Microfluidic SANS study of the lamellar-to-MLV transition in model surfactant system of varying membrane bending rigidity

The formation of multilamellar vesicles (MLVs) under flow can be achieved by tuning the shear field and by manipulating the lamellar membrane physical properties. Here we investigate the flow response of a model surfactant system, Sodium Dodecyl Sulfate (SDS)/octanol/brine, in the lamellar phase and, specifically, the mechanism and conditions required for the formation of MLVs. We employ microfluidics in continuous and oscillatory flow modes, to precisely control the shear magnitude, residence time, amplitude, and frequency. Small Angle Neutron Scattering (SANS) with a small beam footprint (illuminating down to 20 nL sample) was utilised to spatially and temporally resolve the lamellar to MLV transformation, in terms the structure factor and anisotropy of the scattering signal. Polarised optical microscopy provide complementary insight into the evolution of long range order accompanying the MLV transformation. In order to examine the effect of membrane bending rigidity on the conditions required for MLV formation, we have varied the membrane bending modulus by salt (NaCl) addition, and quantified its consequence to vesicle formation kinetics.