Molecular dynamics simulations of the role of salinity and temperature on the hydrocarbon/water interfacial tension

Interfacial tension of some hydrocarbon/water systems, including a mixture of aliphatic and aromatic hydrocarbons, has been estimated on the basis of molecular dynamics simulations. The dependence of the interfacial properties on the salinity of the aqueous phase and the temperature has been simulated. Different concentrations in NaCl and CaCl2 up to 2 M have been used. It is found that, in all considered cases, interfacial tension increases with salt concentration. This effect depends on the preference of the salt ions for the bulk of the aqueous phase that, in turn, results in an increased difficulty for the water molecules to be at the interface. The influence of salinity is fundamentally electrostatic in origin and does not depend on the chemical nature of the salt cation. Finally, the impact of temperature on the dodecane/brine interfacial tension has also been inspected. A decreasing of the values of the interfacial tension is found in agreement, both in trend and magnitude, with experimental available data.