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Rheology of non-Brownian concentrated suspensions : the role of contact forces between particles
Creeping flows of non-Brownian suspensions are ubiquitous in industrial processes (charged polymers, fresh concrete, solid rocket propellants…) as well as in natural phenomena (sedimentary flows, landslides…). Even when the suspending fluid is Newtonian, these concentrated suspensions exhibit a complex rheology. For instance, when they are sheared, concentrated suspensions can behave as shear-thinning or shear-thickening fluids, anisotropic normal stresses arise, particle trajectory irreversibility is observed, even for small Reynolds number flows…
Since Einstein’s work in 1906 on the viscosity of diluted suspensions, numerous experimental, theoretical and numerical studies have been devoted to the understanding of these complex phenomena. The theoretical descriptions have long focused on hydrodynamic interactions which are quite complicated as they involve very different scales, long-range interaction on one hand and lubricated contacts on the other hand. However, models based on hydrodynamic interactions alone failed to capture the complex rheological behavior of concentrated suspensions and the question of the role of direct forces coupled to the shear-induced microstructure on suspension rheology became more and more important and is now central.
In this talk, I will discuss some recent aspects of the physics of non-Brownian suspension flows that emphasize the complexity of their behavior. And, after this short review, I will show how direct microstructural measurements allow evidencing the presence of solid contacts between particles. Then, I will present both numerical and experimental results on the role played by these contacts on suspension rheology.