Droplet impact on rotating surfaces: The effect of centrifugal force and wettability on spreading dynamics

Droplet impact on rotating surfaces experiences the tangential shear force from the rotating surface, generating a centrifugal force that either enhances the spreading or destabilizes the expanding lamella. In this study, we experimentally characterize the impact of a water droplet on rotating surfaces with various wettabilities, and theoretically analyze the observed impacting dynamics, including the enhanced spreading and the transition to the destabilization of the expanding lamella. Liquids with a wide range of viscosity are tested to explore the effect of liquid viscosity on the impacting dynamics. We propose a simplified approach to predict the tangential velocity induced by the surface's tangential shear force, and validate the predicted velocity by flow field measurement. We further deduce a quantitative description for the maximum spreading factor in the spreading regime, and derive the critical condition for the destabilization of the lamella for a water droplet. Good agreements are found between the predicted values and the measured ones for the impact on the rotating surfaces with various wettabilities.