Molecular Level Properties of the Water−Dichloromethane Liquid/Liquid Interface, as Seen from Molecular Dynamics Simulation and Identification of Truly Interfacial Molecules Analysis

The properties of the water−dichloromethane (DCM) liquid/liquid interface are investigated by molecular dynamics computer simulation. The results are analyzed in terms of the novel identification of truly interfacial molecules (ITIM) method. In this way, the molecules constituting the first molecular layer beneath the interface as well as those belonging to the consecutive molecular layers in both phases are identified, and the properties of interest are calculated separately for these separate molecular layers. The obtained results reveal that the influence of the interface on almost all properties of both phases disappears beyond the first molecular layer. Thus, the roughness of the first layer as well as the dynamics of the molecules belonging to this layer turn out to be considerably different from what is found in the consecutive layers in both phases. The orientational preferences of the water molecules also vanish beyond the first molecular layer. Further, water molecules form a strongly percolating two-dimensional, lateral hydrogen-bonding network in the first layer, but this lateral, intralayer percolation network does not exist in the subsequent molecular layers. The two surfaces covering the two liquid phases are found to behave largely independently from each other. Thus, at some parts of the interface, typically at positions where the water surface is locally convex and the DCM surface is locally concave, i.e., where the water phase forms tips penetrating somewhat into the DCM phase, the two surface layers can be in close contact with each other. On the other hand, at some other points of the interface, typically where the water surface is locally concave or the DCM phase is locally convex, relatively large voids can be located between the two phases.