片栗粉懸濁液の上を走るための粘弾性特性

（衝突実験による粘弾性計測）

抄録

Dense suspension of non-Brownian particles such as potato starch often shows counter-intuitive behaviors due to its discontinuous rheological property. Using this particular rheological property, people can run on a dense suspension. However, once the motion of leg becomes too slow, the leg is arrested, namely, it is difficult to walk on the surface. To explain this peculiar behavior, propagation of jamming front caused by an impact onto a dense suspension has been considered recently. The effectively solidified zone is developed by the jamming-front propagation. This solidified zone effectively increases viscosity of the suspension. In addition, when the jamming front reaches the bottom of the container, a solidified pillar which causes effective elasticity is developed. Because the lifetime of the solidified zone is short, the suspension recovers usual viscosity after a while. To characterize the viscoelastic properties of the impacted dense suspension, a set of simple impact experiments was performed. A solid sphere was dropped from a certain height onto a suspension. The impact and rebound dynamics were recorded by a high-speed camera. Using the kinematic data, viscoelasticity of the impacted suspension was measured. The obtained data are consistent with the idea of jamming-front propagation. In addition to the impact onto a static target, impact experiments onto a dense suspension under the influence of mechanical vibration were also performed. Although the mechanical vibration can significantly deform the free surface of suspension, the impact response was hardly affected. In this article, a brief review of the impact-induced jamming-front propagation and the resultant effective viscoelasticity is presented.