Shear-induced transition of originally undisturbed lamellar phase to vesicle phase

We have studied the transformation of an L-alpha phase composed of stacked bilayers to a vesicle phase under the influence of shear. The ionically charged stacked bilayer phase was prepared by protonation of an L-3 phase from tetradecyldimethylamine oxide hexanol, and water. The protonation was accomplished by a hydrolysis reaction; of an ester solubilized in this phase. By the protonation of the bilayers the L-3 phase becomes unstable and, in the absence of shear, is transformed into a classical lamellar phase. This low viscosity phase was then transformed into an onion phase by shear. The structural changes during this transformation process were monitored by means of scattering experiments and by rheological and conductivity measurements under shear. The following results were obtained when the shear rate was varied: (a) the transition from stacked lamellae to vesicles is irreversible and does not go back; (b) the formation of multilamellar vesicles requires a total strain of about 2000 (for a given surfactant concentration of 100 mM). In addition the influence of various parameters on the transformations of the L-alpha phase was studied, such as chain length of the surfactant, chain length of the alcohol, and the total concentration of amphiphile.