Shear thicknening suspensions: from innovative rheological tools to hydrodynamics – ScienceFriction
Shear thickening occurs in dense particulate suspensions whose viscosity increase dramatically, sometimes by several orders of magnitude, when the imposed shear rate exceeds a critical value. Considered as an ubiquitous phenomenon in suspended materials, this behavior can be highly problematic for instance damaging pumps and mixers, or clogging pipes in industrial processes. It can also be very useful to technological applications such as liquid armors, smart dampers or modern concretes. For long considered as a puzzle, shear thickening has received a coherent framework within the frictional transition model which is supported both by discrete numerical simulations and experiments. These results indicate that shear thickening is driven by the activation of friction between particles above an onset stress needed to overcome repulsive forces between them. At low shear stress, particles immersed in the suspending fluid, behave as if frictionless since a short range repulsive force prevents them from making contact: the suspension flows easily. Conversely, above a critical stress, the suspension suddenly turns into a solid because particles are pressed into frictional contacts which are highly dissipative.
With this new paradigm, it is, for the first time, possible to consider establishing constitutive laws and build an hydrodynamics for shear thickening suspensions. These are the guidelines of the present ScienceFriction project. A major need to achieve this goal is to access to the friction coefficient of these suspensions, composed of micro-metric particles, where both contacts and colloidal interactions are simultaneously at play. This information is key to characterize them, however, it is inaccessible to conventional rheology. The ground of our project is the development of news experimental and numerical rheological tools enabling frictional measurements close to jamming thanks to pressure-imposed rheology (WP1). We will then use these tools to establish the constitutive laws of shear thickening suspensions in both steady and transients states (WP2). We will finally apply these constitutive laws beyond rheometry to tackle the flow of shear thickening suspensions in hydrodynamic configurations (flow down incline, pipe flow). These topics are largely unexplored, yet critical for industrial applications (WP3).
A distinctive feature of our project is that the above points will be addressed on model suspensions but also on industrial suspensions thanks to a collaboration with the French company CHRYSO (P3), a world leader for the development of polymers (superplastisizer) entering the composition of concrete. Altering the particle surface physical-chemistry has long been used by industrials to modify the flowing properties of suspensions but the approach remained mainly empirical. The recent understanding that the macroscopic behavior of shear-thickening suspensions is controled by the combined effect of friction and short range repulsive forces opens new perspectives. The advanced rheometers developed in this project will give the means to make the connection between friction coefficients and polymer technologies and dosages. It may therefore help design more efficient molecules, leading to better modern concrete formulations.
To achieve this program, 4 partners are involved: 2 French academic laboratories, IUSTI Marseille (expert in granular and suspension flow experiments) and LiPhy grenoble (expert in numerical simulations), 1 foreign laboratory EPFL Lausanne (expert in modeling suspension flows) and the company CHRYSO (expert in the formulation of superplastisizer for modern concretes). Our project also relies on 2 other external collaborations with academic laboratories : the LGC Toulouse (surface physico-chemistry), the InPhyNi Nice (characterizing friction at the particle scale).
Monsieur Bloen Metzger (Institut universitaire des systèmes thermiques industriels)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IUSTI Institut universitaire des systèmes thermiques industriels
EPFL / PCSL
LIPHY Laboratoire Interdisciplinaire de Physique
Help of the ANR 447,759 euros
Beginning and duration of the scientific project: January 2019 - 48 Months