Dense suspensions: force response and jamming

The response of dense suspensions to an external force was studied using two different experiments. In the first experiment, objects were settled in a deep bath of a dense cornstarch suspension. This is the only suspension to result in two unexpected phenomena: Velocity oscillations in the bulk, and stop-go-cycles near the bottom. Both are believed to be caused by a change in the particle configuration within the suspension. In the second experiment, vertical vibrations were exerted to a thin layer of dense suspensions. Depending on suspension and shaking parameters, a lot of different unexpected phenomena were found: Stable and growing holes and fingerlike protrusions, to name a few. All have in common that hydrostatic pressure is overcome, which would normally cause a hole to collapse in any Newtonian liquid, even when vibrated. A convection roll was found on the edge of the holes in the suspensions, which might be explained by a break in symmetry in the oscillations of the hole edge, which in turn can cause a change in particle configuration in the suspension. A cornstarch suspension was found to be a remarkable one. Cornstarch was found to be the only suspension to show non-monotonic settling, and shows the richest phenomenology when shaken. The unique particle properties of the cornstarch, edgy particles with a relatively flat size distribution in the range of 5-20 micrometer, might be the cause of this behavior. No other, easily available, particles were found to have these properties.