Vendredi 22 novembre 2024 à 11h00 ; salle 357 / IUSTI
Particle-liquid suspensions behave like Newtonian fluids at low particle concentration, but exhibit shear thickening, or rise in the viscosity with shear rate, at moderate-to-high concentration. The prevailing consensus is that shear thickening results from particle interactions transitioning from lubricated to frictional contact. However, many studies report Newtonian rheology beyond the discontinuous thickening transition, which is inconsistent with stress transmission through frictional contacts. Moreover, experimental studies pre-shear the suspension for long durations before observing shear thickening, without providing a rationale for lengthy pre-shear. We present experimental evidence that shows the rheology is determined by a hitherto unrecognized factor, the shear strain. At low shear stress, the rheology is Newtonian regardless of shear strain; above a critical shear stress, the rheology evolves with strain, transitioning from continuous shear thickening, to discontinuous shear thickening, followed by a pronounced non-monotonic `S-shaped’ response, and finally to a shear thinning state that resembles a dry granular medium. We argue that large shear strain is required for cooperative alignment of particles clusters that lead to formation of a system-spanning contact network.