Quantitative predictions of interfacial tension for ternary liquid-liquid systems using dissipative particle dynamics

The liquid-liquid interfacial tension (IFT) is a key property for many industrial applications such as liquid-liquid extraction or chemical Enhanced Oil Recovery (EOR). Among theoretical methods for estimating the interfacial... [ view full abstract ]

The liquid-liquid interfacial tension (IFT) is a key property for many industrial applications such as liquid-liquid extraction or chemical Enhanced Oil Recovery (EOR). Among theoretical methods for estimating the interfacial tension, molecular simulation appears as the most advantageous. To simulate large and complex systems, the Dissipative Particle Dynamics (DPD) method, based on a coarse-grained model in order to reduce the number of degrees of freedom and therefore the computational time, seems to be the most appropriate approach. Intermolecular interactions between two beads are modeled by soft repulsions in the conservative force. However, the parametrization of intermolecular interactions for quantitative predictions of IFT for multi-component systems is still challenging.

In this communication, a methodology based on DPD simulations to provide quantitative variation of IFT for ternary liquid-liquid systems as a function of the solute concentration is proposed. A key step of the parametrization method proposed here is the use of Flory-Huggins Gibbs free energy between the DPD beads. Parametrization is carried out in order to reproduce the liquid-liquid phase diagram using experimental compositional data. This methodology has been used on several systems such as water/1,4-dioxane/benzene, water/acetone/chloroform and water/acetic acid/benzene. Gibbs (NVT) ensemble Coarse Grained-Monte Carlo (CG-MC) simulations have been used to compute the solubility of the solute in each phase. The precise bulk phase compositions in the heterogeneous systems (prior to IFT calculations) were computed using CG-MC osmotic (N_solventP_zzµ_soluteT) ensemble. This step allows a perfect comparison with experimental data. Finally, DPD simulations were used to predict accurate IFT values for different solute concentrations. Furthermore, this approach allows us to determine the solute composition at the interface area. These data are significant for many applications since it makes possible to compare the activity of different compounds at the interface. For example, DPD simulations can be used to select the most efficient surfactants for the water/oil interface for chemical EOR.

A procedure for the parametrization of interactions between DPD beads was proposed in this work for monofunctional molecules. Work is now in progress to adapt this approach for multifunctional molecules using the principle of parameter transferability. The strategy consists in treating each functional group individually on a ternary system to determine interaction parameters, then, to reuse them with the multifunctional molecules in multi-component systems.