PHOSPHOLIPIDS AS EMULSION STABILIZERS .2. PHASE-BEHAVIOR VERSUS EMULSION STABILITY

The equilibrium phase behavior and the macroemulsion type and stabilit y of oil-water-lecithin mixtures was studied, For dioleyl phosphatidyl choline (DOPC) and n-alkanes as the oil component, the phase equilibri um is characterized by an extended inverse micellar region in equilibr ium with water (Winsor II), On the other hand, n-C8F18-DOPC-water and soybean oil-DOPC-water mixtures show a three phase equilibrium of almo st pure water, almost pure oil, and lamellar phase L(alpha) (Winsor II I), Equilibrium phases of DOPC systems can be emulsified in each other , Inverse W/O macroemulsions are favored for all the n-alkanes (C-6-C- 14) studied; O/W emulsions are rather unstable. On the other hand, n-p erfluorooctane and soybean oil produced very stable O/W emulsions, The phase behavior and emulsion stabilizing properties of an egg yolk pho spholipid mixture is similar to those of DOPC. The phase equilibrium o f the saturated analogue of DOPC: distearoyl phosphatidylcholine (DSPC ) in mixtures with alkanes and water at room temperature is different and characterized by a Winsor III equilibrium of a L(beta) lamellar ph ase in a gel state, oil and water, Accordingly, the O/W emulsions are strongly favored to inverse systems. The pattern of the phase equilibr ium and macroemulsion stability becomes similar to that of DOPC at ele vated temperatures, The macroemulsion stability pattern versus the pho spholipid packing type is discussed in relation to the recently propos ed theory of emulsion stability to coalescence (Kabalnov, A. and Wenne rstrom, H., Langmuir 12, 276 (1996)). (C) 1996 Academic Press, Inc.