Flow induced deformation of multilamellar surfactant vesicles

The morphology of surfactant systems is a topic of high scientific and industrial interest. However, while many studies have been addressed to the phase behaviour of surfactants in water, only limited information is available in literature on flow-induced morphology of such systems. Depending on concentration, different static morphologies have been observed, such as lamellae and vesicles. In this work, we present the first quantitative investigation of the flow behavior of single surfactant multilamellar vesicles using a video-microscopy rheo-optical apparatus. The vesicles have been observed in static and flow, with different microscopy techniques, and the 3D shape has been reconstructed by image analysis. The main results is that surfactant multilamellar vesicles are deformed and oriented by the action of shear flow while keeping constant volume, and exhibit complex dynamic modes (i.e., tumbling, breathing and tank-treading). The vescicle deformation can be quantified as a function of the flow intensity, the results show some analogies with the case of the deformation of a single droplet immersed in an immiscible fluid, thus suggesting possible nondimensional scaling parameters.