Figure 6-13

Liquid between rails with actuated neck.

Ordinarily, the contact angle on both rails is 60 degrees. The neck is narrow enough to prevent progress then. But when the neck is electrically activated (electrowetting), the contact angle on the yellow part decreases to 30 degrees (and the color turns magenta), and the liquid can get through. It is important to note that the electrowetted area extends significantly past the neck, since the liquid has to get into the wide part of the channel before a 60 degree contact angle is sufficient for advance.