Frequency-dependent contact angle hysteresis in electrowetting

Contact angle hysteresis determines the stickiness of liquid on surfaces. Yet, the adjustment of contact angle hysteresis remains highly challenging and extremely work-intensive. Here, we reveal a quadratic growth of contact angle hysteresis upon strengthening the inhomogeneous electric field in electrowetting under both direct and alternating current supplies. The anomalous evolution of contact angles under alternating current supplies is quantitatively interpreted by the oscillation of electrowetting forces and the observability of the contact line motion in experiments. This work provides a feasible, reversible, and versatile approach for on-demand programing of droplet stickiness or sliding.