New lecithin organogels from lecithin/polyglycerol/oil systems

New liquid substances that induce the formation of lecithin organogels composed of reverse worm-like micelles were studied. The phase behavior and rheological properties of lecithin/polyglycerol (PGL)/oil systems were investigated in detail; the polymerization degrees of the glycerol residues were 3, 4, 6, 10, 20, and 40. From the partial phase diagrams of the lecithin/PGL/n-decane systems, it was apparent that highly viscoelastic reverse worm-like micelles formed upon the addition of small amounts of the PGL, except in the case of the PGL with a polymerization degree of 40. Steady-flow viscosity measurements showed that the zero-shear viscosity (η₀) of the reverse worm-like micelles rapidly increased with the concentration and polymerization degree of the PGLs, reaching a maximum value that was 750,000 times the viscosity of n-decane and thus resulting in the growth of these micelles. It is noteworthy that the η₀ values of lecithin organogels formed using PGLs were higher than the η₀ value of the lecithin organogel formed using glycerol (GL). From dynamic viscoelasticity measurements, it was shown that the viscoelastic behavior of the reverse worm-like micelles was consistent with the single Maxwell model, which is the basic model of a viscoelastic body. It follows from this study that PGLs are useful liquids because they can induce the formation of lecithin organogels with high viscoelasticity, as do other liquids such as water, glycerol, ethylene glycol, and formamide.