Molecular Dynamics Simulation of the Liquid–liquid Interface for Immiscible and Partially Miscible Mixtures

Abstract

Molecular dynamics (MD) simulations were performed on model interfaces between n-hexane and water and between water and 1-hexanol. The SPC/E model was used for water. Organic molecules were modeled with united atom potentials located at heavy nuclei, but included explicit modeling of the alcohol H. The structure of the interface was examined in terms of its position, thickness, roughness, and molecular orientations. Additionally, self diffusion coefficients in each phase and the interfacial tension were determined. Significant differences in the interfacial structure were found between the immiscible and partially miscible systems. The interface for the immiscible system is molecularly sharp with only small dynamic waves or corrugation. On the other hand, the interface in the partially miscible system consists of a molecularly sharp region and a bilayer of hexanol oriented with the OH heads out. Relatively static waves corrugate the inner part of the interface considerably more than that for the immiscible system. Water solubility in the hexanol phase occurs in hydrogen bonded cages formed by the OH groups of the alcohol.