Mechanical aging and non-linear rheology of concentrated colloidal suspensions: experimental facts and simple models

Many colloidal systems display very non-Newtonian and solid-like behaviour when concentrated, a striking feature being the apparition of a yield stress. After recalling some basics about the interactions between colloidal particles, I present a few experimental facts commonly observed in these systems: aging and non-linear rheology. A simple phenomenological model is then introduced, in which the local state of the system is described by a single scalar parameter, the fluidity. I proceed with comments on heterogeneous flows in some of these systems. These notes are not intended to be a comprehensive review, and the reader is directed to the references for further reading