Thermodynamic analysis of oligomeric blends by applying the Kirkwood-Buff theory of solutions

The accurate prediction of the thermodynamic properties of oligomeric blends and, in general, binary liquid mixtures from atomistic simulations is a challenging task. In this work we develop a methodology for the full thermodynamic analysis of oligomeric blends and the extraction of the Flory-Huggins interaction parameter from the Gibbs energy of mixing, combining Flory-Huggins thermodynamics with Kirkwood-Buff theory of solutions. We perform a series of Molecular Dynamics (MD) simulations of 2-methylpentane/n-heptane mixtures, at various mole fractions. Firstly we validate the forcefield we apply in our MD simulations, comparing the density and excess volume we obtain against the corresponding experimental estimates found in the literature. Then we calculate the Kirkwood-Buff integrals in the isothermal-isobaric (NpT) ensemble, applying the particle fluctuations method, and we extract the component activity coefficients, the excess Gibbs energy, the excess enthalpy, and the excess entropy of mixing as functions of the mole fraction. Finally we calculate the Flory-Huggins interaction parameter χ by interpreting the Gibbs energy of mixing in the framework of Flory-Huggins theory, and explore its dependence on composition. All results are compared against experimental measurements in order to evaluate our methodology. Agreement is found to be very good.

Thermodynamic Assessment of the AF–CrF3 (A = Li, Na, K) and CrF2–CrF3 Systems

Understanding the corrosion mechanisms and the effect of corrosion products on the basic properties of the salt (e.g., melting point, heat capacity) is fundamental for the safety assessment and durability of molten salt reactor technology. This work focused on the thermodynamic assessment of the CrF2−CrF3 system and the binary systems of chromium trifluoride CrF3 with alkali fluorides (LiF, NaF, KF) using the CALPHAD (computer coupling of phase diagrams and thermochemistry) method. In this work, the modified quasi-chemical model in the quadruplet approximation was used to develop new thermodynamic modelling assessments of the binary solutions, which are highly relevant in assessing the corrosion process in molten salt reactors. The agreement between these assessments and the phase equilibrium data available in the literature is generally good. The excess properties (mixing enthalpies, entropies and Gibbs energies) calculated in this work are consistent with the expected behaviour of decreasing enthalpy and Gibbs energy of mixing with the increasing ionic radius of the alkali cations.

Modelling thermodynamic properties of binary Cu–Eu and ternary Al–Cu–Eu melts

Model calculations of the whole set of thermodynamic properties of liquid alloys for the binary Cu–Eu and ternary Al–Cu–Eu systems have been performed. Authors used the ideal associated solution model (IAS model) for calculation of the entropies and excess Gibbs energies of mixing for these systems. The binaries were given as the Redlich-Kister polynomials. The thermodynamic properties for the ternary system are described using the Redlich-Kister-Muggianu formalism. A comparison of the surfaces of excess Gibbs energy and entropy of mixing for liquid Al–Cu–Eu alloys at 1350 K demonstrates that the ordering related to the formation of rather strong associates in the Al–Eu system significantly affects the concentration dependence of the excess Gibbs energy of mixing in the liquid phase at this temperature.

Activity Coefficient of Different Salt Solutions for Reverse Electrodialysis Application

Renewable energy sources and related conversion technologies are considered as the main solution for resolving the current issues related to global warming and environmental protection. Salinity gradient energy (SGE) is a source of renewable energy which can be defined as the Gibbs Energy of mixing when two solutions with different salinities mix together. The difference in the salinity of salt solutions is the main driving force of energy production by the SGE conversion technologies. One of the main conversion technologies of SGE is reverse electrodialysis (RED). In this technology the gradient between the concentrated and diluted salt solutions, the ions with a negative charge (anion) and positive charge (cation) pass through selective ion exchange membranes known as anion exchange membrane and cation exchange membrane. The driving force for diffusion of the ions is a function of the concentration gradient. The chemical potential of the salt solution is a function of the concentration of the salt solution and plays an important role in the Gibbs energy of mixing. The chemical potential of the salt solution is a thermodynamic property which is a function of the concentration and activity coefficient of the salt solution. The activity coefficient of the salt solution is a unique parameter which depends on the ionic strength of the solution and the type of ions in the salt solution. The salts with higher activity coefficient have a higher potential to be used in the SGE conversion process due to higher released Gibbs Energy during the mixing process. In this paper the thermodynamic model presented by Bromley [1], is used to calculate activity coefficient of 20 salts at different concentrations (0.01–6 molal). Two dimensionless parameters, Φ and Ψ, are defined as the ratio of activity coefficient and concentration between the concentrated and diluted solutions in 6 and 0.5 molal respectively. Using the dimensionless parameters, the theoretical open circuit voltage (OCV) of salt solutions in a RED cell is calculated. The salts are screened and ranked based on the activity coefficients and the theoretical open circuit voltage (OCV). The best salts are selected for use in a RED cell based on the activity coefficients and theoretical OCV. These alts could have potential for developing SGE storage systems in combination with renewable energy devices.

Triphase Separation of a Ternary Symmetric Highly Viscous Mixture

We discuss numerical results of diffusion-driven separation into three phases of a symmetric, three-component highly viscous liquid mixture after an instantaneous quench from the one-phase region into an unstable location within the tie triangle of its phase diagram. Our theoretical approach follows a diffuse-interface model of partially miscible ternary liquid mixtures that incorporates the one-parameter Margules correlation as a submodel for the enthalpic (so-called excess) component of the Gibbs energy of mixing, while its nonlocal part is represented based on a square-gradient (Cahn–Hilliard-type) modeling assumption. The governing equations for this phase-field ternary mixture model are simulated in 3D, showing the segregation kinetics in terms of basic segregation statistics, such as the integral scale of the pair-correlation function and the separation depth for each component. Based on the temporal evolution of the integral scales, phase separation takes place via the simultaneous growth of three phases up until a symmetry-breaking event after which one component continues to separate quickly, while phase separation for the other two seems to be delayed. However, inspection of the separation depths reveals that there can be no symmetry among the three components at any instant in time during a triphase segregation process.

Stability Analysis of Binary Solvent Mixtures for Herbal Phytochemical Extraction

Most of the extraction processes of herbal phytochemicals use solvent mixtures as a phytochemical transfer mediums. It is very important to predict the stability of solvent mixtures before it is used to extract herbal phytochemicals. In order to prevent any disturbance in the herbal extraction, the solvent mixtures must be in a single liquid phase (miscible to each other). In this study, the stabilities of five binary solvents (methanol-water, methanol-ethyl acetate, methanol-acetic acid, methanol-n-propionaldehyde, and methanol-isobutyraldehyde mixtures) that could be used in the current extraction processes are evaluated. The main purpose of this study is to evaluate these binary solvents in terms of their stability using Gibbs energy of mixing. The value of the function ?Gmix/RT is calculated for each solvent mixture. Then, the graph for ?Gmix/RT versus solvent molar fraction x is plotted. From this plot and the value of function ?Gmix/RT, it can be concluded whether the solvent mixtures are stable or unstable. From the analysis, all five binary mixtures are stable within the selected molar fraction making all mixtures are suitable to be applied in herbal extraction.