How to make sticky surfaces slippery: Contact angle hysteresis in electrowetting with alternating voltage

Contact angle hysteresis caused by random pinning forces is a major obstacle in moving small quantities of liquid on solid surfaces. Here, we demonstrate that the contact angle hysteresis for sessile drops in electrowetting almost disappears with increasing alternating voltage, whereas for direct voltage it remains constant. This observation is explained in terms of a balance of surface tension, pinning, and (time-dependent) electrostatic forces at the contact line.