Flow of wormlike
micelles: from shear banding to elastic turbulence
Sandra Lerouge
Université Paris-Diderot, France
Abstract
Shear banding is an ubiquitous phenomenon in complex fluids flows. Most often
it corresponds to a flow state in which a fluid splits into layers of differing
apparent viscosities supporting different local shear rates. Shear banding has
been observed, either transiently or at steady state, in different classes of
complex systems including polymeric fluids and soft glassy materials. Its
description and understanding is particularly advanced in surfactant wormlike
micelles, for which the experimental evidence of its mechanical signature dates
back to the 1990s. Over the past 10 years a strong effort was made to combine
global rheology with local time-resolved techniques to probe both the velocity
field and the structural properties in various macro- and micro-fluidic
geometries. Overall, complex flows have been observed to emerge on top of the
shear-banding flow and have been connected to the development of viscoelastic
instabilities.
In this talk I will try to describe the complete picture of the shear-banding
transition in wormlike micelles flowing in Taylor-Couette geometry, from the
onset of banding to the development of elastic turbulence. The response of
shear-banding wormlike to time-dependent flow protocols such as step stress and
shear startup will be examined. The mechanical signatures
of the onset of banding will be discussed and compared with general criteria
derived by Moorcroft and Fielding. Then I will describe the spatio-temporal
dynamics over longer time scales showing the development of secondary flows on
top of shear banding. I will also address the transition towards a disordered
flow state reminiscent of elastic turbulence in regular polymers. Finally, we
will see that non-shear banding wormlike micelles also exhibit elastic
instabilities and turbulence, providing a way to explore a large range of
elasticity numbers.
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