Molecular dynamics simulation of the water/2-heptanone liquid-liquid interface

Molecular dynamics simulations were performed to study the structural and d ynamic properties of the water/2-heptanone (HPT2) liquid/liquid interface. It was found that HPT? forms a bilayer structure at the interface, pointing its polar heads into the aqueous phase. Water molecules penetrate the hydr ophilic headgroup region but not the hydrophobic core. At the hydrophilic r egion water molecules establish hydrogen bonds with the ketone oxygen of th e HPT2 molecule. Behind that zone, the water molecules show a preference in keeping their dipoles in the interfacial plane and these orientations rema in in two or three molecular layers. The water dipole distribution is sligh tly asymmetric, having an average excess in the resulting component normal to the interfacial plane. The water dipoles point toward the aqueous phase for waters in the aqueous side of the interface and into the organic phase for water molecules in the organic side of the interface. The water structu re remains almost unchanged at the Gibbs dividing surface. The HPT2, struct ure is not so robust, and near the interface it is distorted by the presenc e of the aqueous phase. Self diffusion exhibits long range anisotropy, diff usion toward the interface being slower than diffusion in the interfacial p lane. The water orientational dynamics is slowed down near the interface. T he HPT2 reorientation becomes anisotropic at the interface as reorientation s perpendicular to the interface an slower than those in the interfacial pl ane. The interface was found to be sharp, highly corrugated, and broadened by capillary waves.