Directed droplet motion induced by vibration of the solid support

The unidirectional motion of a droplet settled on an energetically heterogeneous surface undergoing mechanical vibration is studied by means of simulations with a finite element method performed by the Surface Evolver simulation program. The surface energy inhomogeneities are represented by a pattern of a series of parallel stripes of monotonically increasing width and two alternating contact angles. In certain circumstances, the observed shift of the droplet is perpendicular to the stripes and directed toward the increasing width of the stripes. The influence of model parameters on the trajectory of the droplet is discussed. A full profile of the droplet energy along the droplet trajectory was estimated on the basis of density distribution of positions occupied by the droplet along the travel coordinates. The influence of model parameters on the trajectory of the droplet is discussed. On the basis of the asymmetric properties of the energy profile, the ratchet mechanism of unidirectional droplet motion was postulated.