Retraction dynamics of an impacting droplet on a rotating surface

In this study, we experimentally measure and characterize the behavior of water droplet impact on the center of superhydrophobic surface, focusing on the dynamics in the retraction stage. The circumferential velocity in the retracting liquid film rapidly amplifies, generating a centrifugal force which either induces rapid rebound by changing the shape of the bouncing droplet into a spinning-top or inhibits the rebound of the droplet. We measure the flow field in the retracting liquid film and reveal the coupling between the increasing circumferential velocity and droplet's decreasing radius in the retraction stage. We adopt a simplified approach to calculate the retraction velocity and the development of the circumferential velocity in the retracting liquid film. Finally, we reveal that the rebound of the droplet is weakened by the centrifugal force with a transition to nonbouncing around a critical Froude number (Fr≈2.4). Good agreements are found between the theoretically predicted parameters and the experimentally measured ones.