Comparisons Of The Structure Of Water At Neat Oil Water And Air Water Interfaces As Determined By Vibrational Sum Frequency Generation

We have employed vibrational sum frequency generation (VSFG) to investigate the structure of water at neat oil/water and air/water interfaces through the OH stretching modes of the interfacial water molecules. We find that at the oil/water interface the prevailing structure of the water molecules is a tetrahedral arrangement much like the structure of ice while at the air/water interface we observe an equal distribution between an ice-like and a less ordered water like arrangement. The relationship between the structure of the interfacial water molecules and the properties of the other fluid (air or oil) is discussed in terms of hydrogen bonding at the interface. We also compare our results to previous VSFG studies at similar interfaces and find a difference in the spectra obtained from the oil/water interface.