Viscoelastic properties of concentrated dispersions in water of soy lecithin

Viscoelastic properties of soy lecithin dispersions at 60, 120, 180 and 240 g l-1 in water have been studied as a function of ionic strength (NaCl concentrations in the range 10-5-10-2 mol l-1) and of preparation method (sonication, freezing-unfreezing). Viscosity measurements of sonicated dispersions in a rotatory viscometer show Newtonian and plastic (Bingham) behavior, whereas the frozen-unfrozen dispersions show a spectacular change in their viscoelastic properties, that is, a non-Newtonian behavior with pseudoplastic characteristics and rheopexy. These properties have been related to electrokinetic characteristics of the segregated vesicles in each case. A decrease in ζ-potential (in absolute value) of vesicles results on an increase in the hysteresis loop area of the parents dispersions.