FORMATION OF AOT BRINE MULTILAMELLAR VESICLES

A rheo-optic study of the formation kinetics of the multilamellar vesi cle (MLV) structure in the AOT/brine system is reported. Controlled sh ear rate rheology and flow dichroism are used to identify a critical s hear stress below which MLVs are formed and above which a transition t o a biphasic state occurs. Controlled stress rheology with in situ flo w small-angle light scattering shows that MLV formation occurs at a cr itical strain that is signaled by shear-thickening behavior and small- angle scattering typical of spherulites. Further, the applied shear st ress controls both the MLV formation rate and the final MLV size. At h igh stresses shear-induced ordering of the MLVs is observed, similar t o that seen in colloidal suspensions, as well as a transition to a bip hasic state. The results are used to reinterpret previously published' ' nonequilibrium phase diagrams'' and to test scaling models for the M LV size in the pure MLV phase.