Drop transport between two non-parallel plates via AC electrowetting-driven oscillation

We propose a simple transport method of drops inside a pair of non-parallel electrode plates with a small wedge angle by using AC electrowetting. We observe different drop transport behaviors depending on the frequency. At low frequency (10 Hz), a drop bounded by the plates moves quickly toward the narrower gap by the repeated wetting and de-wetting process. At high frequency (10 kHz), however, drops initially move slowly in the same direction with a small-amplitude of oscillation and then quickly penetrate the space at the narrower gap. Even if the drop does not touch the top plate, an electrostatic force can deform the drop to make a bridge, resulting in a similar drop motion. We also demonstrate the similar transport behavior of drops between a pair of parylene-coated plates with a smaller contact angle and a higher contact angle hysteresis than the Teflon and parylene-coated surface. We assert that the proposed method can control the transport of drops by using a simple geometric configuration and a simple electrical signal control.