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Shear thickening in dense suspensions: revealing the frictional transition

Abstract : Shear thickening is a spectacular phenomenon which takes place in some dense suspensions. It manifests itself by a brutal increase of the suspension's viscosity above a certain critical stress. The most iconic example of shear-thickening suspensions is cornstarch and water mixes. Shear thickening long remained a mystery, until recent theoretical and numerical works which proposed a consistent microscopic model. This model explains the shear thickening transition as a frictional one due to the presence of a repulsive force between the grains.During my PhD, I provided one of the first direct experimental proofs of this mechanism. Inspired by granular physics, I showed that shear-thickening suspensions possess a frictionless flowing state at low granular pressure, which is consistent with the proposed model. I then evidenced the frictional transition with controlled experiments using suspensions of silica beads in ionic solutions. To do this, I developed new rheological techniques enabling pressure imposed measurements. Indeed, standard rheological tools do not allow access to the frictional properties of suspensions. The only rheometer that does that is not adapted to the suspensions we study here, which are colloidal. This work thus paves the way for the development of a new generation of pressure imposed rheometers, giving access to colloidal suspensions friction, which is a major challenge in complex fluids rheology.
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Cécile Clavaud. Shear thickening in dense suspensions: revealing the frictional transition. Soft Condensed Matter [cond-mat.soft]. Aix Marseille Université, 2018. English. ⟨tel-01970535⟩

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