Transport dynamics in open microfluidic grooves.

In microscopic rectangular grooves various liquid wetting morphologies can be found, depending on the wettability and details of the geometry. When these morphologies are combined with a method to vary the apparent contact angle reversibly, transitions between droplike objects and elongated liquid filaments can be induced. Liquid can thus be transported on demand along the grooves. The dynamics of liquid filaments advancing into grooves as well as receding from grooves has been studied, varying the contact angle using the electrowetting effect. The dynamics of the receding filament is purely capillarity driven and depends only on the contact angle, the viscosity of the liquid, and the geometry of the groove. The length and the dynamics of the advancing filaments, on the other hand, are strongly dependent on the ionic content of the liquid and the applied ac voltage.