Thinning and thickening effects induced by shearing in lecithin solutions of polymer-like micelles

The effects of shear flow on the lecithin organogels consisting of reverse polymer-like micelles have been investigated by dynamic rheology. It was es tablished that the shear effects depended on the molar ratio of water to le cithin that determined the micellar type in the system. For an organogel wi th linear flexible polymer-like micelles, thinning was observed. The main f eatures of the rheological behavior bore a resemblance to previously invest igated aqueous systems made up of similar but direct polymer-like surfactan t micelles. The thinning effects are explicable on the basis of alignment o f micellar aggregates along the flow direction and their disentanglement. A n organogel with branched micelles did not demonstrate any notable response to the shearing. Unusual behavior was noticed in the case of a jelly-like phase that included the highest amounts of water. The applied steady shear flow induced a thickening effect. This was followed by restructuring of the micellar system at the level of polymer-like micelles and their network. T he shearing effects were characterized by slow kinetics, in addition, the s ystem did not revert to the original state after the cessation of steady sh ear flow even within 8 h. Measurements performed in an oscillation regime o n this system showed that shearing should promote a substantial growth of t he polymer-like micelles and affect their alignment.