Destruction of the Water Layer on a Hydrophobic Surface Induced by the Forced Approach of Hydrophilic and Hydrophobic Cations

Structural change of the water layers is the primary step for the direct interactions among the hydrated substances in aqueous solutions. We have studied how the water layers on a solid surface is destroyed by the approach of several hydrophilic and hydrophobic cations, which are used as model substances. The combined use of electrochemical system and IR spectroscopy enables the study of the destruction process of water layers during the close contact among them. We have observed for the first time that hydrophilic cations cause greater destruction of the interfacial water structure than hydrophobic cations. This result is ascribed to the different orientations of water molecules around the cations; H-bonds around hydrophilic cations expand toward the outer hydration shells, while they are closed inside the primary shell in the case of hydrophobic cations. These different orientations of water molecules cause different effects on the interfacial water structures.