Texture-driven elastohydrodynamic bouncing

We investigate in detail the dynamics of bouncing of a fluid-immersed solid sphere onto a textured wall at moderate Reynolds and Stokes numbers. Using high-frequency interferometric measurements, the dynamics of the sphere is resolved in time and space, before, during and after collision with the wall. The critical Stokes number for bouncing is shown to be significantly influenced by the geometry of the texture, i.e. the surface fraction and the height of the micro-pillars. A modified Hertz model is developed to take into account the influence of this texture geometry on the collision dynamics. The predicted scaling for the collision time and penetration depth of the sphere into the textured wall is found to be in good agreement with the experimental measurements.