Russian Journal of Physical Chemistry A最新文献

A mathematical model of polymolecular adsorption developed for protein solutions at liquid–gas interfaces (V.B. Fainerman, R. Miller, et al.) is used to describe experimental concentration dependences of the change in the equilibrium surface tension and viscoelastic modulus of aqueous solutions of salts of modified humic acids and hymatomelanic acids. It is shown that experimental data are in satisfactory agreement with theoretical estimates. The polymolecular adsorption model of natural polyelectrolytes for solutions of salts of modified humic acids is used to identify correspondence between experimental data and theoretical calculations for bimolecular adsorption, and for the trimolecular adsorption of macromolecules from solutions of salts of hymatomelanic acids at interfaces with air.

The electrochemical behaviors of lithium hexafluoroarsenate-based systems in the acetonitrile (AN)–dimethyl sulfoxide (DMSO) and propylene carbonate (PC)–DMSO binary mixtures were compared. The specific electric conductivity of LiAsF₆ solutions in the AN–DMSO mixed solvent with a molal concentration of ionophore of 0.2–1.8 mol/kg and DMSO contents of 0.24–0.68 mole fractions at temperatures of 253.15, 263.15, 273.15, 283.15, 293.15, 303.15, 313.15, 323.15, and 333.15 K was determined for the first time. The concentration dependence of the specific conductivity of the test solutions obeys the Castell–Amis equation. The solvent and ionophore contributions to the activation energy of ionic conductivity were determined based on the application of the transition state theory. In the PC–DMSO and AN–DMSO mixed solvents, LiAsF₆ solutions have a narrower electrochemical window compared to that in solutions of this ionophore in the individual solvents.

Gas–liquid chromatography on a non-polar phase is used in the 393.2–473.2 K range of temperatures to determine the retention characteristics and enthalpies of sorption for 10 esters of 2,2-dimethylbutyric acid and linear alcohols C₁–C₁₀. A linear dependence of the indices of retention on temperature and the number of carbon atoms in the alcohol molecule is shown for all studied ethers. Enthalpies of evaporation are calculated, and the excess enthalpies of the mixing of ethers are determined.

The thermodynamics of γ-cyclodextrin hydration was studied using methods of thermal analysis and solution calorimetry. The enthalpy and entropy changes are in a good agreement with two steps of γ‑cyclodextrin hydration isotherm and changes of unit cell volume. The first step of γ-cyclodextrin hydration is more exothermic and has more negative change of entropy while as the second step is less exothermic providing more disorder of water molecules in the hydrate crystal. The kinetic study of γ-cyclodextrin dehydration process revealed the activation energy of this process.

Every year, the interest in obtaining new forms of phase change materials (PCM) and studying their physicochemical properties is growing. A topical task is to develop new experimental methods for studying the phase behavior of PCM. The paper presents the results of a study of the phase behavior of a nanosized aqueous dispersion of n-eicosane (C₂₀H₄₂) using an optical method. Samples of an aqueous dispersion of the studied paraffin were obtained using ultrasonic dispersion without adding surfactants. For the studied sample, the temperatures of phase transitions (melting, crystallization, rotator phases) were determined during heating and cooling. Phase transitions not observed in a bulk sample of the studied paraffin were discovered.

The study of the reactivity of heterocyclic thioamides exhibiting antithyroid activity is of scientific and practical interest. For objective evaluation of the reactivity of thioamides with biologically active and biogenic metal ions, reliable thermodynamic parameters of complexation are of great importance. The thermodynamic parameters of complexation can be determined by various complementary methods, which increases the reliability of results. The thermodynamic parameters of the reaction of formation of a silver(I) monocomplex with 1-methyl-2-mercaptoimidazole (logK°, ∆_rG°, ∆_rH°, ∆_rS°) were determined by isothermal titration calorimetry in water at T = 298.15 K. The results were compared with the thermodynamic parameters obtained previously by potentiometric titration using the temperature coefficient method to determine the enthalpy of complexation.

Vapor–liquid surface tension is calculated on the evaporation curve of n-nonane in the SAFT-γ Mie model. The calculations are made via molecular dynamics for temperatures in the range of 410 to 505 K. The effect the cutoff radius of the interparticle interaction potential in the model has on the coefficient of surface tension and the difference between densities of the liquid and vapor phases is studied. An extrapolation algorithm is proposed for estimating surface tension with an uncut potential of interaction. The results are in good agreement with tabular values of surface tension. Extrapolation allows the systematic error of calculations to be estimated, while reducing the computational complexity relative to the direct modeling of a system with a large potential cutoff radius.

Criteria for selecting the best antisolvent among aliphatic amines: dipropylamine, diisopropylamine, and triethylamine were developed. The phase behavior of 14 salt–water–amine ternary systems was analyzed, including salts with different solubilities and salting-out abilities (sodium and potassium formats; sodium, potassium, and cesium nitrates; lithium and sodium chlorides; potassium bromide and iodide). The temperature dependences of the composition of the critical solution were determined for the majority of systems, and isothermal phase diagrams were constructed for all of them. The compositions of the equilibrium phases of the monotectic state were used to calculate the yield of salt crystals depending on the antisolvent concentration and temperature. The optimum conditions for the process can be determined based on the analysis of the phase diagrams of systems in a certain temperature range. The revealed tendencies in extractive crystallization made it possible to significantly reduce the amount of experimental work to find the best conditions for extracting the salts from aqueous solutions and to propose a research algorithm. The algorithm makes it possible to reduce the experiment by 6–8 times and to carry out an express assessment of the effectiveness of an antisolvent for a particular salt without phase selection and their chemical analysis.

The authors investigate the solubility curves of nematic phenyl benzoates (p-hexyloxyphenyl esters of p-alkyloxybenzoic acids, n-alkyl = n-butyl and n-heptyl) in organic solvents of various kinds (n-hexane, n‑heptane, methanol, ethanol, 1-propanol, 2-propanol, 1,4-dioxane, diethyl ether, tert-butyl methyl ether, and ethyl acetate). The solubility of phenylbenzoates were estimated using the parameters of solubility. A scheme was proposed for estimating the enthalpy of vaporization, molar volume, and Hildebrand solubility parameter of aromatic esters of benzoic acid at 298.15 K.