Vorticity banding during the lamellar-to-onion transition in a lyotropic surfactant solution in shear flow
School of Physics and Astronomy, University of Leeds, LS2 9JT, Leeds, UK
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Accepted: 31 October 2006
Published online: 1 December 2006
We report on the rheology of a lyotropic lamellar surfactant solution (SDS/dodecane/pentanol/ water), and identify a discontinuous transition between two shear thinning regimes which correspond to the low-stress lamellar phase and the more viscous shear-induced multilamellar vesicle, or “onion” phase. We study in detail the flow curve, stress as a function of shear rate, during the transition region, and present evidence that the region consists of a shear-banded phase where the material has macroscopically separated into bands of lamellae and onions stacked in the vorticity direction. We infer very slow and irregular transformations from lamellae to onions as the stress is increased through the two-phase region, and identify distinct events consistent with the nucleation of small fractions of onions that coexist with sheared lamellae.
PACS: 47.57.Qk Complex fluids and colloidal systems: Rheological aspects – / 83.60.Wc Flow instabilities – / 83.80.Qr Surfactant and micellar systems, associated polymers –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2006