  Electrowetting has a potential to realize stand-alone point-of-care (POC)
devices. Here we report droplet-migration characteristics on oil-infused
electrowetting-on-dielectric (EWOD) substrates. We prepare sparse micropillars
to retain the oil layer in order to exploit the layer as a lubricating film. A
physical model of the droplet velocity is developed, and effects of the
lubrication, the oil viscosity, the droplet volume, and the thickness of solid
and liquid dielectric layers are discussed. It is found that the droplet
velocity is scaled as square of E, which differs from a relationship of cube of
E for droplets sliding down on liquid-infused surfaces by gravity. Furthermore,
our device achieves droplet velocity of 1 mm/s at the applied voltage of 15 V.
The velocity is approximately tenfold as high as the same condition (applied
voltage and oil viscosity) on porous-structure-based liquid-infused surfaces.
The achieved high velocity is explained by a lubrication-flow effect.

Fluid Dynamics