Single-particle dynamics of water molecules confined in a lecithin-based gel

We present experimental measurements, obtained by a quasielastic neutron scattering experiment, of the self-diffusion coefficient of water confined in the dense structure of lecithin-based gels. The inelastic neutron scattering (INS) technique was also used to monitor the dynamic state of water molecules involved in the gel structure. It is shown that, at least in highly concentrated systems, the diffusional properties of water can be related with the growth process of wormlike aggregates. However, an interpretation of our data consistent with a number of experimental results in the literature and with INS indications requires the adoption of a model in which the gel structure is better described in terms of percolating aggregates rather than the usually described polymerlike entangled (not interconnected) network. In such a way, we are pointing out the existence of an interpretative controversy calling for further investigation to be disentangled. The source of the inconsistencies is found in the commonly accepted basic assumption of the existence of a simple scaling law, relating the average micellar length to the concentration. [S1063-651X(99)04312-3].