From dry quicksand to unsinkable suspensions: Exploring the underlying links between dry granular flow and wet suspensions

The flow behaviour of dry granular materials, e.g. free flowing sand, is commonly observed to be very different from wet suspensions, e.g. sticky cornstarch-water mixtures. We show, through particle simulations and rheology experiments, that the different behaviour can be put in a unifying rheological framework, where the interplay between particle-size scaling and the observation window gives rise to the perception. More interestingly, the underlying microstructure and force networks bear surprising similarities, which can be used to understand many sometimes puzzling non-linear flow phenomena.

A particular example is shear thickening, where suspension viscosity increases with shear stress or shear rate. It is a ubiquitous feature of many different particle systems and flow processes in nature and industry, particularly for particles of intermediate sizes (diameter 1 μm ≤  d ≤ 50 μm) at high concentrations. This phenomenon has been traditionally explained as being driven purely by hydrodynamic interactions. However, recent theoretical, modelling and experimental work has shown the inadequacy of this mechanism, by elucidating the important role of frictional particle contact.

In this talk, I will present experimental and simulation evidence for shear thickening as a transition from a typical colloidal to a granular behaviour, in which the formation of frictional non-hydrodynamic contacts is key. We have directly quantified the contact contribution to the suspension viscosity during shear thickening by means of shear-reversal rheological measurements, providing new and unambiguous evidence. I will finally describe the ‘tuning’ of shear thickening and other rheological properties based on the understanding of particle contacts, by means of active control or suspension formulation.

Visualization of the simulation of a homogeneously sheared dense suspension. Red: particle contacts; blue: lubrication interactions


Dr Jin Sun is a Reader in the School of Engineering at the University of Edinburgh. He graduated from Iowa State University in 2007 with a PhD in Mechanical and Chemical Engineering and did postdoctoral research in Chemical Engineering at Princeton University until 2010. His main research interests are in rheology and flow of dense particle systems in industrial and natural environments, such as manufacturing of ceramics, food stuff, battery electrodes and pharmaceuticals and debris and pyroclastic flows. He has been principal investigator of three UK EPSRC projects (total value ~£2.4M), currently leading the “Predictive formulation of high-solid-content complex dispersions” project; and co-investigator on three EU projects (~€11M), working on particle-fluid simulation method development.  He has been awarded a Royal Academy of Engineering/ Leverhulme Trust Senior Research Fellowship to explore the novel application of suspension rheology in 4D printing technology.