Simulation of the THF hydrate-water interfacial free energy from computer simulation.

In this work, the tetrahydrofuran (THF) hydrate-water interfacial free energy is determined at 500 bar, at one point of the univariant two-phase coexistence line of the THF hydrate, by molecular dynamics simulation. The mold integration-host methodology, an extension of the original mold integration technique to deal with hydrate-fluid interfaces, is used to calculate the interfacial energy. Water is described using the well-known TIP4P/Ice model, and THF is described using a rigid version of the TraPPE model.

Dissociation line and driving force for nucleation of the nitrogen hydrate from computer simulation. II. Effect of multiple occupancy.

In this work, we determine the dissociation line of the nitrogen (N2) hydrate by computer simulation using the TIP4P/Ice model for water and the TraPPE force field for N2. This work is the natural extension of Paper I, in which the dissociation temperature of the N2 hydrate has been obtained at 500, 1000, and 1500 bar [Algaba et al., J.

Prediction of the univariant two-phase coexistence line of the tetrahydrofuran hydrate from computer simulation.

In this work, the univariant two-phase coexistence line of the tetrahydrofuran (THF) hydrate is determined from 100 to 1000 bar by molecular dynamics simulations. This study is carried out by putting in contact a THF hydrate phase with a stoichiometric aqueous solution phase. Following the direct coexistence technique, the pressure is fixed, and the coexistence line is determined by analyzing if the hydrate phase grows or melts at different values of temperature.

Dissociation line and driving force for nucleation of the nitrogen hydrate from computer simulation.

In this work, we determine the dissociation line of the nitrogen (N2) hydrate by computer simulation using the TIP4P/Ice model for water and the TraPPE force field for N2. We use the solubility method proposed recently by some of us to evaluate the dissociation temperature of the hydrate at different pressures, from 500 to 1500 bar. Particularly, we calculate the solubility of N2 in the aqueous solution when it is in contact with a N2-rich liquid phase and when in contact with the hydrate phase via planar interfaces as functions of temperature.

Effect of pressure on the carbon dioxide hydrate-water interfacial free energy along its dissociation line.

We investigate the effect of pressure on the carbon dioxide (CO2) hydrate-water interfacial free energy along its dissociation line using advanced computer simulation techniques. In previous works, we have determined the interfacial energy of the hydrate at 400 bars using the TIP4P/Ice and TraPPE molecular models for water and CO2, respectively, in combination with two different extensions of the Mold Integration technique [J. Colloid Interface Sci.

Solubility of carbon dioxide in water: Some useful results for hydrate nucleation.

In this paper, the solubility of carbon dioxide (CO2) in water along the isobar of 400 bar is determined by computer simulations using the well-known TIP4P/Ice force field for water and the TraPPE model for CO2. In particular, the solubility of CO2 in water when in contact with the CO2 liquid phase and the solubility of CO2 in water when in contact with the hydrate have been determined. The solubility of CO2 in a liquid-liquid system decreases as the temperature increases.

Solubility of Methane in Water: Some Useful Results for Hydrate Nucleation.

In this paper, the solubility of methane in water along the 400 bar isobar is determined by computer simulations using the TIP4P/Ice force field for water and a simple LJ model for methane. In particular, the solubility of methane in water when in contact with the gas phase and the solubility of methane in water when in contact with the hydrate has been determined. The solubility of methane in a gas-liquid system decreases as temperature increases.

Simulation of the CO hydrate-water interfacial energy: The mold integration-guest methodology.

The growth pattern and nucleation rate of carbon dioxide hydrate critically depend on the precise value of the hydrate-water interfacial free energy. There exist in the literature only two independent experimental measurements of this thermodynamic magnitude: one obtained by Uchida et al. [J.

Density functional theory for the prediction of interfacial properties of molecular fluids within the SAFT-γ coarse-grained approach.

Recently, we have proposed the SAFT-VR Mie MF DFT approach [Algaba , , 2019, , 11937-11948] to investigate systems that exhibit fluid-fluid interfaces. This formalism is based on the combination of the Statistical Associating Fluid Theory for attractive potentials of variable range using Mie intermolecular potential (SAFT-VR Mie) and a Density Functional Theory (DFT) treatment of the free energy. A mean-field approach is used to evaluate the attractive term, neglecting the pair correlations associated to attractions.

Simulation of the carbon dioxide hydrate-water interfacial energy.

Hypothesis: Carbon dioxide hydrates are ice-like nonstoichiometric inclusion solid compounds with importance to global climate change, and gas transportation and storage. The thermodynamic and kinetic mechanisms that control carbon dioxide nucleation critically depend on hydrate-water interfacial free energy. Only two independent indirect experiments are available in the literature.

Molecular dynamics of liquid-liquid equilibrium and interfacial properties of aqueous solutions of methyl esters.

In this work, the liquid-liquid phase equilibria and interfacial properties of methyl ester + water binary mixtures are determined at atmospheric pressure and from 278 to 358 K combining the direct coexistence technique and molecular dynamics simulations. Methyl esters are modelled using new parametrizations based on the united atom TraPPE model force field proposed recently by us [E. Feria, J.

Molecular modelling techniques for predicting liquid-liquid interfacial properties of methanol plus alkane (-hexane, -heptane, -octane) mixtures.

In this work, the liquid-liquid interfacial properties of methanol plus n-alkane (n-hexane, n-heptane, n-octane) mixtures are investigated at atmospheric pressure by two complementary molecular modelling techniques; namely, molecular dynamic simulations (MD) and density gradient theory (DGT) coupled with the PC-SAFT (perturbed-chain statistical associating fluid theory) equation of state. Furthermore, two molecular models of methanol are used, which are based on a non-polarisable three site approach. On the one hand, is the original (flexible) TraPPE-UA model force field.

Preferential Orientations and Anomalous Interfacial Tensions in Aqueous Solutions of Alcohols.

Literature studies on interfacial tension versus temperature between normal alcohols and water show that it increases with temperature and exhibits a maximum value at a given temperature depending on the molecular weight of the alcohol. This very unusual behavior is supposedly accompanied by the formation of monolayers of alcohol molecules oriented preferentially at the interface, a structural issue not confirmed until now. We use molecular-based models for water and alcohols in combination with molecular dynamics simulations to provide physical insights, from a molecular perspective, into the structural and thermodynamic behavior at the liquid-liquid interfaces of aqueous solutions of alcohols.

Vapour-liquid phase equilibria and interfacial properties of fatty acid methyl esters from molecular dynamics simulations.

We have determined the phase equilibria and interfacial properties of a methyl ester homologous series (from methyl acetate to methyl heptanoate) using direct simulations of the vapour-liquid interfaces. The methyl esters are modelled using the united atom approach in combination with transferable parameters for phase equilibria (TraPPE) force fields for alkanes, alkenes, carbon dioxide, ethers, and carboxylic acids in a transferable way. This allows us to take into account explicitly both dispersive and coulombic interactions, as well as the repulsive Pauli-exclusion interactions.

An accurate density functional theory for the vapor-liquid interface of chain molecules based on the statistical associating fluid theory for potentials of variable range for Mie chainlike fluids.

A new Helmholtz free energy density functional is presented to predict the vapor-liquid interface of chainlike molecules. The functional is based on the last version of the statistical associating fluid theory for potentials of variable range for homogeneous Mie chainlike fluids (SAFT-VR Mie). Following the standard formalism, the density functional theory (SAFT-VR Mie DFT) is constructed using a perturbative approach in which the free energy density contains a reference term to describe all the short-range interactions treated at the local level, and a perturbative contribution to account for the attractive perturbation which incorporates the long-range dispersive interactions.

Vapour-liquid interfacial properties of square-well chains from density functional theory and Monte Carlo simulation.

The statistical associating fluid theory for attractive potentials of variable range (SAFT-VR) density functional theory (DFT) developed by [Gloor et al., J. Chem.

Understanding the interfacial behavior in isopycnic Lennard-Jones mixtures by computer simulations.

The physical characterization of the singular interfacial behavior of heterogeneous fluid systems is a very important step in preliminary stages of the design process, and also in the subsequent procedures for the determination of the optimal operating conditions. Molar isopycnicity or molar density inversion is a special case of phase equilibrium behavior that directly affects the relative position of phases in heterogeneous mixtures, without being affected by gravitational fields. This work is dedicated to characterize the impact of molar density inversion on the interfacial properties of Lennard-Jones binary mixtures.

Density functional theory for the description of spherical non-associating monomers in confined media using the SAFT-VR equation of state and weighted density approximations.

As a first step of an ongoing study of thermodynamic properties and adsorption of complex fluids in confined media, we present a new theoretical description for spherical monomers using the Statistical Associating Fluid Theory for potential of Variable Range (SAFT-VR) and a Non-Local Density Functional Theory (NLDFT) with Weighted Density Approximations (WDA). The well-known Modified Fundamental Measure Theory is used to describe the inhomogeneous hard-sphere contribution as a reference for the monomer and two WDA approaches are developed for the dispersive terms from the high-temperature Barker and Henderson perturbation expansion. The first approach extends the dispersive contributions using the scalar and vector weighted densities introduced in the Fundamental Measure Theory (FMT) and the second one uses a coarse-grained (CG) approach with a unique weighted density.

Monte Carlo simulation of flexible trimers: from square well chains to amphiphilic primitive models.

In this work, we present Monte Carlo computer simulation results of a primitive model of self-assembling system based on a flexible 3-mer chain interacting via square-well interactions. The effect of switching off the attractive interaction in an extreme sphere is analyzed, since the anisotropy in the molecular potential promotes self-organization. Before addressing studies on self-organization it is necessary to know the vapor liquid equilibrium of the system to avoid to confuse self-organization with phase separation.

Extension of the Test-Area methodology for calculating solid-fluid interfacial tensions in cylindrical geometry.

We extend the well-known Test-Area methodology of Gloor et al. [J. Chem.

Influence of the long-range corrections on the interfacial properties of molecular models using Monte Carlo simulation.

We analyze the influence of the long-range corrections, due to the dispersive term of the intermolecular potential energy, on the surface tension using direct simulation of the vapour-liquid interface of different molecular models. Although several calculation methods have been proposed recently to compute the fluid-fluid interfacial properties, the truncation of the intermolecular potential or the use of the tail corrections represents a contribution relevant from a quantitative perspective. In this work, a simplified model for methane, namely a spherical Lennard-Jones intermolecular potential, has been considered first, and afterwards other models including rigid non polarizable structures with both Lennard-Jones sites and point electric charges, representing some of the most popular models to describe water (namely the original TIP4P model, and the TIP4P/Ew and TIP4P/2005 versions), and carbon dioxide (MSM, EPM2, TraPPE, and ZD models) have been studied.

Semi-infinite boundary conditions for the simulation of interfaces: the Ar/CO2(s) model revisited.

We propose a method to account for the long tail corrections of dispersive forces in inhomogeneous systems. This method deals separately with the two interfaces that are usually present in a simulation setup, effectively establishing semi-infinite boundary conditions that are appropriate for the study of the interface between two infinite bulk phases. Using the wandering interface method, we calculate surface free energies of vapor-liquid, wall-liquid, and wall-vapor interfaces for a model of Lennard-Jones argon adsorbed on solid carbon dioxide.

Systems involving hydrogenated and fluorinated chains: volumetric properties of perfluoroalkanes and perfluoroalkylalkane surfactants.

As part of a combined experimental and theoretical study of the thermodynamic properties of perfluoroalkylalkanes (PFAAs), the liquid density of perfluorobutylpentane (F4H5), perfluorobutylhexane (F4H6), and perfluorobutyloctane (F4H8) was measured as a function of temperature from 278.15 to 353.15 K and from atmospheric pressure to 70 MPa.

Classical density functional theory for the prediction of the surface tension and interfacial properties of fluids mixtures of chain molecules based on the statistical associating fluid theory for potentials of variable range.

The statistical associating fluid theory for attractive potentials of variable range (SAFT-VR) density functional theory (DFT) developed by [G. J. Gloor et al.

Surface tension of fully flexible Lennard-Jones chains: role of long-range corrections.

We have calculated the interfacial properties of fully flexible chains formed from tangentially bonded Lennard-Jones beads by direct coexistence. The full long-range tails of the potential are accounted for by means of inhomogeneous long-range corrections consisting in slice by slice summation of interactions away from the truncation sphere. We show that the corrections may be transformed into an effective long-range pair potential plus a self term, thus allowing for a fast and easy implementation of the method.