Unidirectional droplet motion on crosswise-striped surface

The behaviour of a droplet settled on an energetically heterogeneous surface is studied by simulation and simplified analytical methods. The surface energy inhomogeneities are represented by a pattern of a series of parallel stripes of monotonically increasing width and two different contact angles. The isotropic random forces acting on the droplet induce a highly asymmetric movement of the droplet. The observed shift of the droplet is perpendicular to the stripes and directed towards decreasing width of the stripes. The system behavior described as a series of droplet positions and morphologies in local stationary states is studied by means of simulations with a finite-element method performed by the Surface Evolver program. The influence of chosen system parameters on the droplet trajectory is considered, including the details of the surface pattern, the fluctuation temperature, the surface and line tensions. The influence of model parameters on the trajectory of the droplet is discussed. A simple analytical model explaining the droplet translocation is proposed.