Aggregation phenomena in a lecithin-based gel: Transient networks and diffusional dynamics

The diffusional properties in the cyclohexane/lecithin/water gel are invest igated by means of quasielastic neutron scattering and depolarized light sc attering. Also the pure organic solvent and sol phases of different composi tions are investigated for a comparison. It is found that both translationa l and rotational diffusion of water and lecithin are strongly correlated, a nd become faster in the gel phase. This does not fit the current point of v iew, where the rheological properties of the system are supposed to result from the entanglement of giant linear micelles which grow up under addition of water. As a further investigation, the aggregative phenomena occurring in the system at the sol-gel transition are observed by means of a calorime ter tao. Also in this case, the interpretation of the experimental data in terms of the growth of linear giant aggregates leads to some inconsistencie s. It is suggested that the macroscopic shear viscosity behavior can be tho ught of as originated by a transient network determined by cooperative inte rmicellar interactions, where the role played by water is not as simple as assumed up to now. [S1063-651X(99)03401-7].