Structure and Dynamics of the Liquid–Liquid Interface of an Aqueous NaCl Solution with Liquid Carbon Tetrachloride from First-Principles Simulations

Abstract

The present work deals with a first-principles theoretical study of the liquid–liquid interfacial system of an aqueous NaCl solution with the hydrophobic liquid of carbon tetrachloride (CCl4). Various structural and electronic properties of the system such as the inhomogeneous density profiles of ions and water molecules, hydrogen bond distributions, orientational profiles, vibrational frequency distributions, and also dipole moments of water at the bulk and interface are investigated. It is found that the chloride ions have a higher propensity for the interface and the sodium ions have a tendency to reside in the inner side of the aqueous medium. The dynamical aspects of the interfaces are analyzed in terms of the diffusion, orientational relaxation, hydrogen bond dynamics, and vibrational spectral diffusion and are compared with those of the bulk regions. It is found that the interfacial molecules have a faster diffusion and orientation relaxation with respect to the bulk molecules. The interfacial water molecules are also found to have a shorter hydrogen bond lifetime than those of bulk water molecules. We have also investigated the dynamics of vibrational frequency fluctuations of water molecules in the bulk and interfacial regions.