Effect of Hydrogen Bonding between Water Molecules on Their Density Distribution near a Hydrophobic Surface

The number and energy of hydrogen bonds that a water molecule forms in the vicinity of a hydrophobic surface differ from their bulk values. Such an alteration gives rise to a hydrogen bond contribution to the external potential field whereto a water molecule is subjected in the vicinity of a hydrophobic surface. This contribution is repulsive and can be determined by using a recently developed probabilistic approach to water–water hydrogen bonding. Combining the probabilistic approach with the density functional theory, we have found that the hydrogen bond contribution to the external potential plays a crucial role in the formation of a thin depletion layer (of thickness of a molecular diameter and of very low density) between liquid water and hydrophobic surface.