Capillary transport from barrel to clamshell droplets on conical fibers

Abstract

Droplets spontaneously move when they are placed at the tip of a cone surface. Using three dimensionally printed structures, we experimentally explore a large panel of configurations regarding the aperture angle of the cone. We evidence a change of the droplet geometry while moving along the conical fiber. This transition is a switch of configuration from barrel to clamshell shape. The consequence is a change in the droplet dynamics. We estimate the position of this geometrical transition and we propose two models to describe the motion of the barrel and the clamshell droplets. While both shapes are driven by capillary forces, the dissipation is dependent on the geometrical configuration. For barrel shape droplets the main dissipation appears to be in the liquid wedge. For clamshell shape droplets the dissipation occurs mainly in the liquid film close to the conical fiber.