Tap dance of a water droplet

Electro-elasto-capillarity (EEC) is a new method of droplet encapsulation controlled by an electric field. In this paper, we report some experiments, for the first time, to realize EEC under a dynamic electric field, showing the progress of electrowetting on a moving substrate. We employ the combined effects of surface tension, elastic force and Coulomb force to manipulate the flexible thin film to encapsulate and release a tiny droplet in a controllable and reversible manner. An alternating current electric field is applied to actuate the droplet and film to vibrate, as if they are dancing to a melody. We measured the frequency of the droplet and the film vibration and found that it was twice the input signal; we also carried out frequency analysis experiments. The frequency-doubling phenomenon can be explained theoretically. Our findings may offer a practical method for drug encapsulation and for the actuation of microelectromechanical system devices.