Frequency-dependent contact angle hysteresis in electrowetting

Abstract

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 programming of droplet stickiness or sliding.

Electrically Mediated Static Contact Angle and Hysteresis of Polyelectrolyte Solutions

“…Thus, fully ionized PAA solutions exhibited an ∼50% increase in electrowetting hysteresis over weakly ionized PAA solutions. In a number of studies, it has been found that the electrowetting hysteresis is primarily caused by the roughness of the substrate surface and chemical heterogeneity. − Notably, the dielectric surfaces in our experiments for PAA at low and high pHs had identical chemical properties and physical roughness. Therefore, it is reasonable to conclude that the PE ionization level affects the electrowetting hysteresis.…”