Driven large contact angle droplets on chemically heterogeneous substrates

We study the depinning and subsequent motion of two-dimensional droplets with large contact angles that are driven by a body force on flat substrates decorated with a sinusoidal wettability pattern. To this end, we solve the Stokes equation employing a boundary element method. At the substrate a Navier slip condition and a spatially varying microscopic contact angle are imposed. Depending on the substrate properties, we observe a range of driving forces where resting and periodically moving droplets are found, even though inertial effects are neglected. This is possible in the considered overdamped regime because additional energy is stored in the non-equilibrium configuration of the droplet interfaces. Finally, we present the dependence of the driving at de- and repinning on wettability contrast and slip length, complemented by a bifurcation analysis of pinned-droplet configurations. Copyright (c) EPLA, 2012