Vorticity banding during the lamellar-to-onion transition in a lyotropic surfactant solution in shear flow |
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Authors: | G M H Wilkins P D Olmsted |
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Institution: | (1) School of Physics and Astronomy, University of Leeds, LS2 9JT Leeds, UK |
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Abstract: | 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. |
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Keywords: | 47 57 Qk Complex fluids and colloidal systems: Rheological aspects 83 60 Wc Flow instabilities 83 80 Qr Surfactant and micellar systems associated polymers |
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