Electrowetting control of an oscillating contact line

  The control of contact line (CL) conditions holds significant importance in various practical flow scenarios, such as painting and coating processes. Notably, the boundary condition of an oscillating CL proves to be more intricate compared to a steadily moving CL in a single direction. Our previous work has demonstrated that this complexity arises from the presence of a phase delay in the former case, introducing a temporal misalignment between the velocity of the contact line and the dynamic contact angle.

  In this study, we examine the effects of electrowetting on the behavior of an oscillating CL. When an alternating electrical field is applied to a mechanically vibrating drop, the moving CL exhibits stick-slip behavior. This behavior mimics movement over a microstructured rough surface, despite the fact that it actually moves over a flat surface. The AC electrical field creates an emulated microstructural effect, serving as the opposite counterpart to the cloaking effect of a DC electrical field, which deactivates the hindrance to spreading caused by microstructure during spontaneous wetting.

  Moreover, the frequency dependence of the dielectric response results in varying impacts of different AC frequencies on CL motion. We found that higher AC frequencies more strongly impede CL movement. Additionally, when the frequency of the electrical force matches the frequency of the mechanical vibration, the drop oscillation is enhanced.