We present a corresponding states correlation based on the description of fluid phase properties by means of an Mie intermolecular potential applied to tangentially bonded spheres. The macroscopic properties of this model fluid are very accurately represented by a recently proposed version of the Statistical Associating Fluid Theory (the SAFT-γ version). The Mie potential can be expressed in a conformal manner in terms of three parameters that relate to a length scale, σ, an energy scale, ε, and the range or functional form of the potential, λ, while the nonsphericity or elongation of a molecule can be appropriately described by the chain length, m. For a given chain length, correlations are given to scale the SAFT equation of state in terms of three experimental parameters: the acentric factor, the critical temperature, and the saturated liquid density at a reduced temperature of 0.7. The molecular nature of the equation of state is exploited to make a direct link between the macroscopic thermodynamic parameters used to characterize the equation of state and the parameters of the underlying Mie potential. This direct link between macroscopic properties and molecular parameters is the basis to propose a top-down method to parametrize force fields that can be used in the coarse grained molecular modeling (Monte Carlo or molecular dynamics) of fluids. The resulting correlation is of quantitative accuracy and examples of the prediction of simulations of vapor−liquid equilibria and interfacial tensions are given. In essence, we present a recipe that allows one to obtain intermolecular potentials for use in the molecular simulation of simple and chain fluids from macroscopic experimentally determined constants, namely the acentric factor, the critical temperature, and a value of the liquid density at a reduced temperature of 0.7.

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We report surface tension measurements, coexisting densities, concentration profiles along the interfacial region, surface activities, and relative Gibbs adsorption isotherms for binary mixtures of carbon dioxide (CO 2 ) + n-decane (n-C 10 H 22 ) at 344.15 K and carbon dioxide (CO 2 ) + n-eicosane (n-C 20 H 42 ) at 323.15 K over a pressure range from 0.1 MPa to 10.35 MPa. The results are obtained by employing a broad approach that integrates experiments with both theory and molecular simulations to gain an enhanced multiscale description of the interfacial region. Measurements are based on the use of a high-pressure pendant drop tensiometer coupled to a high-pressure densimeter. Theoretical modeling is carried out using the Square Gradient Theory based on a version of the Statistical Associated Fluid Theory (SAFT-VR Mie) equation of state. At the molecular level, Molecular Dynamics is employed and molecules are represented by the SAFTγ coarse-grained force field. The novelty here is that both the theory and the simulations uniquely share the same underlying intermolecular potentials, hence the experimental data are employed to verify and inform in the same way both the theory and simulations. Reassuringly, theory, experiments, and molecular simulations agree with each other in the description of the bulk phase equilibria and interfacial tension. It is observed that for both mixtures, the interfacial tension decreases as the pressure (or the liquid mole fraction of CO 2 ) increases. Furthermore, there is quantitative agreement between the theoretical predictions and the results obtained from the molecular simulations of surface activities, concentration profiles along the interfacial region, and relative Gibbs adsorption isotherms at the interfaces. A remarkable high excess adsorption of CO 2 , larger in eicosane than in decane, is detected along the interface.

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The accurate description of the phase equilibria and interfacial behavior of the ternary mixture H2O + CO2 + CH4 is of fundamental importance in processes related with enhanced natural gas recovery, CO2 storage, and gas-oil miscibility analysis. For this reason, the physical understanding and theoretical modeling of this remarkably complex mixture, in a wide range of thermodynamic conditions, constitutes a challenging task both for scientists and engineers. This work focuses on the description of the interfacial behavior of this mixture, with special emphasis on several regions that yield different scenarios (vapor–liquid, liquid–liquid, and vapor–liquid–liquid equilibria) and in pressure and temperature ranges related with the practical applications previously mentioned. A comparison between three alternative approaches has been performed: atomistic Monte Carlo simulations (MC), coarse grained molecular dynamics (CG-MD) simulations, and density gradient theory (DGT) have been used to characterize the interfacial region, describing in detail complex phenomena, including preferential adsorption and wetting phenomena even in the ternary triphasic region. Agreement between the results obtained from different methods indicate that the three alternative approaches are fully equivalent to analyze the interfacial behavior. It has been also found that the preferential adsorption of CO2 over H2O interface is greater if compared to CH4 in all conditions characterized. In fact, we have also demonstrated that CH4 under triphasic conditions has very limited influence on the complete wetting of the binary system H2O + CO2.

Molecular dynamics simulations are conducted to investigate the initial stages of spontaneous imbibition of water in slit silica nanochannels surrounded by air. An analysis is performed for the effects of nanoscopic confinement, initial conditions of liquid uptake and air pressurization on the dynamics of capillary filling. The results indicate that the nanoscale imbibition process is divided into three main flow regimes: an initial regime where the capillary force is balanced only by the inertial drag and characterized by a constant velocity and a plug flow profile. In this regime, the meniscus formation process plays a central role in the imbibition rate. Thereafter, a transitional regime takes place, in which, the force balance has significant contributions from both inertia and viscous friction. Subsequently, a regime wherein viscous forces dominate the capillary force balance is attained. Flow velocity profiles identify the passage from an inviscid flow to a developing Poiseuille flow. Gas density profiles ahead of the capillary front indicate a transient accumulation of air on the advancing meniscus. Furthermore, slower capillary filling rates computed for higher air pressures reveal a significant retarding effect of the gas displaced by the advancing meniscus.