Properties of the Liquid–Vapor Interface of Acetone–Water Mixtures. A Computer Simulation and ITIM Analysis Study

Abstract

Molecular dynamics simulations of the liquid–vapor interface of acetone–water mixtures of different compositions, covering the entire composition range have been performed on the canonical (N, V, T) ensemble at 298 K, using a model combination that excellently describes the mixing properties of these compounds. The properties of the intrinsic liquid surfaces have been analyzed in terms of the Identification of the Truly Interfacial Molecules (ITIM) method. Thus, the composition, width, roughness, and separation of the subsurface molecular layers, as well as self-association, orientation, and dynamics of exchange with the bulk phase of the surface molecules have been analyzed in detail. Our results show that acetone molecules are strongly adsorbed at the liquid surface, and this adsorption extends to several molecular layers. Like molecules in the surface layer are found to form relatively large lateral self-associates. The effect of the vicinity of the vapor phase on a number of properties of the liquid phase vanishes beyond the first molecular layer, with the second subsurface layer already part of the bulk liquid phase in these respects. The orientational preferences of the surface molecules are governed primarily by the dipole–dipole interaction of the neighboring acetone molecules, and hydrogen bonding interaction of the neighboring acetone–water pairs.