Lipid and Polyampholyte Monolayers to Study Polyelectrolyte Interactions and Structure at Interfaces

Lipid and polyampholyte monolayers are shown to constitute interesting models for study of electrostatic and steric interactions of polyelectrolytes at interfaces. Measurements with Langmuir monolayers at the air/water interface yield access to the energetics and kinetics of adsorption processes. Newly developed types of optical microscopy, X-ray diffraction, and reflection techniques yield fine structural details, for example lipid structure, segment density profiles, and domain structure. Scanning probe microscopy enables resolution of adsorbate structure on solid surfaces which proves to be most interesting for polyampholytes, for which the charge density can be varied via pH. The results can only partly be explained by theory. Unexpected and not yet explained findings are attractive interactions of polyelectrolytes and interfaces and long-range interactions affecting kinetics and micro phase separations. They can, however, be used as a primary means of controlling interface properties and structure.