase diagrams of the title system were constructed to verify a fragment of the general scheme of topological transformations of phase diagrams for salt-binary solvent ternary systems with salting out.     

Non-ideal properties of the TRIS—TRIS·HCl−NaCl−H2O buffer system in the 0–40 °C temperature interval. Application of the pitzer equations

The buffer solution TRIS—TRIS·HCl−NaCl−H₂O was studied in the 0–40 °C temperature region and ionic strength interval of (0.1–4)m (m is molality) by the e.m.f. method using two types of cells without liquid junction composed of platinum-hydrogen, silverchloride, and sodium-glass electrodes. For temperatures of 5 and 15 °C and the (1–4)m concentration region, the osmotic coefficients of the TRIS·HCl−H₂O solutions were measured by the isopiestic method. The results were processed in the framework of the Pitzer method, and the parameters of interaction of the components of the buffer system were calculated. The associative character of the interactions in the TRIS·HCl−H₂O solution was shown. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 670–675, April, 2000.     

Clathrate formation in the liquid phase of (C4H9)4NF−NH4F−H2O

At a certain concentration of NH₄F, the solid allocyric solutions of the (C₄H₉)₄NF−NH₄F−H₂O system stratify into two liquid phases in the process of melting. The mutual solubility of the liquids decreases at elevated temperatures. The boundary surface of the stratification region was determined The solubility isotherms (27 and 30°C) of the stratification region are investigated by the solubility method This relatively rare mutual sulubility of liquids (retrograde solubility) is associated with clathrate formation in the liquid phase. Near the melting points of the solid clathrate solutions, both in the liquid and solid phases the tetrabutylammonium cation evidently forms surrounding cavities bounded by water and ammonium fluoride molecules linked by hydrogen bonds. The clathrate-like components of the solution are structurally compatible with “water-like” and “organic” components, i.e., they are homogenizing components. At higher temperatures, the homogenizing clathrate-like structures break down, and the structurally incompatible solution components stratify into two phases. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol 35, No. 6, pp. 122–128, November–December, 1994. Translated by L. Smolina     

Topological transformation of the phase diagram of the potassium nitrate-water-<Emphasis Type="Italic">n</Emphasis>-butoxyethanol ternary system

Phase equilibria and critical phenomena in the potassium nitrate-water-n-butoxyethanol ternary system were studied by the visual polythermal method over the temperature range 10–150°C. In this system, the boundary binary liquid system is characterized by the presence of a closed stratification region. The temperature of the formation of a critical tie line of monotectic equilibrium (18.3°C) and solution compositions corresponding to the critical solubility points at various temperatures were determined. The n-butoxyethanol distribution coefficients between the aqueous and organic phases of the monotectic state were calculated at eight temperatures. n-Butoxyethanol salting out from aqueous solutions by potassium nitrate increased as the temperature grew. The generalized scheme of topological transformations of salt-binary solvent ternary system phase diagrams with salting out was substantiated and augmented.     

Characterization, Solution Behavior, and Microstructure of a Hydrophobically Associating Nonionic Copolymer

To obtain an oil-displacement polymer with good thermal stability and solution properties, self-assembling acrylamide (AM)/4-butylstyrene (BST) copolymers (PSA) were synthesized by the micellar copolymerization technique. The resulting polymer was characterized by elemental analysis and UV and FT-IR spectroscopy. Conventional DSC measurement was used successfully to characterize the hydrophobic microblock structure of PSA, and two glass transition temperatures were found in the polymer: at 203 °C for the AM segments and at 106 °C for the hydrophobic BST segments. The initial decomposition temperature (234 °C) of the polymer is higher than that of polyacrylamide (210 °C). The DSC and TG results suggest that incorporation of BST into PSA enhances the molecular rigidity and thermal stability of the polymer. The apparent viscosity of a PSA solution greatly depends on the amount of BST in the polymer, and the polymer exhibits salt-thickening, temperature-thickening, thixotropy, pseudo-plastic behavior, anti shearing, and good anti-aging properties at 80 °C. In addition, the apparent viscosities of PSA solutions are increased remarkably by the addition of a small amount of surfactant. AFM measurements show that large block-like aggregates and small compact aggregates are formed in aqueous solutions of 0.4 g⋅dL⁻¹ PSA because of strong intermolecular hydrophobic associations, despite the low molecular weight, and their sizes increase upon addition of a small amount of salt.     

Influence of coagulant and free stabilizer on formation of aggregates in magnetic fluids

The influence of coagulant (isopropanol) and free oleic acid on the formation of quasi-spherical aggregates in a colloidal magnetite solution in kerosene is studied experimentally. It is revealed that the mean sizes of these aggregates fit the 60–90-nm range and are independent of the concentrations of coagulant and free oleic acid provided that these concentrations do not exceed 10–12 vol %. The independence of the mean sizes of aggregates on temperature and disperse composition of particles is considered as a supplementary argument in favor of hypothesis that the main reason for their formation are the defects of protective layers, whereas magnetodipole interactions play a secondary role. It is shown that an excess of oleic acid causes a disproportional decrease in the initial susceptibility of magnetic fluid that is interpreted as a result of the formation of droplet aggregates with characteristic sizes of a few micrometers or more. Apparently, isopropanol leads to an analogous effect, but only at low temperatures.     

Influence of ZnO on the properties of dilute and semi-dilute cellulose-NaOH-water solutions

The influence of ZnO as cellulose-8%NaOH-water solution stabilizer against gelation is studied. Cellulose intrinsic viscosity in 8%NaOH-water as a function of solution temperature is investigated in the presence and absence of ZnO. The addition of ZnO did not bring any improvement in terms of solvent thermodynamic quality. Non-dissolved ZnO particles were observed above 0.8–0.9% ZnO in 8%NaOH-water. Gelation of cellulose-8%NaOH solutions with and without ZnO are studied for various cellulose and ZnO concentrations (4–6% and 0–1.5%, respectively) in a wide range of temperatures (−5 °C to 50 °C). Gelation times were exponentially increasing with increasing ZnO concentration and with decreasing cellulose concentration and solution temperature. Gelation times of cellulose-NaOH-water-ZnO systems were found to follow a semi-empirical model correlating these three parameters. We suggest that ZnO is acting as water molecular “binder” stabilizing cellulose-NaOH-water solutions.     

Properties of cellulose films prepared from NaOH/urea/zincate aqueous solution at low temperature

Cellulose films were successfully prepared from NaOH/urea/zincate aqueous solution pre-cooled to −13 °C by coagulating with 5% H₂SO₄. The cellulose solution and regenerated cellulose films were characterized with dynamic rheology, ultraviolet–visible spectroscope, scanning electron microscopy, wide angle X-ray diffraction, Fourier transform infrared (FT-IR) spectrometer, thermogravimetry and tensile testing. The results indicated that at higher temperature (above 65 °C) or lower temperature (below −10 °C) or for longer storage time, gels could form in the cellulose dope. However, the cellulose solution remained a liquid state for a long time at 0–10 °C. Moreover, there was an irreversible gelation in the cellulose solution system. The films with cellulose II exhibited better optical transmittance, high thermal stability and tensile strength than that prepared by NaOH/urea aqueous solution without zincate. Therefore, the addition of zincate in the NaOH/urea aqueous system could enhance the cellulose solubility and improve the structure and properties of the regenerated cellulose films.     

Bi1.5ZnNb1.5O7 cubic pyrochlore ceramics prepared by aqueous solution–gel method

Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramic was successfully prepared by the aqueous solution method. The preparation, microstructure development and dielectric properties of ceramics were investigated. Homogeneous precalcined ceramics powders have a cubic pyrochlore phase after thermal treatment at the temperature as low as 450 °C. The aqueous solution–gel method, which Bi, Zn and Nb ions are chelated to form metal complexes, leading to the formation of cubic pyrochlore phase at low firing temperatures. No detectable intermediary phase such as BiNbO₄ or pseudo-orthorhombic pyrochlore is observed in the XRD patterns of ceramics at the sintering temperature range from 850 to 1,000 °C. The dielectric properties study revealed that the ceramics sintered at 900 °C show excellent performance with dielectric constant of 111 and dielectric loss of 2.3871 × 10⁻⁴ under 1 MHz at room temperature.     

Thermodynamics of neptunium(V) complexes with phosphate at elevated temperatures

The complexation of Np(V) with phosphate at elevated temperatures was studied by a synergistic extraction method. A mixed buffer solution of TRIS and MES was used to maintain an appropriate pH value during the distribution experiments. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 and 1:2 Np(V)-HPO₄ ²⁻ complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [HPO₄ ²⁻] on the distribution ratio. The thermodynamic parameters including enthalpy and entropy of complexation between Np(V) and HPO₄ ²⁻ at 25 °C–55 °C were calculated by the temperature coefficient method.     

Phase equilibria and critical phenomena in the potassium perchlorate-water-<Emphasis Type="Italic">n</Emphasis>-butoxyethanol ternary system

Phase equilibria and critical phenomena in the potassium perchlorate-water-n-butoxyethanol ternary system, where the boundary liquid binary system is characterized by the presence of a closed stratification region, were studied by the visual-polythermal method over the temperature range 40–150°C. The temperature of the formation of the critical monotectic equilibrium tie line (141.0°C) and temperature dependences of the compositions of mixtures corresponding to the critical solubility points of the stratification region over the temperature ranges 47.7–130.3 and 141.0–150.0°C were determined. The isotherms of phase states constructed at 10 temperatures were used to reveal the topological transformation of the phase diagram of the ternary system depending on temperature. At low concentrations (up to 5.8 wt %), potassium perchlorate had a salting in action on heterogeneous water-n-butoxyethanol mixtures. The solubility of the salt increased as the temperature grew, and, above 141.0°C, potassium perchlorate had a salting out action. The salting out of n-butoxyethanol from aqueous solutions by potassium perchlorate grew stronger as the temperature increased.     

Thermal stability and degradation kinetic study of white and colored cotton fibers by thermogravimetric analysis

Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO₂F(aq) and NpO₂F₂⁻, were identified by spectrophotometry in the temperature range of 10–70°C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10–70°C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature — a two-fold increase in the stability constants of NpO₂F(aq) and more than five-fold increase in the stability constants of NpO₂F₂⁻ as the temperature is increased from 10 to 70°C.     

Phase transition of aqueous solutions of poly(N,N-diethylacrylamide-co-acrylic acid) by differential scanning calorimetric and spectrophotometric methods

 The phase transition of aqueous solutions of poly(N,N-diethylacrylamide-co-acrylic acid) (DEAAm–AA) is studied by differential scanning calorimetry (DSC) and UV–vis spectrophotometry. The copolymer aqueous solutions are shown to have well-defined lower critical solution temperatures (LCSTs). The LCST values obtained from the maximum of the first derivatives of the DSC and optical transition curves agree well. DSC can be used to measure the phase-transition temperature of more dilute polymer solutions. On increasing the AA composition in the copolymers, the LCST values of the copolymer increase, then decrease at higher AA composition. For the aqueous solution of the copolymers, the transition curve obtained by the spectrophotometric method is highly wavelength dependent. The LCST values are found to be concentration-dependent. The changes in the heat of the phase transition of the copolymer solutions measured from DSC are lower than that of the homopolymer PDEAAm solution. This is consistent with the suggestion that the polymer chains of the copolymers collapsed only partially at temperatures above the LCST. The added salt (sodium chloride) decreases the transition temperature of the polymer solution. Received: 14 November 2000 Accepted: 15 January 2001     

Influence of coagulation temperature on pore size and properties of cellulose membranes prepared from NaOH–urea aqueous solution

The morphology and structure of the regenerated cellulose membranes prepared from its NaOH–urea aqueous solution by coagulating with 5 wt% H₂SO₄–10 wt% Na₂SO₄ aqueous solution with different temperatures and times were investigated. The pore size, water permeability and physical properties of the membranes were measured with scanning electron micrograph (SEM), wide X-ray diffraction (WXRD), Fourier transfer infrared spectroscopy (FTIR), flow rate method, and tensile testing. The SEM observation revealed that the structure and pore size of the membranes changed drastically as a function of the coagulation temperature. The membranes coagulated at lower temperatures tended to form the relatively small pore size than those at higher temperatures. On the contrary, the membranes coagulated at different times exhibited similar pore size. Interestingly, the mean pore size and water permeability of the membranes increased from 110 nm with standard deviation (SD) of 25 nm and 12 ml h⁻¹ m⁻² mmHg⁻¹ respectively to 1,230 nm with SD of 180 nm and 43 ml h⁻¹ m⁻² mmHg⁻¹ with an increase in coagulation temperature from 10 to 60°C. However, the membranes regenerated below 20°C exhibited the dense structure as well as good tensile strength and elongation at break. The result from FTIR and ultraviolet-visible (UV-vis) spectroscopy indicated that the relatively strong intermolecular hydrogen bonds exist in the cellulose membranes prepared at lower coagulation temperatures. This work provided a promising way to prepare cellulose materials with different pore sizes and physical properties by controlling the coagulation temperature.     

Thermodynamics of sodium diclofenac salt aqueous solutions at various temperatures

Enthalpies of solution and dilution of aqueous solutions of sodium diclofenac salt were measured by isoperibolic calorimeter at 293.15, 298.15, 303.15, 308.15 and 318.15 K. The concentration of the electrolyte was restricted to solubility salt at various temperatures and did not exceed 0.035–0.057 mol kg⁻¹ values depending on the studied temperature. The virial coefficients were derived from Pitzer’s model and the excess thermodynamic functions of both the solution and the components of the solution were calculated. The analysis of thermodynamic characteristics of the solution from concentration and temperatures was carried out and discussed.     

Physicochemical characterization of a novel surfactant peptide containing an arginine cation and laurate anion

 A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized. The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change (ΔG ⁰ _m) and standard enthalpy change (ΔH ⁰ _m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS ⁰ _m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy. From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a change at 50 °C indicating a phase change. Received: 14 February 1997 Accepted: 13 August 1997     

Dynamic light scattering experiments on thermoreversible pregels from chemically modified PVC

 Dynamic light-scattering experiments have been performed on solutions of poly(vinyl chloride) (PVC) and chemically modified PVC (HPVC) in diethyl oxalate (DEO). Hydrodynamic sizes of the clusters in the solution were measured as a function of temperature, concentration and quenching temperature. The higher the starting concentration of the PVC and HPVC solutions the larger the size of the aggregates formed. However, clusters formed by pure PVC are smaller than those formed by modified PVC. Aggregate sizes decrease with increasing temperature whereby a change in the cluster melting process is observed at 55 °C. Successive dilution of highly concentrated aggregate solutions causes reduction of the cluster size until a critical dilution concentration is reached below which no further reduction in size occurs. The lower the temperature at which the solutions are quenched the larger the clusters which are formed. We believe that all results can be interpreted using a model developed by Guenet [1–4] which describes the molecular structure of PVC/DEO gels and pregels. Received: 9 September 1997 Accepted: 2 February 1998