Alladi Ramakrishnan Hall

Yielding and flow of confined jammed materials

Pinaki Chaudhuri

Institute for Theoretical Physics II (Soft Matter), University of Dusseldorf, Germany

A defining mechanical property of amorphous materials is the existence of a yield stress - the material only yields when the applied stress exceeds a threshold value.  Understanding the mechanisms of yielding and subsequent flow, in soft jammed systems, is important for a variety of rheological applications. In recent times, it has been proposed that spatially correlated events drive the flow of such materials, implying that spatial confinement would impact the nature of dynamical properties.

Using numerical simulations of model yield-stress fluids (colloids, emulsions etc), we investigate the response behaviour of confined materials around the flow threshold. We show that, for Couette flow, one observes a pronounced creeping regime near the yield stress, which is associated with strong spatio-temporal heterogeneity in dynamics. For the Poiseuille flow, we observe that the limiting value of the wall-stress at which steady flow is observed, shifts to larger  magnitudes, compared to the case of the Couette flow.  Further, we discuss how such dynamical heterogeneities crop up during steady flow and connect that to observations of shearbanding in different soft glassy systems.