Dense suspensions are granular materials that are suspended in a liquid at high packing fractions. Familiar examples of dense suspensions are mud and mixtures of cornstarch with water (a.k.a. “Oobleck”). These materials are a subset of complex fluids, and often exhibit strong non-Newtonian behaviour such as discontinuous shear thickening.

Jamming is an important aspect of these dense suspensions because of their high packing fraction. A jammed packing behaves effectively like an amorphous solid, and we can consequently make dense suspensions switch between fluid and solid states by perturbing their boundary conditions.

Dynamic Jamming

Dense suspensions can be prepared arbitrary close to the jamming point. A strong perturbation through, for example, an impact, can result in local jamming and consequently the formation of a jamming front the propagates through the system. The image above shows such a jamming front in a quasi two-dimensional system. The propagation speed of these fronts is much faster than the impact speed and becomes faster as the initial state gets closer to the jamming point.

Publications:
[1] I.R. Peters, S. Majumdar, and H.M. Jaeger, Direct observation of dynamic shear jamming in dense suspensions. Nature 532, 214-217 (2016) [doi / full text]
[2] I.R. Peters and H.M. Jaeger, Quasi-2D dynamic jamming in cornstarch suspensions: visualization and force measurements. Soft Matter 10, 6564 (2014) [pdf]
[3] E. Han, I.R. Peters, and H.M. Jaeger, High-speed ultrasound imaging in dense suspensions reveals impact-activated solidification due to dynamic shear jamming. Nature Comm. 7, 12243 (2016) [doi]

Splashing of suspension droplets

Just like with ordinary fluids, you can make droplets out of dense suspensions. When looking at their splashing behaviour, however, there are some surprises. Unlike with ordinary fluid droplets, the splashing transition of these suspension droplets cannot be predicted by global properties of the fluid, but instead is fully described by an energy balance on the level of individual particles. Collisions between the particles in the suspension are of great importance to understand the behaviour of these droplets.

Publications:
[1] I.R. Peters, Q. Xu, and H.M. Jaeger, Splashing Onset in Dense Suspension Droplets. Phys. Rev. Lett. 111, 028301 (2013) [pdf]
[2] M.H. Klein Schaarsberg, I.R. Peters, M. Stern, K. Dodge, W.W. Zhang, and H.M. Jaeger, From splashing to bouncing: The influence of viscosity on the impact of suspension droplets on a solid surface. Phys. Rev. E 93, 062609 (2016) [pdf]
[3] Q. Xu, I.R. Peters, S. Wilken, E. Brown, and H.M. Jaeger, Fast Imaging Technique to study Drop Impact Dynamics of non-Newtonian Fluids, J. Vis. Exp. 85, 51249 (2014) [pdf]