Dynamical properties of lecithin-based microemulsions

Lecithin/isooctane/water gel is investigated by means of different experimental techniques, namely, depolarized light scattering, ultrasonic and dielectric measurements. Pure isooctane and lecithin/isooctane solution are also tested for comparison. A relaxation process, taking place in the 10−13 s time scale was revealed from the light-scattering experiment, both in the gel and in the solution. This is attributed to the reorientational relaxation of the solvent that keeps its bulk properties. The comparison between the activation enthalpies for the detected process in the gel and in the solution, together with the behavior of the relaxation times vs frequency showed the existence of some influence of the entangled network on the isooctane dynamics. Data from ultrasonic measurements show the existence of the same relaxation process, both in the gel and in the solution, with a relaxed value very near to the one obtained for pure isooctane. The observed dynamics were interpreted as due to the existence of the same elementary microspheres of lecithin in the bulk of the solvent in both systems. The relaxation phenomenon revealed by the dielectric data was analyzed in the frame of a Cole-Cole phenomenological law and associated to the role played by water molecules on lecithin reorientation. The temperature dependence of the observed phenomenon is in agreement with the existence of an entangled polymeric-network.