Estimation from structural group contributions systems

By the hydrophilic-lipophilic balance (HLB) system, according to Griffin (15). The HLB ratio is expressed as a number based on the emulsifying properties of the emulsifier. The HLB can also be estimated from the chemical structure according to the molecular group contributions, as repeated by Davies (16). HLB numbers are closely related to the functional properties of the emulsifiers. 

Phase Transitions in Lipid Assemblies. The rich polymorphism of amphiphilic systems, of which the multilamellar and the Hn phases are only two structures, was made evident from the seminal work of Luzzati and co-workers. Since that early work, an immense variety of water-induced phase transitions have been observed and rationalized in terms of an apparently systematic connection between water content and polar group molecular area. Therefore, the recent observation of a double transition—Hn to lamellar back to Hn—from continual hydration of dioleoylphosphatidyl-ethanolamine (40) was a surprise. Furthermore, an estimate of the cost of uncurling the monolayer in the formation of bilayers based on the previously described bending modulus far exceeds the osmotic work that actually produced the transition. Although this transition sequence can successfully be accounted for by simple thermodynamical principles, it, in fact, contains many geometry-dependent free energy contributions that we simply do not yet understand (41). 

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