SUPERIMPOSED ORDERING TRANSITIONS IN PHOSPHOLIPID MONOLAYERS

ordered states and phase transitions in phospholipid monolayers have been investigated by a combination of fluorescence microscopy and spectroscopic techniques, thermodynamic measurements and fusion experiments with domains applying defined electrostatic fields. The results are also discussed and interpreted molecularly using the available data from X-ray diffraction and reflectivity as well as from electron optical experiments and surface potential measurements. A phase diagram is suggested where first order transitions "fluid" - "liquid crystalline" are super-imposed on various higher order transitions. In gel phase domains the lipid chains from a two-dimensional lattice rich in dislocations which can be excited thermally. Furthermore, their order is disturbed by the lipid head group probably not forming an autonomous lattice within the plateau region of the isotherms but showing a secondary structure.