Droplet Helical Motion on Twisted Fibers.

We investigate herein the impact of helical structures on the motion of asymmetrical droplets along vertically twisted fibers. The droplet adopts helical motion around the bundle driven by gravity. This complex motion can be manipulated by varying the twists turns of the fibers. When the droplet size is smaller than the characteristic length of the helix (pitch), the droplet adopts a predominant helical motion correlated to the groove of the twisted fibers. When the droplet size exceeds the pitch length, a mixed motion of intermittent vertical sliding and helical movement emerges. A model describes rotational and linear speeds as a function of the number of fiber twist turns. This research highlights the profound role of substructures in droplet dynamics, offering fresh insight into droplet manipulation or fiber-based devices.