Phase behavior of sodium naphthenates, toluene, and water

In a ternary phase diagram of sodium naphthenates (SN), toluene, and water the following phases can be formed at 25 degreesC: normal micellar solution; inverse micellar solution; lamellar liquid crystal; microemulsion; and turbid birefringent gel phase. The turbid gel phase contains lamellar liquid crystal structures. The SN is a mixture of many individual components. This is the reason that no saturation concentration was found for SN in toluene and that there is only one single-phase range in the entire phase diagram. Large differences in W/O emulsion stability were observed within very small composition ranges. The emulsion had low stability within the L1 and L2 two-phase and in the vicinity of the microemulsion phase range. In the presence of a liquid crystal phase, the emulsion was very stable even within the multiphase range containing the microemulsion phase. The increased interface rigidity caused by the presence of the liquid crystal layer on the O/W interface is suggested as an interpretation of the observed increase in the emulsion stability. (C) 2001 Academic Press.