Phase Behavior of the Lecithin/Water/Isooctane and Lecithin/Water/Decane Systems

Abstract

The isothermal pseudo-ternary-phase diagram was determined at 25 degrees C for systems composed oflecithin, water, and, as oil, either isooctane or decane. This was accomplished by a combination of polarizing microscopy, small-angle X-ray scattering, and NMR techniques. The lecithin-rich region of the phase diagram is dominated by a lamellar liquid-crystalline phase (Lalpha). For lecithin contents less than 60% and low hydration (mole ratio water/lecithin = W0 < 5.5), the system forms a viscous gel of branched cylindrical reverse micelles. With increase in the water content, the system phase separates into two phases, which is either gel in equilibrium with essentially pure isooctane (for lecithin < 25%) or a gel in equilibrium with Lalpha (for lecithin > 25%). These two-phase regions are very thin with respect to water dilution. For 8 < W0 < 54 very stable water-in-oil emulsions form. It is only after ripening for more than 1 year that the large region occupied by the emulsion reveals a complex pattern of stable phases. Moving along water dilution lines, one finds (i) the coexistence of gel, isooctane and Lalpha, (ii) equilibrium between reverse micelles and spherulites, and, finally, (iii) disconnected reverse micelles that fail to solubilize water for W0 > 54. This results in a Winsor II phase equilibrium at low lecithin content, while for lecithin > 20% the neat water is in equilibrium with a reverse hexagonal phase and an isotropic liquid-crystalline phase. The use of the decane as oil does not change the main features of the phase behavior.

Structure and dynamics of a sponge phase in the methyl δ-aminolevulinate/monoolein/water/propylene glycol system

“…3a in Ref. [28]). In the polarizing microscope the texture of the phase with 16% m-ALA was almost identical to the one in Fig.…”

Development of pharmaceutical clear gel based on Peceol®, lecithin, ethanol and water: Physicochemical characterization and stability study

“…As demonstrated by several studies, lecithin microemulsion was formed without alcohol by substituting triglyceride by mineral oil (e.g. alkane and cycloalkane) [17][18][19][20]. A transition from spherical to flexible cylindrical reverse micelles was observed upon addition of small amount of water to the lecithin microemulsion [21][22][23][24][25].…”

Phase equilibria of mixtures of surfactants and viscoelastic properties of the liquid crystal phases

“…Up to now, the phase behavior of ternary systems composed by ionic surfactant/alcohol/ water [7e10] and by surfactant/oil/water [3,7,11] has been extensively studied. Much lesser studies of ternary mixtures of two surfactants and water in the whole range of concentrations have been reported [12].…”