States of Lipid Monolayers Spread on Water Surface

4 States of Lipid Monolayers Spread on Water Surface 

One is quite familiar with the changes one observes in matter going from solid to liquid or vice versa with temperature or pressure. It is found that even a monolayer of lipid (on water) when compressed can undergo various degrees of packing states. This is somewhat similar to three-dimensional structures (gas-liquid-solid). In the following, the various states of monomolecular film will be described as measured from the surface pressure, n, versus area, A, isotherms, in the case of simple amphiphile molecules. On the other hand, the O-A isotherms of biopolymers will be described separately, since these are found to be of different nature. 

This change in packing thus is analogous conceptually to the three-dimensional P-V isotherms, as are well known from the classical physical chemistry (Adamson and Gast, 1997 Birdi, 1989 Bouvrais et al 2014 Gaines, 1966). We know that as pressure, P, is increased on a gas in a container, when T T , the molecules approach each other closer and transition to a liquid phase takes place. Further compression of the liquid state results in the formation of a solid phase. 

The alkyl-alkyl groups attraction arises from the van der Waals forces. The magnitude of van der Waals forces increases with 

Decrease in distance between molecules (or when area/molecule [A] decreases) 

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