Vibrational Spectroscopy of Molecules at Liquid/Liquid Interfaces.

Measurement of the nonlinear vibrational spectrum of molecules at a liquid/liquid interface has recently been achieved by the use of total internal reflection sum frequency vibrational spectroscopy (TIR SFVS). This report describes this nonlinear optical technique and gives examples of the type of information which has been obtained about interfacial water and surfactants adsorbed at this interface. The surfactants examined include simple alkyl cationic and anionic surfactants commonly used in cleaning products, and phosphatidylcholines which comprise the major component of cell membranes. Studies of interfacial water involve comparative studies at air/water and oil/water interfaces, and the effect of adsorbed surfactant on the water structure and orientation at these two interfaces.