MONOLAYER STRUCTURE AT GAS-LIQUID AND GAS SOLID INTERFACES - INFRARED REFLECTANCE SPECTROSCOPY AS A PROBE

Within recent years, external reflection-absorbance infrared spectroscopy has been adapted to the study of conformation-sensitive vibrational modes in amphiphilic monolayers at nonmetallic surfaces. Included in this group is the class of monomolecular films that form ordered two-dimensional arrays at the air-water (A/W) interface. It has proven possible to investigate the surface-induced first order thermodynamic phase transition of phospholipid monolayer films at the A/W interface using this technique. Results of this work have focused on describing the nature of the phase transition, the design of an automated Langmuir-type film balance and its interfacing to the spectrometer, and the construction of a model to describe the orientation of the vibrational dipole moments based on the polarized reflectance spectra. In addition, the ability to probe the A/W interface allows us to directly compare the IR spectra of in-situ monolayers with the spectra of monolayer films transferred to attenuated total reflectance (ATR) crystals using classical Langmuir-Blodgett technique, in order to determine whether the physical process of transfer disrupts the structure of the monolayer film.