Vendredi 25 Mars 2016 à 10h : Séminaire FERMaT de Jeff Morris : « Simulation of frictional interactions in viscous suspensions : discontinuous shear thickening and shear jamming »
This talk addresses abrupt or “discontinuous” shear thickening (DST), in which the viscosity may suddenly change by orders of magnitude as shear rate is increased in suspension at large solid fraction. For many years, DST has been known, and popular videos of running on “oobleck” (cornstarch suspended in water) are found on-line. Corn starch is essentially non-Brownian, as the particles are above 10 microns in linear dimension, while the majority of experiments on this topic are for Brownian colloidal dispersions. Here we study the fundamental basis for DST, which has been mysterious and controversial.
A simulation method based on a quite minimal model—including viscous, electrostatic repulsion and contact frictional interactions between particles—has been shown to reproduce DST for both Brownian and non-Brownian suspensions as the rate is increased. The essential idea is that at low shear rate (or low shear stress) repulsive forces maintain particles at sufficient separation that their relative motion is “lubricated” by a thin liquid film, while under large stress the particles make frictional contacts.
The mechanism leading to the large change in properties is thus found in the development of a contact network between the particles ; this network changes dramatically as the critical shear rate is surpassed. Brownian motion serves as a repulsive force between particles in a suspension under shear, and we find that the influences of Brownian and stabilizing colloidal forces (for example, due to electrostatic repulsion or grafted polymer layers) are additive in delaying the transition from a lubricated (low-viscosity) to a frictional (high-viscosity) state.
- Thème du séminaire : Simulation of frictional interactions in viscous suspensions : discontinuous shear thickening and shear jamming
- Conférencier : Jeffrey F. Morris Levich Institute and Department of Chemical Engineering - The City College of New York
- Quand : Vendredidi 25 mars 2016 à 10h
- Où ? : Amphi 100, Campus INP-ENSIACET
- Séminaire ouvert à tous sans inscription
- Contact : Yannick Hallez