Multiple droplets on a conical fiber: formation, motion, and droplet mergers

TL;DR

This study investigates how multiple droplets form, move, and merge on conical fibers, combining experiments and simulations to understand the influence of geometry and fluid properties on droplet dynamics.

Contribution

It provides new insights into droplet behavior on conical fibers, including formation, motion, and merging, with detailed experimental and numerical analysis.

Findings

Droplet size and spacing are controlled by Plateau-Rayleigh instability.

Droplets spontaneously move and merge due to size-dependent velocities.

Merging alters local droplet speed and affects film deposition.

Abstract

Small droplets on slender conical fibers spontaneously move along the fiber due to capillary action. The droplet motion depends on the geometry of the cone, the surface wettability, the surface tension, the viscosity, and the droplet size. Here we study with experiments and numerical simulations, the formation, spontaneous motion, and the eventual merger, of multiple droplets on slender conical fibers as they interact with each other. The droplet size and their spacing on the fibre is controlled by the Plateau-Rayleigh instability after dip-coating the conical fiber. Once these droplets are formed on the fiber, they spontaneously start to move. Since droplets of different size move with different speeds, they effectively coarsen the droplet patterning by merging on the fiber. The droplet merging process affects locally the droplet speed and alters the spatiotemporal film deposition on the fiber.