Using orthogonal shear and acoustic excitation to tune thickening and jamming in suspensions*

Running fast enough over a tub of thickening cornstarch suspension and not sinking is one of the most entertaining science demonstrations garnering millions of viewers every year. As stress is applied to the suspension, the cornstarch particles come close enough to form force chains that are capable of supporting the weight of a person. This thickening, while fun for demonstrations, causes problems for efficient processing of industrial suspensions and garners a high cost. Previously we showed that by applying fast orthogonal perturbations, the viscosity of suspensions under shear can be tuned and decreased by over an order of magnitude. Here, we show that impact driven jamming can be eliminated using a similar technique. Specifically, we conducted a series of impact and extensional flow experiments while cyclically oscillating the bottom plate of our rheometer about the vertical axis. We observe a drastic reduction in the normal forces when the oscillations are turned on. These experiments have the potential to alter suspension processing methods used in numerous industries.