Formation of Unique Unilamellar Vesicles from Multilamellar Vesicles under High-Pressure Shear Flow.

Vesicles in surfactant systems are influenced by a shear field. The high shear flow generated by a homogenizer is expected to affect the size of vesicles. Hence, it should be possible to control the size and dispersion of vesicles by tuning the shear. In this study, the influence of shear on the vesicle phase was studied by measuring the rheology and conductivity of a solution made of the nonionic surfactant trideceth-5, a polyethylene glycol ether of tridecyl alcohol with an average number of ethylene oxide of 5, and the anionic surfactant sodium dodecylsulfate. It was found that when shear was applied by a homogenizer, the bilayers of the multilamellar vesicles were stripped off and became unilamellar vesicles, which decreased the viscoelasticity of the system. However, because of the pressure provided by the homogenizer, the newly formed unilamellar vesicles were small and the relative distance between them was large. As a result, the vesicles were no longer crowded and could easily pass each other under shear. This is why the unilamellar vesicles generated by the homogenizer had low viscoelasticity and flow birefringence. Additionally, it took a long time for the unilamellar vesicles to relax back to the original state.