Retardation of Water Reorientation at the Oil/Water Interface

Molecular dynamics simulations reveal the retardation of water reorientation at the oil/water interface, which is mainly contributed by the slow reorienting interfacial water molecules with hydrogen bonds donated to other interfacial water. On the basis of the extended jump model, the retardation of water reorientation is explained to be mainly caused by the slowed hydrogen bond exchange, with a minor contribution of the slowed frame reorientation. The excluded volume effect due to the space occupied by the hydrophobic phase predicts a retardation factor higher than that observed. It is deduced that the increased transition state density for hydrogen bond exchanges at the interface compensates this effect to some extent. Water reorientation dynamics at the oil/water interface exhibits differences as compared to those reported around hydrophobic groups, next to a hydrophobic solid surface and at the air/water interface. Free dangling OH bonds at the interface have little influence on overall water reorientation. The transitions between free and hydrogen-bonded OH bonds are active at the interface.