Directed droplet motion along thin fibers.

When microscopic droplets are placed between fibers held at a fixed angle, the droplets spontaneously move toward the apex of the fibers. The speed of the droplet motion increases both with the angle between the fibers and the distance the droplet spans across the fibers. The speed of these droplets can be described by a simple scaling relationship. Bending these fibers into a sawtooth geometry results in a droplet ratchet where cyclic motion in a fiber results in extended linear motion of the droplet, and can even be used to induce droplet mergers.