In one, by Mo Β¨hwald (13), the emphasis is on the During the liquid expanded/ liquid condensed (LE /LC) phase experimental observations; and in the other, by McConnell transition, the long range repulsive interactions among fatty acid (14), the emphasis is on the quantitative understanding of or phospholipid molecules induce the formation of a dispersion the intriguing structures developed during the LE/LC transiof LC islands (of almost the same size ) as a superlattice in a tion. The experimental observations clearly indicate that the continuous phase of LE molecules. Assuming that the transformatransition does not occur via the formation of a new bulk tion occurs at thermodynamic equilibrium, one demonstrates that, phase; it takes place through the formation of a two-dimenas the surface fraction of LC phase increases, the surface pressure sional microemulsion of the new phase in the old one, with p increases. Consequently, the LE/ LC transition can have characthe islands of the microemulsion organized as a superlattice. teristics different from those of the conventional first order transitions. α§ 1997 Academic Press As noted by McConnell, the long range dipole-dipole inter-Key Words: monolayer; polar molecules; liquid expanded/liquid actions are mainly responsible for the formation of the iscondensed transition.
lands. Indeed, the repulsive free energy can be minimized by splitting the hypothetical bulk phase in a number of islands; the splitting is, however, limited by the increase in