RAMAN-SPECTROSCOPY OF LANGMUIR MONOLAYERS AT THE AIR-WATER-INTERFACE

A new approach for the acquisition of Raman spectra of Langmuir layers at the air-water interface is presented. Colloidal Ag is grown electr ochemically under layers of the anionic surfactants stearic acid and d ipalmitoylphosphatidic acid sodium salt (DPPA) on an aqueous AgNO3 sub phase. The Ag colloid layer supports surface-enhanced Raman scattering (SERS) of the Langmuir layers with minimal interference from the subp hase. Spectra of good signal-to-noise ratio have been acquired. These spectra are interpreted in terms of the headgroup chemistry and the de gree of alkane chain order as a function of surface pressure.