Liquid crystallinity of lecithin systems. Ternary phase diagrams of lecithin—water with triton X-100 and decanol

Abstract

The isothermal phase diagrams for two ternary systems of soybean lecithin—water with Triton X-100 and decanol have been determined by water deuteron NMR and polarizing microscopy methods. The lamellar phase formed in the binary lecithin systems is found to swell and take up more water by the addition of both Triton X-100 and decanol, but the swelling is more pronounced in the presence of Triton X-100. Two isotropic solution phases, one water-rich (L 1) and the other rich in Triton X-100 (L 2), separated by a hexagonal liquid crystalline phase, form in the aqueous Triton X-100 system. The hexagonal, L 1, and L 2 phases can solubilize 5, 10, and 5 wt% lecithin, respectively, and they form mixed aggregates. The solubility of lecithin in pure Triton X-100 is limited. On the other hand, lecithin is highly soluble (62%) in decanol in which about 18% water can also be dissolved. The decanol system also yields a cubic liquid crystalline phase with both high lecithin and water contents and this phase occupies a very narrow region in the triangle. The swelling of the lamellar liquid crystalline phase can be understood with the hydration force based on the electrostatic continuum theory. The calculated phase diagram is found to agree fairly well with that constructed from the experimental data.