Lecithin microemulsion gels: an 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 31P NMR resonance. At constant waterllecithin ratio ( WO = 8) near the condition of maximal shear viscosity, the 3lP 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 radii6 at low lecithin concentration as a function of WO match extremely well the corresponding 3lP 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.