Phase behavior of reverse microemulsions based on Peceol(®)

Abstract

The phase diagram of the four component system Peceol®/lecithin/ethanol/water was studied at 25°C and at a fixed fraction of ethanol. It shows an isotropic W/O microemulsion phase, biphasic liquid system and Liquid crystalline phases. The stabilizing effect of lecithin with the fluidifying effect of ethanol on the microemulsion based on long chain glycerides provides an effective combination to solubilize a large amount of water. Some structural transitions in the phase diagram were investigated as a function of water content using conductivity, rheology, Karl Fisher titration, optical microscopy and SAXS measurements. The results show no change in the microstructure of the isotropic liquid upon phase separation in the liquid biphasic area. However, in the water rich region, migration of ethanol to the external aqueous phase at the expense of the saturated microemulsion promotes the formation of liquid crystalline phases. As a function of water content, the structural change to the liquid crystalline phases follows: isotropic phase L2 → Inverted hexagonal phase H2 → Inverted hexagonal H2/lamellar Lα phases.

Keywords: Microemulsion; Phase diagram; Phase transitions; Polar lipids; Rheology; SAXS.