Shear Induced Structures in Lamellar Systems

Abstract

Shear flow induces the formation of multilamellar vesicles (MLV, also termed "onions") in the lamellar phase of the nonionic surfactant C 10 E 3 in water. Depending on the applied shear rate, one can reach a state of polydisperse MLV (at intermediate shear rates) or densely packed monodisperse MLV at high shear rates. In this contribution we investigated the structure evolution when the shear rate is reduced by means of rheo-microscopy as well as rheo-small angle light and neutron scattering (SALS, SANS). Different shear quenches within the MLV structure region of 40 wt% C 10 E 3 reveal two different MLV size growth mechanisms: (i) a continuous and (ii) a discontinuous MLV size growth. In the later case, a part of the initial MLV structure transforms into planar lamellar domains leading to shear thinning. The lamellar domains perform a re-orientation process from parallel oriented lamellae into MLV in coexistence with the initial MLV structure. The pathway of the transformation of the parallel lamellae to MLV is the same as in start-up experiments, i.e. from a homeotropically aligned lamellar phase.