Shear-induced fragmentation of Laponite suspensions
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Simultaneous rheological and velocity profile measurements are performed in a smooth Couette geometry on Laponite suspensions seeded with glass microspheres and undergoing the shear-induced solid-to-fluid (or yielding) transition. Under these slippery boundary conditions, a rich temporal behaviour is uncovered, in which shear localization is observed at short times, that rapidly gives way to a highly heterogeneous flow characterized by intermittent switching from plug-like flow to linear velocity profiles. Such a temporal behaviour is linked to the fragmentation of the initially solid sample into blocks separated by fluidized regions. These solid pieces get progressively eroded over time scales ranging from a few minutes to several hours depending on the applied shear rate $\dotγ$. The steady-state is characterized by a homogeneous flow with almost negligible wall slip. The characteristic time scale for erosion is shown to diverge below some critical shear rate $\dotγ^\star$ and to scale as $(\dotγ-\dotγ^\star)^{-n}$ with $n\simeq 2$ above $\dotγ^\star$. A tentative model for erosion is discussed together with open questions raised by the present results.
19 pages, 13 figures, submitted to Soft Matter
19 pages, 13 figures, submitted to Soft Matter