For the case of single-chain fatty acids, it was later shown that the isotherms approach zero slope as the material used is progressively purified[@Pallas].

On the theoretical side, the LE/LC transition has been modeled based on various microscopic pictures of the interaction between surfactant (or lipid) molecules including translational as well as internal degrees of freedom[@Marcelja; @Bell; @Georgallas; @Chen; @Kramer].

The biological function of membranes depends mostly on the incorporation of proteins and other macromolecules into the lipid layers. Functionality and efficiency of these inclusions depend crucially on microscopic details of the embedding in the lipid matrix, which can occur in different ways. Monolayers at the air-water interface are suitable for the study of the interaction between lipids and proteins, since they are rather well-defined and allow the control of independent thermodynamic parameters which are otherwise fixed in a bilayer membrane, like the area per molecule. Also, the observational techniques are well developed. Direct visualization of the phase behavior of monolayers can be obtained using fluorescence microscopy techniques. Here, a fluorescent dye probe is incorporated into the monolayer the lateral distribution of which can be obtained from the analysis of fluorescence micrographs. Contrast in the images is obtained as a 