Sum-frequency spectroscopic study of Langmuir monolayers of lipids having oppositely charged headgroups.

Sum-frequency vibrational spectroscopy, with the help of surface pressure-area (π-A) isotherm, was used to study lipid Langmuir monolayers composed of molecules with positively and negatively charged headgroups as well as a 1:1 neutral mixture of the two. The spectral profiles of the CH(x) stretch vibrations are similar for all monolayers in the liquid-condensed (LC) phase. They suggest a monolayer structure of closely packed alkyl chains that are nearly all-trans and well oriented along the surface normal.

Imaging of collapsed fatty acid films at air-water interfaces.

In situ imaging ellipsometry is employed to monitor the morphology of collapsed films of fatty acid Langmuir monolayers on pure water and on CaCl2 solution. The ellipsometry images reveal the existence of multilayer domains in the collapsed region, and analysis of the images yields the thicknesses of these domains. The multilayer films formed on water are mainly trilayers, while those on CaCl2 solution are mainly bilayers.