Lecithin Microemulsion Gels: A NMR Study

Lecithin gels in cyclohexane have been studied by NMR spectroscopy with a multinuclear approach. A precise correlation exists between previously published1-4 shear viscosity, a macroscopic property, and the line width of the P-31 NMR resonance. At constant water/lecithin ratio (W0 = 8) near the condition of maximal shear viscosity, the P-31 spin-spin relaxation time as a function of lecithin concentration defines the range in which a gel-forming condition is present. Light scattering data i.e. hydrodynamic and gyration radii5 at low lecithin concentration as a function of W0 match extremely well the corresponding P-31 line width curve. During the gel formation process water mobility increases and, contrary to the expectation based on the established model, no evidence of fatty chains entanglement is found. Instead a marked stiffening of the trigliceride moiety and the phosphate is found, while the polar head and the fatty chains do not show loss in mobility.