Prediction of the water/oil interfacial tension from molecular simulations using the coarse-grained SAFT-γ Mie force field

Abstract

This work is framed within the Ninth Industrial Fluid Properties Simulation Challenge, with the aim of assessing the capability of molecular simulation methods and force fields to accurately predict the interfacial tension of oil + water mixtures at high temperatures and pressures. The challenge focused on predicting the liquid-liquid interfacial tension of binary mixtures of dodecane + water, toluene + water and a 50:50 (wt%) mixture of dodecane:toluene + water at 1.825 MPa (250 psig) and temperatures from 110 to 170 °C. In our entry for the challenge, we employed coarse-grained intermolecular models parametrized via a top-down technique in which an accurate equation of state is used to link experimentally observed macroscopic properties of fluids with the force-field parameters. The state-of-the-art version of the statistical associating fluid theory (SAFT) for potentials of variable range as reformulated in terms of the Mie potential is employed here. Interfacial tensions are calculated through a direct method, where an elongated simulation cell is sampled through molecular dynamics in the isobaric-isothermal constant area ensemble (NP zz AT). The coarse-grained nature of the force field allows for the accelerated calculation of relatively large systems. The binary interaction parameters that describe the crossinteractions have been obtained in previous works by fitting to interfacial tensions of the constituent binaries at lower pressures and temperatures; these are taken as constant for all conditions and mixtures studied. After disclosure of the challenge results, we observe that the interfacial properties of the mixtures are described with an error of less than 5 mN/m over the whole range of conditions, demonstrating the accuracy and transferability of the top-down SAFT-γ Mie force field approach.

A kinetic description of how interfaces accelerate reactions in micro-compartments

“…A thickness of 1 nm is used and is consistent with Molecular Dynamics simulations of the density prole across an oil/water interface. 42 Bulk and surface concentrations Fig. 2.…”

Surrogate Models for Studying the Wettability of Nanoscale Natural Rough Surfaces Using Molecular Dynamics

“…This connection facilitates the direct estimation of effective force field parameters by fitting the resulting equation of state to a wide a range of thermophysical properties without the need to perform extensive simulations. To date, the SAFT force field has been used successfully in the prediction of the behavior of crude oils in bulk [81,82] and confined reservoirs [83], high pressure oil/water interfacial tensions [84], adsorption [85], and the wetting behavior of surfactant solutions on surfaces [56,86], amongst others.…”

Molecular Dynamics Simulation of the Superspreading of Surfactant-Laden Droplets. A Review

“…In practice, the EoS offers an accurate fit for the force-field parameters, where the key nonbonded interactions are expressed by means of the Mie potential (Equation (6)). The macroscopically observed thermophysical properties that stem from the fluid-fluid and fluid-solid interactions are well reproduced by the model, which is a direct consequence of the close match between the theory and the underlying Hamiltonian of the system [65][66][67]95,101,[106][107][108][109]. The SAFT approach derives robust and transferable potentials of effective beads that represent groups of atoms as in the case of the MARTINI model.…”