Implications for the Phase Behavior

In the Winsor III state, the oil and water phases represent weak molecular solutions of the surfactant in the solvents. On the other hand, the structure of the surfactant phase is quite intriguing. Because the spontaneous curvature is small, the siufactants associate into structures of zero, or low, curvature, which are either lamellar liquid crystals with = H2 — 0, or a sponge-like bicontinuous microemulsion phase, where the surface has a locally saddle shape Hi —H2. It is believed that lamellar phases are favored for rigid surfactant monolayers, with K 10 keT, while bicontinuous microemulsion phases are favored for flexible monolayers, with k 1 AbT.  

So far, we have been concerned with the interfacial tension (a = aof a planar emulsion film in equilibrium with a micellar solution. If the emulsion film is curved to the mean curvature H, the interfacial tension is expected to 

The interfacial tension of a curved film has a minimum at H = Ho, where the spontaneous curvature is equal to the curvature of the film. Note that this monolayer Ihistration correction applies only to the saturated surfactant mono-layers and is different from the well-known Tolman curvature correction to the surface tension, which applies to much higher curvatures. 

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Borick S., Debenedetti P., Sastry S. (1995) A Lattice Model of Network-Forming Fluids with Orientation-Dependent Bonding Equilibrium, Stability, and Implications for the Phase Behavior of Supercooled Water, JChem. 99(11), 3781-3792. 

S. S. Borick, P. G. Debenedetti, S. Sastry, A lattice model of network-forming fluids with orientation-dependent bonding— equilibrium, stability, and implications for the phase-behavior of supercooled water, J. Phys. Chem. 99 (1995) 3781-3792. 

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