Abstract

Knowledge of structure and properties of water molecules near hydrophobic interfaces is crucial for understanding many important fundamental and applied surface problems involving water. For instance, microscopic understanding of wetting or non-wetting of an interface by water molecules is one of those important but still open problems. The subject has motivated and stimulated a number of theoretical studies with numerical calculations in the past.¹ However, because of the lack of suitable techniques, experimental studies on the subject have been rare or nonexistent. We show in this paper that it is possible to use sum-frequency generation (SFG) to obtain vibrational spectra of water at hydrophobic interfaces, and the results show that hydrophobicity is characterized by the appearance of dangling OH bonds on 25% of the surface water molecules. Moreover, our results show that the structure of water molecules depends on interface rigidity.

© 1994 IEEE