title: Velocity oscillations and stop-go cycles: the trajectory of an object settling in a cornstarch suspension.
abstract: We present results for objects settling in a cornstarch suspension. Two surprising phenomena can be found in concentrated suspensions. First, the settling object does not attain a terminal velocity but exhibits oscillations around a terminal velocity when traveling through the bulk of the liquid. Second, close to the bottom, the object comes to a full stop but then reaccelerates before coming to another stop. This cycle can be repeated up to 6 or 7 times before the object reaches the bottom to come to a final stop. For the bulk, we show that shear-thickening models are insufficient to account for the observed oscillations and that the history of the suspension needs to be taken into account. A hysteretic model, that goes beyond the traditional viscoelastic ones, describes the experiments quite well but still misses some details. The behavior at the bottom can be modeled with a minimal jamming model.
authors.affiliation: Physics of Fluids Group, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Stefan
authors.initials: S
authors.lastname: von Kann
authors.forename: Jacco H
authors.initials: JH
authors.lastname: Snoeijer
authors.forename: Devaraj
authors.initials: D
authors.lastname: van der Meer