Orientational order of the water molecules at the vicinity of the water–benzene interface in a broad range of thermodynamic states, as seen from Monte Carlo simulations

Abstract

Monte Carlo simulation of the water/benzene liquid–liquid interfacial system has been performed at six different thermodynamic state points, ranging from ambient conditions up to the vicinity of the critical point of water. The system has been found to consist of two immiscible liquid phases at every state point studied. The orientational preferences of the interfacial water molecules have been analysed in detail using the simulated configurations. The results obtained at ambient conditions are in agreement with previous results on various different water/apolar interfaces. Thus, interfacial water molecules have been found to have dual orientational preferences: the molecules located nearest to the organic phase prefer to stay perpendicular to the interface, pointing flatly toward the apolar phase by their dipole vectors, whereas the waters located somewhat farther from the organic phase prefer the parallel alignment with the interface. The observed orientational preferences are found to be rather stable with changing thermodynamic conditions: although the increase of the temperature has led, due to the increasing thermal motion of the molecules, to a gradual weakening of the orientational preferences, both preferences are found to exist up to at least 450 K, and found to be completely washed out at 575 K only. The pressure has not been found to influence the orientation of the water molecules noticeably.