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When a water droplet strikes a superhydrophobic surface, there may be several to a few tens of rebounds before it comes to rest. Although this intriguing multiphase flow phenomenon has received a great deal of attention from interfacial scientists and engineers, the underlying dynamics have not yet been completely resolved. In this paper, we report on an experimental investigation into the bouncing behavior of water droplets impinging on macroscopically flat superhydrophobic surfaces. We show that the restitution coefficient, which quantifies the energy consumed during impact and rebound, exhibits a nonmonotonic dependence on the Weber number. It is the droplet–surface friction that restricts the rebound height of the impinging droplet, so its restitution coefficient increases with the Weber number when the impact velocity is below a critical value. Above this value, the viscous friction within a thin liquid layer close to the superhydrophobic surface becomes dominant, and thus, the restitution coefficient decreases sharply. On the basis of energy analyses, semiempirical formulas are proposed to describe the restitution coefficient, and these can be employed to predict the number of successive rebounds of impinging droplets on superhydrophobic surfaces.

Droplet manipulation on solid surfaces is a key technique involved in a variety of applications ranging from self‐cleaning coatings to micro total analysis systems, and thus has been extensively investigated over the recent years. Here, an attempt is made to provide an overview of the latest developed strategies for controlling droplet dynamics, which include droplet motion mediated by surface wettability gradient or external actuation sources, and liquid transport at high‐temperature surfaces or high‐energy surfaces. More specifically, the working mechanism of diverse strategies is introduced, and their advantages and disadvantages are compared, based on which, an outlook of the future development of their applications is provided.

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