Ratchetlike Motion of a Shaken Drop

We study the motion of a drop lying on a plate simultaneously submitted to horizontal and vertical harmonic vibrations. The two driving vibrations are adjusted to the same frequency, and, according to their relative amplitude and phase difference Delta Phi, the drop experiences a controlled directed motion with a tunable velocity. We present a simple model putting in evidence the underlying mechanism leading to this ratchetlike motion of the drop. Our model includes the particular case Delta Phi=pi corresponding to the climbing of a drop on a vertically vibrated inclined substrate, as recently observed by Brunet et al. [Phys. Rev. Lett. 99, 144501 (2007)]. This study gives insights in the fundamental issue of wetting dynamics and offers new possibilities of controlled motion in droplet microfluidics applications.