08/09/2017 – J. Comtet – Pairwise frictional profile between particles determines discontinuous shear thickening transition in non-colloidal suspensions
Séminaire régulier IUSTI – 8 sept. 2017 – 11h salle 250
Pairwise frictional profile between particles determines discontinuous shear thickening transition in non-colloidal suspensions
Jean Comtet – LPS ENS, Paris
The process by which sheared suspensions go through a dramatic change in viscosity is known as discontinuous shear thickening. Although well-characterized on the macroscale, the microscopic mechanisms at play in this transition are still poorly understood. Here, by developing new experimental procedures based on quartz-tuning fork atomic force microscopy, we measure the pairwise frictional profile between approaching pairs of polyvinylchloride and cornstarch particles in solvent. We report a clear transition from a low-friction regime, where pairs of particles support a finite normal load, while interacting purely hydrodynamically, to a high-friction regime characterized by hard repulsive contact between the particles and sliding friction. Critically, we show that the normal stress needed to enter the frictional regime at nanoscale matches the critical stress at which shear thickening occurs for macroscopic suspensions. Our experiments bridge nano and macroscales and provide long needed demonstration of the role of frictional forces in discontinuous shear thickening. Comtet, J., Chatté, G., Niguès, A., Bocquet, L., Siria, A., & Colin, A. Nature Communications, 8, 15633 (2017).