  The dynamic behavior of a partially wetting polymer droplet driven over a
nanostructured interface is studied using molecular dynamics simulations. We
consider the bead-spring model to represent a polymeric liquid that partially
wets a rough surface composed of a periodic array of spherical particles. It is
shown that at sufficiently small values of the external force, the droplet
remains pinned at the particles' surface, while above the threshold, its motion
consists of alternating periods of pinning and rapid displacements between
neighboring particles. The latter process involves large periodic variation of
the advancing and receding contact angles due to attachment and detachment of
the contact line. Finally, upon increasing external force, the droplet center
of mass is displaced steadily but the oscillation amplitude of the receding
contact angle as well as the maximum contact angle hysteresis remain relatively
unaffected.
