Free Energy Of Dissolution Research Articles

Exploring detailed microcosmic mechanisms of sodium chloride deposition in supercritical water reactors from the aspect of solvation structure: A combination of MD and QM simulations

The dissolution characteristics and microscopic dissolution process of salt in supercritical water (SCW) are the fundamental influence of scale formation. In this paper, molecular dynamics (MD) and quantum mechanics (QM) were used to study the solubility and solvation structure of sodium chloride in supercritical water. The potential mean force (PMF), radial distribution function (RDF) and coordination number (CN) indicate that the solubility of sodium chloride in SCW decreases with the increase of temperature and the decrease of density. As the system density decreases from 0.3 g/cm3 to 0.1 g/cm3 and the temperature increases from 600 K to 900 K, the CN of water molecules in the solvation shell decreases from 2.89 to 1.01, which is consistent with the trend of the experimental results. The electrostatic potential distribution and intermolecular interaction of the solvation shell around Na+ were obtained by QM method. The solution free energy of Na+–3H2O in implicit solvent was obtained. In the condition range of this study, when the temperature is the lowest and the dielectric constant is the largest, the free energy of dissolution is the smallest, which is −0.0991 a.u. This study will lay a foundation for the study of salt deposition in SCW.

Qualitative and quantitative study of intermolecular weak interactions for aminosalicylic acid isomers by terahertz spectroscopy

AbstractIn the field of chemical science, the development of new drugs, the formation of crystals and molecular clusters, and the optimization of drug safety and efficacy are all closely related to weak molecular interactions. In this paper, the salicylic drugs 4‐aminosalicylic acid (4‐ASA) and 5‐aminosalicylic acid (5‐ASA) are used as the research objects. First, the terahertz (THz) absorption spectra of the two isomers were measured in the range of .4–2.0 THz by terahertz time‐domain spectroscopy (THz‐TDS). Then the unit cells were calculated by using density functional theory (DFT). We found that the characteristic absorption peaks of the experimental spectra were basically consistent with the theoretical calculation. In addition, under the solvent model, the free energy of dissolution and the free energy of the systems were considered and calculated, and the results showed that solvation had a certain influence on the position and intensity of spectral absorption peaks. In order to further explore the origin of the characteristic absorption peaks, the vibrational properties of the unit cell model were analyzed using the potential energy distribution (PED) method. At the same time, the weak interactions of the system were qualitatively and quantitatively analyzed by interaction region indicator (IRI) and energy decomposition analysis based on forcefield (EDA‐FF) methods, respectively. The results show that the absorption peaks of 4‐ASA and 5‐ASA are mainly derived from the vibration mode of dihedral angle torsion. The weak interactions in the 4‐ASA are dominated by dispersion, while they are dominated by electrostatic and dispersion in the 5‐ASA. Therefore, it is an effective way to identify isomers and study intermolecular weak interactions by using THz‐TDS combined with PED, IRI, and EDA‐FF.

Solubility and solution thermodynamics of 2, 6-bis (4-hydroybenzylidene) cyclohexanone in pure and binary solvents at various temperatures

Solubility of 2, 6-bis (4-hydroxybenzylidene) cyclohexanone (BHBC) in pure solvents such as 1,4-dioxane, methanol, 1-butanol, 1-propanol, ethyl acetate, acetone, tetrahydrofuran (THF), glacial acetic acid, dimethyl sulphoxide (DMSO) and binary solvents dimethyl formamide (DMF) and (1-Propanol + Tetrahydrofuran) were investigated by gravimetric method at different temperature range. The experiment solubility increases with increase in temperature in both pure and binary solvents. The Maximum solubility is found in DMF at 328.15 K and for binary solvent mixture i.e. 1-propanol and THF (0.9 mol fraction) it was maximum at 318.15 K. Further modified Apelblate and Buchowski-Ksiazczak models were used for the theoretical calculation of solubility of BHBC in pure as well binary solvents. A satisfactory correlation of these models with experimental data was observed. The solution thermodynamics parameters like enthalpies, Gibb's free energy of dissolution and entropy of solutions were calculated using Van't Hoff and Gibb's equation, which reveals the solvation mechanism is non-spontaneous and entropy driven.

Liquid state properties of SEI components in dimethoxyethane

The solid-electrolyte interphase (SEI) layer is a critical constituent of battery technology, which incorporates the use of lithium metals. Since the formation of the SEI is difficult to avoid, the engineering and harnessing of the SEI are absolutely critical to advancing energy storage. One problem is that much fundamental information about SEI properties is lacking due to the difficulty in probing a chemically complex interfacial system. One such property that is currently unknown is the dissolution of the SEI. This process can have significant effects on the stability of the SEI, which is critical to battery performance but is difficult to probe experimentally. Here, we report the use of ab initio computational chemistry simulations to probe the solution state properties of SEI components LiF, Li2O, LiOH, and Li2CO3 in order to study their dissolution and other solution-based characteristics. Ab initio molecular dynamics was used to study the solvation structures of the SEI with a combination of radial distribution functions, discrete solvation structure maps, and vibrational density of states, which allows for the determination of free energies. From the change in free energy of dissolution, we determined that LiOH is the most likely component to dissolve in the electrolyte followed by LiF, Li2CO3, and Li2O although none were favored thermodynamically. This indicates that dissolution is not probable, but Li2O would make the most stable SEI with regard to dissolution in the electrolyte.

A New Method to Determine the Half-Life for Penicillin Using Microcalorimeter

The dissolution process of penicillin in normal saline and isotonic glucose solution was reported using a microcalorimeter. Both the integral and differential heats of solution were measured. The quantitative relationships between the amount of heat released and the quantity of dissolved penicillin were established. Meanwhile, the kinetics and the half-life of the dissolution processes as well as the enthalpy of solution, the entropy of dissolution, and the free energy of dissolution were determined. The results showed that a change of the solvent from normal saline to isotonic glucose solution had little effect on the half-life of penicillin in the dissolution process, and there was no significant difference between the stabilities of penicillin in isotonic glucose solution and normal saline. Moreover, the dissolution process of penicillin in isotonic glucose solution followed the first-order kinetics. These results could provide a theoretical basis for the clinical applications of penicillin.

Effect of Polyoxyethylene Type Nonionic Surfactant and Polar Lipophilic Oil on Solubilization of Mixed Surfactant Microemulsion Systems

In the present report, the water solubilization capacity of water-in-oil microemulsion systems comprising mixed surfactants, that is, anionic sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and nonionic(s) [viz., polyoxyethylene (2) stearyl ether (Brij-72), polyoxyethylene (10) stearyl ether (Brij-76), polyoxyethylene (20) stearyl ether (Brij-78), polyoxyethylene (2) oleyl ether (Brij-92), polyoxyethylene (10) oleyl ether (Brij-97), and polyoxyethylene (20) oleyl ether (Brij-98)] was investigated in polar lipophilic oils [viz., ethyl myristate (EM), isopropyl myristate (IPM), and isopropyl palmitate (IPP)] with varying mole fractions of nonionic surfactant (Xnonionic) at a fixed surfactant concentration and 303 K. A maximum (i.e., synergism) in water solubilization (ω0,max) was observed at an optimal value of mole fraction of nonionic surfactant (Xnonionic,max). The solubilization efficiency parameter (SP*water) and the free energy of dissolution (ΔG0s) were evaluated for these mixed systems. All of the physicochemical parameters for solubilization (viz., ω0,max, Xnonionic,max, and SP*water) were found to be dependent on both nonionic surfactants and oils. A minimum in ΔG0s was observed at corresponding Xnonionic,max, where a maximum in SP*water was evidenced. The IPP-based system was found to be most efficient, whereas the EM-based system was least efficient. An attempt was made to correlate the interdependence of physicochemical (ω0,max or SP*water) and thermodynamic (ΔG0s) parameters.

Atomistic simulation of the free energies of dissolution of ions from flat and stepped calcite surfaces

Molecular dynamics simulations were used to describe the interaction of calcite flat and stepped surfaces with water. The calculations show that the disruptions of the water density caused by the presence of monoatomic step extend further in the direction normal to the surface than in the direction normal to the step edge. When vacancies were introduced, the disruption of the water density was dependent on both the type of vacancy and step. By performing a series of molecular dynamics simulations we were able to obtain free energy profiles of the dissolution of ions from flat and stepped surfaces. These results show that the type of surface that the ion is being dissolved from has a profound effect on the free energy of dissolution. In addition, our calculations suggest that the relationship between the overall free energy of dissolution and the number of crystal bonds to be broken is not linear, as normally assumed in dissolution models such as the solid-on-solid model.

Computer simulation of the effect of salt on the hydrophobic effect

Molecular dynamics simulations of aqueous solutions containing methane and sodium chloride reveal the existence of a structured hydration shell around the non-polar solutes, although this hydration shell is less well defined than in the case where salt is absent. It was also observed that hydrogen bonds made from the hydration shell across to the bulk are weaker than those in the bulk, with or without salt. Although the geometry of the hydrogen bonds is preserved, there is a larger fraction of broken hydrogen bonds in the hydration shell of the non-polar solutes than in the bulk of the solution, the difference increasing with increasing temperature. The number of broken H bonds is significantly larger in the presence of salt, and should contribute to an increase in the free energy of dissolution and hence to a lowering of the solubility and an increase in the hydrophobic interaction.

Use of AES to Determine Low Solubilities of Impurities: Case of MnS in Austenitic Stainless Steel

The solubility of manganese sulfide in a commercial 304 austenitic stainless steel was studied using AES to determine surface sulfur segregation. The segregation mechanism at stainless steel surfaces were extensively studied, but thermodynamic data such as segregation free energy, or manganese sulfide dissolution heat have not been established, although these data are of great interest because the MnS dissolution parameters give the amount of free sulfur in solid solution. The only solubility data for manganese sulfide in austenitic steel was given to Turkdogan in 1955 and concerned MnS in iron-manganese alloys. In the present study, the Auger spectra are used to calculate the free energy of dissolution of manganese sulfide as well as the sulfur segregation parameters in austenitic stainless steel.

Thermodynamics of Nickel Aluminate Formation in Molten Nickel

AbstractAs part of an ongoing program of the study of oxidation and deoxidation reactions in nickel alloy melts, experiments were performed to determine the oxygen solubility in molten nickel in equilibrium with alumina and nickel aluminate in the temperature range 1733–1873 K. Experiments were conducted at the University of Toronto with nickel of initial low oxygen content while those at the University of Kyoto were with initial high oxygen content. The results show very good agreement. Both sets of results were combined to show the effect of temperature on the reaction under investigation as follows:Ni(l)+O +Al2O3(s) = NiO. Al2O3(s);∆G0=(−188,840±16,700)+(82.8±9.3)T J mol−1.The oxygen potential of the melt corresponding to the three phase equilibrium was measured by means of a disposable oxygen probe and the results were utilized to redetermine the free energy of dissolution of oxygen gas in liquid nickel in the temperature range 1733–1873 K, which is given as:1/2 O2(g) = O(Ni)(1 wt%), ∆G0 = −102,420+19...

On the problem of empirical characteristics of a medium and their mutual relations

New parameters of polarity, acidity, and basicity of a medium, which are more suitable to characterize nonspectral solvent effects, were derived by dividing the Taft-Kamlet solvent parameters π*, α, and β by a function of the refractive index n, f(n) = (n2 - 1)/(2n2 + 1). The new parameters were used in evaluating the effect of the medium on reaction rates, equilibria, solubilities, hyperfine splitting constants in EPR spectra, fluorescence life time, free energy of dissolution of ions and ion pairs, and on the Snyder solvent factors of the elution strength in chromatography.

A general method of classifying stationary phases and estimating their polarity and selectivity on the basis of thermodynamic characteristics

1. Empirical equations used for classifying stationary phases in terms of differences in retention indices have been developed. It has been shown that the energy equivalent of the index unit varies from one phase to the other. 2. A system is described by means of which one can estimate the polarities of stationary phases and adsorbents from the differential molar free energies of dissolution of n-alkane methyl groups and five test compounds. 3. A thermodynamic criterion for the selection of a comparison phase in selectivity determinations has been set up. 4. A quantitative method for estimating stationary-phase selectivities from differences in the excess free energy of mixing has been described.

Free energy of adsorption of some organic additives as a function of the molar free energy of dissolution

Free energy of adsorption of some organic additives as a function of the molar free energy of dissolution

Free energy of adsorption of some organic additives as a function of the molar free energy of dissolution

Free energy of adsorption of some organic additives as a function of the molar free energy of dissolution