Potential Dependent Alignment and Hydrogen Bonding of Water Molecules at Charged Air/Water and CCl4/Water Interfaces

We observe potential dependent alignment and hydrogen bonding of interfacial water molecules at a charged air/water and CCl4/water interface. The interfacial potential is a result of the presence of charged soluble surfactant adsorbed to the interface. We vary the interface potential by changing the surface charge density, the ionic strength, and the temperature while monitoring OH stretching modes sensitive to the structure and hydrogen bonding of interfacial water molecules. As the potential is increased at the air/water interface we observe a progression from a waterlike and less hydrogen bond ordered structure to an icelike and more hydrogen bond ordered structure. This progression is a direct consequence of the induced alignment of the interfacial water molecules resulting from the large electrostatic field produced in the interfacial region by the charged surfactant. Temperature dependence measurements confirm the conclusion that there is a potential dependent alignment of the interfacial water molecules. In comparison, at the CCl4/water interface we observe only the icelike structure both in the presence and absence of a charged surfactant. The structural difference observed at the air/water and CCl4/water interfaces is discussed within the context of the structure imposing effect the nonpolar CCl4 molecules have on the interfacial water molecules.