Séminaire exceptionnel: Jeffrey F. Morris (CUNY)

The phenomenon of discontinuous shear thickening (DST) in concentrated suspensions has been rationalized as being due to the formation of frictional contacts formed when the imposed stress is sufficient to drive particles together.  This implies a balancing resisting force, whose magnitude sets the threshold for the imposed stress to induce contacts.  Thus, the number of contacts is an increasing function of stress, but it also fluctuates as the suspension flows. The resulting system can be thought of as a three-component system, composed of particles, fluid, and contacts.
 
The rheological behavior of highly concentrated suspensions, including DST and jamming, and the basis in the formation of contacts (and networks of these contacts) will be discussed in terms of simulation results that include hydrodynamic and frictional interactions, along with a repulsive force of short range.  This simulational model has been shown to reproduce the basic phenomenology seen in experiments on suspensions of near hard spheres. The work presented will focus on describing the development of rigid structures within the suspension, and relating their formation to the loss of degrees of freedom in their motion induced by frictional contacts.