Using acoustic perturbations to tune bouncing on thickening cornstarch suspensions

You’ve undoubtedly encountered viral videos on social media showing people walking on pools of cornstarch suspensions without sinking. Such videos illustrate a fascinating property of suspensions: shear jamming under compression. Here, we investigate whether acoustic perturbations are a viable strategy for unjamming suspensions under compression. Specifically, we report on measurements of the coefficient of restitution for steel ball bearings bouncing a cornstarch suspension surface as a function of the impact energy and acoustic power for different weight fraction suspensions. We find that the coefficient of restitution depends sensitively on the weight fraction of cornstarch. In addition, we find that the coefficient of restitution, while constant for low impact energies, decreases at high impact energies as 1/impact energy. This decrease suggests an upper limit to the suspension elasticity. Finally, we demonstrate that acoustic perturbations can indeed change the coefficient of restitution, indicating this is a viable strategy for unjamming and, perhaps, making people sink on command as they walk across a pool filled with cornstarch suspension.