Interfacial tension behaviour of water/hydrocarbon liquid-liquid interfaces: A molecular dynamics simulation

Molecular dynamics simulations of the water-isooctane interface are performed to sort out the effect of temperature on the properties of liquid-liquid interfaces. Reliable interaction potential models are applied to describe the interactions, including the treatment of long-range electrostatic forces. It is shown that the increase in temperature has little effect on the basic structural features of the interface, i.e. its sharpness and corrugation. Other interfacial properties, such as the density profile, specific solvent orientations or hydrogen-bonding characteristics are nearly identical for the range of temperatures considered (from 277 to 323 K). However, the liquid-liquid interfacial tension of the water/isooctane system has a non-monotonic behaviour, presenting a maximum at a specific temperature, in contrast to the monotonic decay found for the liquid-vapour case. This behaviour is similar to the one observed for binary mixtures of partially miscible Lennard-Jones fluids.