Bridging the gap between colloidal and granular rheology

In suspension rheology, size matters. Many concentrated industrial dispersions, e.g. chocolate and ceramics, feature complex particle size distributions spanning several orders of magnitude in diameter. The particles, which may have complicated shapes and interactions, can range in size from <100 nm to >100 micron. At the high volume fractions involved subtle changes to the size distribution can have profound implications for the flow behaviour. It is therefore surprising that even for the simplest case of monodisperse repulsive spheres the effect of particle size on rheology is poorly understood. Most prior work focuses on two regimes at opposite ends of the size spectrum: colloidal (diameter<1 micron) and granular (>>10 micron) particles. There are fundamental differences between these regimes and it is not clear how to relate the two, or what happens for particles of intermediate size.

Here I present our work on bridging the gap between colloidal and granular rheology. The transition between the two is related to a well-known (but not entirely understood) phenomenon: shear thickening. This represents an important first step toward understanding the multimodal dispersions common in industry.